PART 2
REPORTS OF SECTIONS

SECTION 1
ENVIRONMENTAL CONSIDERATIONS AND SITE SELECTION IN COASTAL AQUACULTURE

Contributed Papers (CPs)¹ - 3, 6, 7, 10, 12, 14, 21, 22, 23, 24
Background Papers (BPs)² - 2, 3, 4, 5, 7, 8, 11, 12, 13, 14, 15, 18, 19, 20

1. OVERVIEW - P. Menasveta (Chairman on Environmental Considerations)

Aquaculture has a high potential for future development. This is because there are more areas for expansion and the production per unit area can be improved through advance technologies.

At present, about 800 000 ha are already developed for coastal aquaculture in the Indo-Pacific region. An additional area of over 1.0 million ha is considered suitable for future development.

It should be noted, however, that aquaculture cannot be developed in the entire area. Prior to the site selection, various environmental parameters should be taken into consideration. These are, for instance, climatic condition, tidal behaviour, soil and land quality, vegetation, water quality and pollution problems.

1. OVERVIEW - S. Adisukresno (Chairman on Site Selection)

Success of aquaculture projects depends largely on the proper selection of site to be developed into ponds. During the first session, we have touched upon many aspects of the environment which need consideration. Therefore, we should now concentrate our discussions in this session more specifically on site selection.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 Environmental considerations

Prior to the site selection for aquaculture development, various environmental parameters should be taken into consideration. These are, for instance, climatic conditions, tidal behaviour, soil, topography, vegetation, water quality and pollution problems, infrastructures and socio-economic importance of the considered area. Two of these listed parameters were identified as very important common problems of the region, i.e. (1) acid sulfate soils, and (2) environmental quality and impacts.

2.1.1 Acid sulfate soils

Most of the Southeast Asian countries have large areas of coastal mangrove tidal swamps with good potential for the development of brackishwater fishpond culture. However, problems caused by the widespread acid sulfate soil in the region could have a constraining effect on the further expansion of coastal fishpond culture.

A simple, economic and rapid method to remedy the acidity produced in ponds by acid sulfate soils has been reported. This consists of repeated sequence of drying, filling, submergence, and flushing of the pond bottom with seawater, and leaching of relatively large dikes provides the remedy.

A better knowledge of the location and expanse of acid sulfate soils would help to spread the development of coastal pond culture as would a more rapid dissemination of knowledge of the methods used to ameliorate sulfate acidity.

2.1.2 Environmental quality and environmental impacts

Conservation of coastal areas is essential for the continued development of coastal aquaculture. Coastal pond culture in particular is dependent on the environmental well-being of the coastal zone. For example, coastal pond culture depends on the continued availability of fish and crustacean culture sites with good water quality and with protection from storms. In addition, coastal pond culture also depends on the coastal environment to provide it with sufficient seed for many kinds of aquaculture.

It is realized that there are increasing problems of water pollution in various coastal areas which in the near future could retard the development of coastal aquaculture. Four types of pollution which are now causing problems are siltation from forest clearance and tin mining activities, industrial wastes from agro-industries, agriculture wastes such as pesticides and peaty water, and domestic wastes from populated areas. A related environmental problem is physical damage to ponds and facilities from flooding, and poor water quality due to bad land use practices up-country from the coast.

¹ Papers contributed by participants or observers to this Consultation/Seminar (See Annex B).
² Papers read in previous meetings and or published papers that are relevant to the subject of this Consultation Seminar (See Annex C).

Attention to the environmental impacts made by users of the coastal zone is therefore well justified. These impacts include those made by coastal aquaculture itself. This is an important consideration because of the possible negative environmental impacts of one aquaculture operation on another, if they are located too close together, or otherwise compete for water, space, or seed resources. This is also an important consideration because of potential negative impacts on other uses of the coastal zone.

It is true to state that these impacts can be minimized by close attention to site selection, fishfarm design and layout, and through good fishfarm management. However, it must be emphasized that the guidelines presently available for minimizing the negative environmental impacts of coastal pond culture are not sufficiently detailed so as to be easily applied by the coastal aquaculture engineer. It is therefore recommended that steps be taken to provide coastal aquaculture planners and fishpond engineers with adequate guidelines for minimizing the impacts associated with siting and operation of fishfarms. An example of a specific need is for better criteria or guidelines to determine “green belt” widths under various coastal siting situations. Another specific need is for siting criteria for minimizing ecological damage to the most productive portions of mangrove swamps.

2.2 Site selection

2.2.1 Procedure and methodology

Broadly considered, site selection for coastal aquaculture consists of a two-stage procedure. The first stage incorporates environmental, economic, social and geo-political evaluations of geographic areas of varying size with the objective of identifying specific promising sites for aquaculture. This first stage evaluation is based largely on already available data and a minimum of field investigation. Historical data going back to 10 to 20 years may have to be considered to pin down extreme variations in some parameters such as for climate.

The second stage of site selection consists of actual field surveys of the most promising sites using detailed versions of the same criteria as listed above. The results of the field surveys are used to make the final site selection(s).

The present problem with coastal aquaculture site selection is therefore not the lack of criteria or of suitable procedures, but rather a lack of wide dissemination of the already available information in a comprehensive, manual-type format which would be pertinent for the region and readily available to those involved in site selection. An additional problem is that some important facets of sampling methodology have not been adequately treated in the detail necessary to ensure reliable interpretation of site selection measurements. Handling of soils for acid sulfate tests provides one example.

It is therefore recommended that a manual for coastal aquaculture site selection be assembled using the available reports and other background information on the subject which have been produced recently in this region. The manual should be designed to be useful regionally, and it should include detailed site selection criteria and procedures. Methods peculiar to coastal aquaculture site investigations, or methods not readily available in standard texts should be detailed in the manual, as should special equipment, including cheap, innovative equipment. Furthermore, the manual should provide means for scoring of site evaluation results for purposes of aiding final selections.

One facet of site selection on which additional work has been recommended is developing an improved method for weighting parameters and scoring. It is recognized that the relative importance (weight) of each parameter will vary according to the overall objective of the project (e.g., social welfare vs. profit motive), and according to the biological characteristics of the organisms being cultured (e.g., an organism for which high water quality is essential vs. one which is relatively tolerant). The relative importance of each parameter also may vary regionally within a country as, for example, the costs of labour and construction materials are affected by local factors of supply and demand.

One approach to the parameter weighting scoring problem is to assign relative importance weightings on each parameter as objectively as possible.

3. CONTRIBUTED PAPERS

3.1 Some notes on site selection for coastal fishfarms in Southeast Asia - R.G. Hechanova (CP3)

Some engineering problems associated with various coastal aquaculture projects in the region are reviewed and discussed. Various environmental parameters as they relate on fishpond engineering are considered and the author makes suggestions for engineering improvements associated with them.

The paper specifically discussed the need for extensive soil samplings, field and laboratory analyses. Samples are taken from predetermined soil collection sites using sampling equipment for disturbed and undisturbed samples.

The North Sumatra experience which was a case of see-page of water through small tunnels substantiated the importance of knowing the physical characteristics of soil as an independent variable in site selection.

3.2 Criteria for the selection of suitable site for coastal fishfarms - S. Adisukresno (CP6)

This paper provides details on site selection criteria and guidelines on equipment, timing and methods for on-site investigation. Criteria and scoring for four coastal fish-pond sites are tabulated for illustration.

In selecting the site for coastal fishpond construction, various properties of the proposed sites should be taken into consideration. These are, for instance, soil, land elevation, area, tidal behaviour, freshwater supply and soil pH. Some methods for on-site measurement of these environmental properties were suggested. For final evaluation, ranking and scoring of various parameters are suggested to be proper methods in selecting the best site.

3.3 Problems, field identification and practical solutions of acid sulfate soils for brackishwater fishponds — A. Poernomo and V.P. Singh (CP7)

Large areas of Southeast Asia offer attractive potential for the development of coastal pond culture; however, much of this area may be subject to acid sulfate soil problems.

Methods recently developed allow fishponds with acid sulfate problems to be rapidly improved. This paper reviews field identification and describes practical solutions for the amelioration of acid sulfate problems in fishponds.

In regard to site selection, surveys had to be conducted to produce contour and cross-section map to know the distribution of the potential acid sulfate soils in coastal tidal swamps. This data is important in making plans for proper method of reclamation. Some basic methods for qualitative and quantitative identification of acid sulfate soil were described, viz., vegetation, foaming of sulphide, H₂O₂ and pH measurement.

3.4 Engineering design and construction of coastal fishponds in Malaysia — C.K. Khoo and R. Santhanaraj (CP10)

Based on two government projects investigated by the authors who were involved in a consultancy in Malaysia, the engineering criteria for site selection were explained. The major parameters considered from this viewpoint were: (i) topography, (ii) soil conditions, and (iii) infrastructure.

Detailed topographic surveys will determine the actual level of the site and form basis for more accurate construction estimates. The soil characteristics which were examined included chemical characteristics, soil bearing pressure, strength, shrinkage and settlement condition, and permeability. Accessibility and availability of infrastructure facilities were also investigated as these are important factors for development.

3.5 Wind and wave action in coastal ponds — B. Tiensongrusmee (CP12)

Coastal breakwaters widely used in coastal fishponds to protect wind and wave action against shore facilities are mangrove buffer zones, riprapping, floating breakwaters, wood barriers, worn out tires, secondary levees and wave deflectors. To protect from wind and wave action in coastal ponds, the proper orientation of the coastal pond in relation to the direction of the prevailing wind is important to minimize the fetch or length of exposed area to wind. Other ways are by providing a wave absorber berm, riprapping the dike, installation of a pneumatic barrier, and planting trees or farm crops along the dike. The effective structures for current breakers are green belt buffer zones, jetties and riprapping.

Since there are many types of breakwater that can be used to protect from wind, wave and current action against shore facilities and coastal fishponds, it is necessary to evaluate the available types as to their feasibility, their relative effect in dampening wave energy, durability, life span and economics. The structure must be checked and modified properly by applying the most advanced analytical methods and verified by model tests.

3.6 Coastal mangrove swamps for fishponds: A focus on some environmental factors — T.L. Ti, R. bin Hassan and L.D. Rajamanickam (CP14)

This is a case study which looks at various design features of fishponds which can be improved given a specific set of climatic and acid sulfate soil condition.

The acid sulfate soil problem in the west coast of Malaysia was described.

3.7 An integrated approach to the survey, investigation and study of coastal fishpond projects — C.K. Khoo and T.O. Wuan (CP21)

This paper described an approach taken by a commercial consulting firm for the assessment of environmental and associated parameters important to coastal pond aquaculture in mangroves. This method involved a two-tier approach, the first of which was a general pre-feasibility appraisal, and the second was a more in-depth feasibility study which focused on specific sites.

The methodology developed by the authors is illustrated by application to two cases in Malaysia.

In selecting the site for aquaculture development project in the coastal area, first of all, there should be preliminary surveys on environmental properties of the proposed site. The field surveys should cover a period of at least one tidal cycle. Final selection of the site is based on various components of data obtained. This includes the cost of contruction and economic consideration.

3.8 The problem of predicting seasonal and long-term variations in parameters affecting site suitability in coastal aquaculture — J.M. Kapetsky (CP22)

Criteria and methodology for assessing aquaculture site suitability are well detailed in the literature; however, there is an apparent lack of emphasis and methods on predicting seasonal and long-term variations in some straightforward solutions to the problem of predicting such variations.

3.9 Some potential environmental effects of coastal aquaculture with implications for site selection and aquculture engineering — J.M. Kapetsky (CP23)

The negative environmental impacts of coastal aquaculture are small relative to some other destructive uses of the coastal zone. Nevertheless, attention to ways to minimize negative environmental effects is well justified, particularly in the case of the development of pond culture in mangrove and its effects on the mangrove ecosystem. Guidelines for minimizing such effects are presented which are pertinent to site selection, fishfarm design and operation.

3.10 Environmental considerations for the development of coastal fishfarms in the Indo-Pacific region — P. Menasveta (CP24)

Various environmental factors in the coastal area of the Indo-Pacific region are described. These include, for instance, climatic conditions, tidal behaviour, soil and land quality, vegetation, water quality and pollution problems. In the region under consideration, there are three types of climate, viz., tropical rainy climate, tropical savannah climate, and tropical monsoon climate. The climatic factors could give some impacts on coastal ponds in three respects, i.e., temperature, precipitation and evaporation. In this region, the tidal range is rather weak in some areas, usually not exceeding 3 m. Problems concerning soil in this region are acid sulfate, sandy and peat soil in some coastal areas. Regarding the vegetation, mangrove appears to be the most important item in the present consideration because many mangrove areas have been converted into fishponds. Care should be taken into consideration regarding the green belt. Regarding water quality and pollution problems, there are four points that should be taken into consideration, viz., siltation, industrial wastes, agricultural wastes and domestic wastes.

It is suggested that the types of areas that should be avoided as sites for fishponds are as follows: (1) site where the soil is sandy or rocky or both; (2) sites which are too elevated and reached only occasionally by extremely high tides; (3) sites overgrown with or forested with large size trees; (4) sites located in areas with very great tidal fluctuations (5 m or more) or those with very small tidal ranges (1 m or less): (5) sites located in areas with intense acid sulfate soils and containing high organic matter (peaty water); (6) sites located in areas which are very near to industrial complex zone or highly populated zone.

SECTION 2
DESIGN 1 — LAYOUT OF COASTAL FISHPONDS

Contributed Papers (CPs) — 2, 5, 8, 10, 13, 19, 20, 25, 26
Background Papers (BPs) — 2, 6, 7, 8, 10, 15, 16

1. OVERVIEW — R. Djajadiredja (Chairman)

The layout of coastal ponds varies greatly from country to country and even from area to area within one country. Indonesia, the Philippines, Taiwan (China), Thailand, etc., have their own typical pond layout and design composed of a rather complicated set-up of water supply system, series of ponds including headponds, nursery ponds, transition ponds and rearing ponds. This is also the case with the milkfish nursery system. The proper layout of nursery and grow-out ponds is essential in determining the success of coastal fishfarming. It may determine the type and method of culture techniques that can be used, the species that can be cultured, the degree of water and pond management possible, the level of production attainable and to a certain extent the economic returns from the farm. It is essential therefore to make an inventory of the layout of coastal fishponds in order to identify the most productive and economic layouts of coastal fishfarms found in each country so that we can further recommend improvements if necessary in the respective countries or for the region.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 Layout of coastal fishpond projects vary from country to country and sometimes even in different regions within one country. The most recent and most effective layout used in each country has however been identified. The essential components and details of these improved layouts are worth disseminating in the various countries in the region.

2.2 The layout can vary very much with the species used for culture. Those for penaeid shrimps will differ from those for herbivorous finfish (milkfish), and also those for carnivorous finfish (seabass, grouper). When polyculture of these species are used, more complications are introduced which would further require modifications of the layout. For example, an efficient layout for penaeid shrimp has been developed in Thailand; for shrimp/milkfish polyculture in Indonesia and the Philippines and for milkfish monoculture in the Philippines.

2.3 The type of management will also determine the kind of suitable layout that should be used for the fishpond project. Traditional types has been in existence for a long time but recently a need for the partial intensification (semi-intensive) and intensification are required in layouts suited for semi-intensive and also for intensive management. Traditional, semi-intensive and intensive models for the culture of penaeid shrimps are illustrated by Thailand while models for intensive systems for milkfish have been put up both in the Philippines and Indonesia.

2.4 Modified milkfish fingerling production system developed in Indonesia using layouts already existing and adopting modifications based on Philippine nursery complex have increased survival by 30 percent. This improved layout should be adopted more widely in Indonesia for the benefit of the industry and can also be demonstrated in other countries of the region.

2.5 Extensive modifications in layout design to maximize the efficiency of management for milkfish production has been evolved in some Philippine coastal fishfarms. The basic components of this layout with the technology for its practice is recommended for trial in other areas of the region.

2.6 The engineering expertise to develop fishpond layouts based on the requirements of the aquaculturists for more efficient management is being developed in Malaysia. If the aquaculturist can provide the basic or standard requirements for such management, the engineering sector can respond complying with the structural details and layout required.

3. CONTRIBUTED PAPERS

3.1 Observations on design, layout and construction of coastal fishponds in the Southeast Asian region — R.G. Hechanova (CP2)

In terms of layout, this report indicates that canals and ponds with regard to areas or units should complement each other. Initially before making the layout, surveys should be made to locate the paths of the natural creeks and determine the topography of the site. Also, an adequate buffer zone of not less than 20 meters from the river bank should be conserved as a mangrove area, and a buffer zone of not less than 100 meters from the seashore. The provision for the buffer zone from the river bank will provide for an idle stretch between the tidal river water source and the fishpond system. Since the river sometimes becomes turbid, this idle stretch serves as a suitable sedimentation area thus, improving the water quality.

Sluice water gate should not be close to the river intake. Good layout requires that the main gate in river-fed farms be located at the upstream of this stretch of the main canal. Generally, the main supply canal is also used as the drainage canal, transport of fish stock and materials and for harvest.

It follows that natural sites for coastal fishponds should not always be regular or rectangular in shape. In the case of the Bedagai fishpond project in North Sumatra, Indonesia, for example, in an attempt to make the ponds and the layout in rectilinear form natural creeks were closed which has resulted in serious seepage problems.

The question of size of individual compartment is dependent in one way or the other, on the amount of earth-work involved. For instance, if the pond bottom elevation has been established, then the amount of cut and/or fill can be calculated. Fill goes to diking and filling the low areas below the pond elevation and cut comes from the digging of the canals and the areas with elevation above the bottom elevation.

When machines are intended to be used in the construction, pond dimensions could be limited to the distance where this machine can work effectively. For example, the dragline can effectively and economically work in pond dimension in the multiple of 60 m (200 ft). This is because, for a 21 m (70 ft) boom, the range is 30 m (100 ft) on each side.

3.2 Aspects of design and construction of coastal ponds for milkfish seed production — R. Djajadiredja and T. Daulay (CP5)

This report lays emphasis on suitable layout for milkfish nursery production adapted under Indonesian conditions. This has become necessary because of the high mortality (50–70 percent) existing in traditional Indonesian nursery systems. An improved Indonesian nursery innovation is basically developed from that of the Philippine system combined with the typical layouts already existing in the country, namely the Jakarta type (CP5, Fig. 3). The local fry pond layout is designed for small holder farmers based on 2–3 stages of progression nursing system. This improvised system called the Kamal type resulted in 20–30 percent increase of survival of fry which is substantial when we consider that there is a shortage of fry from natural sources. This improved system is suitable for a separate nursery project or as a unit of a milkfish culture project which include the grow-out portion.

3.3 Variations of fishpond layouts for different types of brackishwater fishpond management — L.O. Alcantara (CP8)

This report based on the coastal ponds for milkfish or polyculture of milkfish and penaeid shrimps, enumerates various types of layouts which have been developed to make production management in coastal fishfarms more efficient. This is based on Philippine situation with characteristic swampland elevation and tidal behaviour.

A conventional type of layout makes provision for the three types of ponds, i.e., nursery, transition and rearing ponds in proportion of area of 1:9:80, respectively, with 10 percent being allotted for canals and other facilities (CP8, Fig. 2). All Philippine coastal fishponds are by law required to have 100 meters buffer zone along the shore and 20 meters buffer zone along the river bank. The pond system of the conventional type as well as the other systems usually adapts to the shape of the available site.

The second type of layout is the modular pond system (CP8, Fig. 3). This also provides for the necessary nursery and transition ponds but, in addition, the rearing ponds are arranged in progressively increasing areas of 1:2:4, etc., or alternatively 1:3:9. The idea in this system is to transfer stocks from the first rearing pond to the second and to the third as the stock grows and crowd themselves. In this way, harvest can be made from the terminal ponds (largest rearing pond) in a period of between 35–45 days so that cropping of over five times per year could be made from the system and production could be considerably increased.

The progressive proportion of enlargement from one rearing pond to the next has still to be precisely determined. At the moment the above figures are arbitrarily used until some standards have been established.

The third type of fishpond layout is the multiple stock/ harvest system. This system also provides for the necessary nursery ponds and rearing ponds but a new type of pond called fish holding compartment (FHC) rather than transition ponds are provided (CP8. Fig. 4). The idea is to stock in the rearing ponds which are usually longer than wide multi-size milkfish consisting of fingerlings, post fingerlings and juveniles in a pre-determined proportion simultaneously in order to fully utilize the optimum rearing capacity of these ponds. Periodic harvests between specified periods could be made by gillnet seine to catch the largest group of stock in the rearing ponds which are subsequently replenished by stock of the smaller age stage from the nurseries or the fish holding compartments. This type of layout/system is good for polyculture of Chanos.

3.4 Engineering design and construction of coastal fishponds in Malaysia — C.K. Khoo and R. Santhanaraj (CP10)

Based on two engineering contracts previously executed by the authors on Malaysian aquaculture projects, the report indicates that the layout for a coastal fishpond is based mainly on the requirements of the aquaculturists. These include for instance the rate of water renewal required which could be translated by the engineer into suitable physical structures of the project. The sizing of the ponds are also largely determined by their uses, e.g., nursery ponds are small and rearing ponds are better if larger.

On the basis of these requirements, the engineers formulated layouts for the Merbok scheme and Danga scheme in Malaysia. These projects are intended to rear penaeid shrimps mainly. Penaeus monodon and P. merguiensis as well as finfish especially the seabass, Lates calcarifer. The engineers tried to comply with the requirements for the culture of these species as given to them by the government aquaculturists.

The typical layouts in both projects provide for nursery and rearing pond systems. In the case of the Merbok project additional ponds to be used as trapping ponds were also developed. The nursery pond system normally covers a small proportion of that of the rearing ponds. The system of canals and water control gates will provide for the necessary management of water in the project. Layouts are also based on other basic studies such as tides, topography and others.

3.5 Notes on certain biotechnical problems in the layout, design and construction of coastal ponds in watershed basins with upland erosion — S. Akhmad (CP13)

This report suggests a special layout for coastal ponds in watershed basins with heavy highland erosion. Complexes of pond modules are surrounded on the sides by dikes which protect the complexes against freshwater floods. The flood protection dikes are constructed of surplus pond soil excavated to increase pond depths and sediments which settles in pond ditches.

Heavy sedimentation occuring in these watershed basins frequently clog up the inlets of rivers. Double funnel-shaped inlets for such rivers or their lateral branches are suggested to prevent the process of clogging. This is because the narrow part of the funnels would create relatively higher current speeds so that the settling of sediments in the inlet could be prevented.

3.6 The status of coastal aquaculture in Sri Lanka — V.P. Mendis (CP19)

Coastal aquaculture in Sri Lanka is just at the initial stage. There is no standard pattern of layout yet developed. The present layout of the government aquaculture station is based on the area available and the shape of the site and considering the objective that the compartments built can be used for demonstration and experiments on milkfish fry.

3.7 The present design and construction of ponds for rearing penaeid shrimps in Thailand — K. Chalayondeja, P. Tharnbuppa and S. Sigka (CP20)

Coastal fishponds in Thailand have existed for quite a long period. At present, there are about 26 000 ha of ponds devoted mainly for the culture of penaeid shrimps and the country has still some potentials for expansion in this industry. The layout of the ponds, therefore, depends very much on the management method used for the production of shrimps. There are four types of layouts existing in the country, namely, traditional, modified traditional, semi-intensive and intensive. The traditional ponds (CP20, Fig. 2) are usually modified from existing saltponds or paddy fields by merely making peripheral canals of 2 to 3 meters in width in which water of 70–90 cm in depth can be retained. There may be one compartment or more depending on the volume of water supplied from one part of the pond with the use of dragon wheel pumps located at a point along the riverside of the pond.

The modified traditional pond (CP20, Fig. 3) is essentially the same in layout as the traditional pond except that more powerful pumps were introduced mainly the propeller push pumps. This necessitates the raising of the dikes and increasing of the perimeter canals to a width of 4–6 meters with the water depth increasing to 1.5 meters. Usually in this type of layout, larger pond area is required.

The semi-intensive ponds introduced by the Department of Fisheries in 1971 are modifications from existing ponds with the addition of nursery ponds into the system. The nursery ponds are used for rearing hatchery shrimp seed. Sometimes instead of dikes, a nursery pen is built for nursing shrimp post larvae which are later released into the ponds by merely opening the pens or the dikes of the nursery compartments.

In the intensive type of layout the ponds (CP20, Fig. 5) are designed especially to rear shrimp larvae from the hatcheries. Here better means to drain and refill water so that it could be clear and new most of the time and better circulation are provided in the pond system. Nursery ponds or pens are also constructed within the rearing ponds and supplementary feeding is supplied for the stock under culture. A typical intensive farm may be 1–6 ha in area with a perimeter canal of 8–10 meters wide and with a depth of 1.5 meters. The depth of water at the berm is about 75 cm.

3.8 Present status of the brackishwater fishponds in East Java, Indonesia with emphasis on engineering related problems — M.J. Bandie, D. Tribawono, Iswahjudi and A. Sidik (CP25)

The coastal fishponds in East Java are of long existence and they have some established layout patterns. Two types are well known, namely, the Taman type and the Porong type (CP25, Fig. 4). Though differently arranged, the parts of these layout designs are essentially the same. These include strategically located control gates, well built perimeter dikes, water canal system with related catching ponds, temporary nursery compartment, and the rearing ponds.

3.9 Observations on pond design and engineering of improved privately-owned tambak in Maros, South Sulawesi Province, Indonesia — S.E. Wardoyo, M. Pirzan and R. Djajadiredja (CP26)

The paper discussed about the layout/design of two private tambaks which have been improved from the traditional system of pond layout by providing a more manageable water control system. The grow-out ponds are arranged in parallel to the water supply canal so that each compartment can take its water supply independently of the other. The nursery ponds in one of the projects are constructed temporarily on the sides of the rearing pond so that each series of nursery pond can obtain water directly from the water canal. In the other project, the nursery ponds are still constructed or located on the old traditional way, in the center of the grow-out ponds.

SECTION 3
DESIGN 2 — STRUCTURAL DETAILS OF COASTAL FISHPOND STRUCTURES

Contributed Papers (CPs) — 2, 5, 10, 12, 13, 19, 20, 26
Background Papers (BPs) — 3, 6, 7, 8, 10, 14, 15, 16, 18

1. OVERVIEW — C. dela Cruz (Chairman)

Following site selection and making layout is the design details and specifications of fishfarm components such as dikes, water control structures, channels for the water supply and drainage system, and design of pond compartments. The manner of fitting these together harmoniously in accordance with the biological requirements of the cultured species is very important in achieving the objective of creating the best environment for the animal in order to increase production.

Discussion in the design of dikes should give emphasis to the necessity of having the perimeter or main dikes and its protection if located in exposed shores; the secondary and tertiary dikes; the bases in determining their respective heights, protection from internal waves within the pond compartments, provisions against seepage or leakage and others.

For water control structures, emphasis should be on proper elevation of foundation of gates and pond bottoms, provision for piles and piling materials, determining the width of sluice and other secondary gates in relation to the tidal fluctuation and service area; use of screens, slabs and lifting mechanisms for gates.

On the channel system, consideration should be on the size of flow and conveyance of water at non-destructive velocities, the size of cross-section considering size of flow and other uses such as fish holding facility; and elevation of canal bed in relation to pond bottom elevation.

For pond compartment design, the specifications should focus on the carrying capacity of pond, the design features for various management input such as in extensive and intensive systems, monoculture or polyculture systems.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 The information on the design of dikes are well presented in the papers. The need for primary perimeter, secondary and tertiary dikes in various layouts are well recognized, including the various types of coastal breakwaters and protection works against erosion, seepages or leakages. Proper engineering design of breakwaters and its economics, however, were not covered. More specific information and design procedure of breakwaters are needed.

2.2 The various materials used in gate construction is an indication of the level of technology being applied in various countries of the region. Low input technology is generally practiced where gates are made of wood and bamboo. Permanent structures are usually used in semi-intensive and intensive culture systems. In addition, the number of gates increases to two for intensive system and the use of pumps goes with it.

The analytical procedure for determining the width of sluice gate is a little complicated for biologists to appreciate. Some effort to simplify this in form of nomographs should be done.

2.3 There are a good volume of quantitative information that have been generated empirically in the layout of ponds through years of experience. Rationalization of these empirical information to show the engineering and biological relationships is lacking and desirable to be explicitly expressed, including the assumptions used. For example, the ratio between the nursery to transition to production ponds has been determined, but the quantity of fingerlings and biomass on carrying capacity considered during the design has not been studied thoroughly.

2.4 As a whole, it is recommended to have a simplified design procedure for the fishfarm structures. Production of nomographs from design formulas would be desirable. It is recommended that a manual on aquaculture engineering for coastal fishfarms be produced in the near future. This manual should cover the whole process of applying engineering and biological principles in establishing a fishfarm. The design and construction of structures would be one of the subjects.

There are not many institutions agencies disseminating aquaculture engineering technology. It is suggested that a comprehensive training course in aquaculture engineering be designed and implemented for fisheries universities and training institutions. Such training should be given to universities or training institutions which are interested in offering aquaculture engineering or in strengthening their offerings if such already exists.

3. CONTRIBUTED PAPERS

3.1 Observations on engineering design, layout and construction of coastal fishponds in the Southeast Asian Region — R.G. Hechanova (CP2)

During visits to several established projects as well as proposed sites in Indonesia, Malaysia, Philippines, Thailand and Vietnam, the structural details of the various projects were examined. Where such structures require improvements and their reworking are possible, suggestions for making such improvements were described.

3.2 Aspects of design and construction of coastal ponds for milkfish seed production — R. Djajadiredja and T. Daulay (CP5)

The construction specifications of the various pond compartments, namely the baby box, fry ponds, transition ponds and catching ponds are given. The nature of the perimeter dikes and internal dikes are also described. Of importance for water control and management are the water supply canals and water control gates which are described with given specifications for this type of project.

3.3 Engineering design and construction of coastal fish-ponds in Malaysia — C.K. Khoo and R. Santhanaraj (CP10)

The ponds are designed to have levels based on mean sea level (MSL), uniformly at +0.50 MSL. Pond sizes depends on the purpose, namely nursery, rearing or trapping ponds. These are also limited by capacity of the heavy equipment used for construction which is the dragline.

Three types of dikes are determined — perimeter, second-ary and tertiary. Each has specific height to allow for free-board after shrinkage. Appropriate sizes and slopes of these different types of dikes are also specified.

Supply and drainage canals for water management to provide the required volume of water and rate of exchange are included. For water different types of gates are provided. namely culvert gates, open flumes with drop boards, or turn-down pipe. Structural details for each type are described and illustrated. Ancillary facilities include foot bridges, vehicular bridges, field shelters, storehouse, office and cold room facilities. Structural designs of these specific facilities for each project are also provided.

3.4 Wind and wave action in coastal ponds — B. Tiensongrusmee (CP12)

Coastal breakwaters widely used in coastal fishponds to protect wind and wave action against shore facilities are mangrove buffer zones, riprapping, floating breakwaters, wood barriers, worn-out tires, secondary levees and wave deflectors. To protect from wind and wave action in coastal ponds, the proper orientation of the coastal pond in relation to the direction of the prevailing wind is important to minmize the fetch or length of exposed area to wind. Other ways are by providing a wave absorber berm, riprapping the dike, installation of a pneumatic barrier, and planting trees or farm crops along the dike. The effective structures for current breakers are green belt buffer zones jetties and riprapping.

Since there are many types of breakwater that can be used to protect from wind, wave and current action against shore facilities and coastal fishponds, it is necessary to evaluate the available types as to their feasibility, their relative effect in dampening wave energy, durability, life span and economics. The structure must be checked and modified properly by applying the most advanced analytical methods and verified by model tests.

3.5 Notes on certain biotechnical problems in the layout, design and construction of coastal ponds in watershed basins with upland erosion — S. Akhmad (CP13)

The structure and design of “laci-bar” which can be used to prevent fishpond sluice gates from sinking if constructed on deep soft swampy foundation is described. Design of coastal pond polder complex applicable in areas where excessive flooding from the upper watershed is explained including means to prevent occasional closure of tidal creeks due to silting, by the use of constructed double-funnel structures.

3.6 The status of coastal aquaculture in Sri Lanka — V.P. Mendis (CP19)

For two government projects in the country, the structural details for the ponds, water channels, pumps, dikes and water control gates are described.

3.7 The present design and construction of ponds for rearing penaeid shrimps in Thailand — K. Chalayondeja, P. Tharnbuppa and S. Sigka (CP20)

Construction specifications are given for traditional ponds, semi-intensive ponds and intensive pond projects in Thailand. The design of the different types of ponds in relation to the water control structures, especially the pumps and water canals and gates are also given.

3.8 Observation on pond design and engineering of improved privately-owned tambaks in Maros, South Sulawesi Province, Indonesia — S.E. Wardoyo, M. Pirzan and R. Djajadiredja (CP26)

The structural details for the dikes, gates, and ponds showing the improvements over traditional types are given.

4. COMMENTS OF DISCUSSANTS

4.1 Topic 1: Design of dikes: Perimeter or main dikes and dikes along exposed shores; secondary dikes; tertiary dikes

4.1.1 L.O. Alcantara (Philippines)

The presentation described the various design parameters in the determination of main, secondary and tertiary dike heights.

For the main dike, parameters considered are the highest astronomical tide, allowance in height for wave action, soil shrinkage, settlement and freeboard.

For the secondary dike, height is determined by referring to the highest spring tide, elevation of ground surface, maximum rainfall allowance due to shrinkage and freeboard.

For the tertiary dike, the pond bottom elevation desired, depth of pond water, maximum rainfall recorded in 24 hours, freeboard and shrinkage allowance.

Calculations for height involves the use of formulas:

Main dike

Where

Hm = Height of the main dike
HAT = Highest astronomical tide
GS = Elevation of the ground surface
MF = Maximum flood level
FB = Allowance for freeboard
%S = Percent shrinkage and settlement

Secondary

Where

Hs = Height of the secondary dike
HST = Highest spring tide
MR = Maximum rainfall within 24 hours

Note:

Values of %S are:

The recommended height of main dike varies from 40 to 60 up to maximum of 100 cm higher than the highest tidal level in the area. The top width of dikes varies with its specific use. For main dike, it varies from 1.5–3.0 m, the size of which increases if designed against flooding, higher tide level and for vehicular passage. Secondary dike range from 1–2 m, and for tertiary dike, 1 m or less.

The base of dike is determined based on the side slope as influenced by the soil characteristic. The common side slope ranges from 1:1 to 2:1 (horizontal to vertical). Flatter side slope than 2:1 has been recommended for dikes exposed to severe wave action. In areas where the soil is of heavy clay, side slope steeper than 1:1 is also used. Some examples of main, secondary and tertiary dikes, and side slopes are shown in BP7, Figs. 1–3.

4.1.2 T.L. Ti (Malaysia)

Dike cross-sections are better designed where the use of berms add to protection against seepage and structural stability against settlement.

4.1.3 P. Tharnbuppa (Thailand)

In the design of dikes, stress is made on provision against seepage. The soil material must have an adequate amount of clay and shall be properly compacted, preferably by mechanical equipment as by a tractor. Excess fills are seen to be more of an advantage than a lack of it, as the excess soil material, in the maximum use of land can be utilized for growing agricultural crops. Excess fills are also made as wind barriers for ponds. This is to protect the “lablab” or milkfish food as a specific case, when there is a predominant strong wind blowing in the area. This barrier scheme is, however, thought as good for cultured finfish only but not for shrimps.

4.1.4 V.P. Mendis (Sri Lanka)

The problem of dike erosion at the sea side slope was discussed and this is due to the boats loading and unloading activities of the dike quay. The use of concrete berms and barrier has proven to be effective.

Lining of the dike sides is presented, and for seepage the solution is building another dike paralleling the existing one.

Dike protection works are discussed and these are by the use of worn-out tires, boulders placed on the sea side slope.

The varied uses of plastic sheets was discussed and the different methods of installation are presented. The economics of their uses were however set aside for later discussion.

4.2 Topic 2: Water control structures

4.2.1 B.S. Ranoemihardjo (Indonesia)

Presentation is concentrated on traditional gates made of wood, bamboo, or a combination of wood and bamboo, mainly or all of a one-opening control gate for rearing and nursery ponds. Wood slabs, if preserved against wood borers are painted with coal tar. In some ponds, slabs are made of teak wood.

Mention is made of a maximum limiting width of gate to 1.00 m. This is to provide ease in manual operation of slabs.

4.2.2 D.R. Jamandre (Philippines)

Gates must preferably have a uniform width so that slabs could be interchanged.

PVC pipes provides easy installation and a relatively long life and these pipes provide water inflow (and outflow) into ponds preferably for water exchange. The pipes are usually installed at the wooden sluice gates but may also be installed through dikes. Mention was made during the discussion about the problem of mechanical breakage in the use of PVC pipes.

The use of pipe drains with monks was also discussed.

4.2.3 C.K. Khoo (Malaysia)

The use of PVC pipes is limited where ultraviolet light destroys the material. When used to provide adjustable control of the water surface by providing a 90-elbow, there is the added problem of leakage.

Screens are of several materials, design and configuration. If bamboo screen is used, this is made of split bamboo woven according to what size of splits is needed. An “umbrella” type of bamboo screen easily fits into a small pipe culvert.

A method of providing a small bore (hole) on the slabs, permits a pipe to be fitted into and this could regulate the flow and allow excess rainwater to pass through the pipe.

4.2.4 K. Chalayondeja (Thailand)

The purpose of sluice gates are given as follows:

1. To receive the sea water as well as natural seed.
2. To manage the level of the water in the pond.

3. To facilitate harvesting.

The traditional shrimp pond has one gate made of wood having a size of 0.75–1.00 m wide which is appropriate for a pond of 3–8 ha.

For intensive pond, it is necessary to have two gates made of concrete or cement blocks with reinforcement. The size is about 1 m wide but some ponds have larger gates about 2 m wide, divided into two portions. This size is suited for a pond area of 1–4 ha.

The pond can receive water through the sluice gate during spring tide in about 3 days, and later on water is supplied into the pond by using pumps.

4.2.5 V.P. Mendis (Sri Lanka)

The water control structure in Sri Lanka which is usually made of brick rubble and concrete are presented. The design structure has been shown in CP19.

4.2.6 R.G. Hechanova (Philippines)

The presentation focused on minimum design requirements for gates such as the determination of the width of the sluiceway, depth of cut-off wall at both upstream and downstream sides, length of the floor and of the transition wing walls, for permeable and inpermeable foundations.

Mention is made of the need to have the elevation of the gate bottom well below the lower low water in the area.

A basic design scheme was also presented for a gate made of brick.

An overview of the analytical design computations for the determination of the width of the sluiceway as presented in the report is made.

4.3 Topic 3: Channel or canal system design

4.3.1 R.G. Hechanova (Philippines)

The economic consideration for design and design for hydraulic efficiency of open channels or canal systems are discussed. Some of the basic principles presented are:

1. Where the water cross-sectional area is minimum, the flow velocity is at maximum.

2. Widening the canal bed is more preferable than increasing the depth of flow in canal for a given discharge and velocity.

An allowance of 20 percent for water loss during conveyance from the source to the serviced pond area is mentioned

4.3.2 S.R. Suyanto (Indonesia)

The depth and the width of canal are designed in accordance with the tide condition and the pond areas. For Indonesia, the Government does the plan in constructing the main and secondary canals for the fishfarmers under subsidized scheme. For the tertiary canals the farmers have to construct these by themselves.

4.3.3 P. Menasveta (Thailand)

Three types of open channel for supplying water to ponds were tested for a high density — intensively fed prawn farm, viz., an earthen channel, channel lined with plastic sheet and a concrete channel. It was found out that the concrete canal had many advantages over the other types, namely; it lasts longer, no leakage, and less friction. The only disadvantage was due to its high cost of construction. Water is supplied to the mentioned open channel by a Thai made propeller suction pump.

4.3.4 D.R. Jamandre (Philippines)

Due to the increase in construction costs and the limited area available, there seems to be a trend towards smaller units in an aquaculture set-up. These smaller units (5 ha or less) give the pond operator more flexibility where management and marketing are concerned.

Experience with shrimp culture indicated that ponds have to be designed with two gates: supply and drainage gates. A peripheral canal around the pond bottom and a canal from the supply to the drainage gates also serve as sheltering canals for the shrimp.

The pond bottom slopes toward the drainage gate and facilitates water movement for water change or harvests.

It was suggested that for small aquaculture farms using pumps, small open channels running along top of dike for water supply may be used.

4.3.5 V.P. Mendis (Sri Lanka)

Channels in his station is small and has problem of erosion. To prevent such erosion, timber planks are used to riprap the side of the channel. Since tidal range in Sri Lanka is small, complete drainage is hardly done.

4.3.6 T.L. Ti and C.K. Khoo (Malaysia)

It is emphasized that in order to have proper design of the water channel the engineers need to have some information on the culture scheme and method of operation of the system. The engineer has to know among others the volume of water required, the frequency and methods of water change. The basic criteria for designing the water channel are the following:

1. Rate of flow needed to fill the pond; and

2. Volume of water required.

It is mentioned that all standard design tables for open channel is based on constant head flow and steady flow. For coastal aquaculture, tidal flow is that of unsteady flow type and therefore has to be treated as such. Design of sluice gates should use the principles of unsteady flow.

The solution in determining the proper width of sluice gate is by iteration process and it is a little complicated.

4.4 Topic 4: Design of pond compartments: for penaeid shrimps, for finfish or for various polyculture systems

4.4.1 K. Chalayondeja (Thailand)

Improved design of conventional shrimp farm is given. The farm is about 3.2 ha (20 rai) consisting of a nursery pond of 0.32 ha and rearing pond of 2.88 ha. The pond has two water control structures approximately 1 m wide each. With this type of water control structure, the pond can be gradually filled within 4–5 days by gravity flow. Inside the pond is a peripheral canal about 3–4 m wide and 1.5 m deep. By extensive culture system, the improved shrimp farm can yield a production of P. monodon about 80 kg/rai/year or 500 kg/ ha/year.

Ponds for intensive culture system is also discussed. The pond is about 6 ha with 8–10 m wide of peripheral canals and 1.5 to 1.8 m deep. This type of rearing pond has a nursery pen made of fine meshed enclosure net. The proportion of nursery pen and rearing pond is 1:100, respectively. The stocking density of post larvae (PL 15–20) is 20 pieces/m². The production of 1 000–1 500 kg/ha/year with average size of 33 g of P. monodon can be obtained.

4.4.2 L.O. Alcantara (Philippines)

Modification of the conventional type into radiating management of ponds used in the Philippines is presented. The advantage of this modification is economy in dike construction. The diagonal or radiating layout of dikes is recommended for semi-circular shape or square shape site of production ponds.

4.4.3 T.L. Ti and C.K. Khoo (Malaysia)

Water exchange in the shrimp pond system is emphasized. Two projects in Malaysia are presented — the Merbok and Sungei Danga Brackishwater Aquaculture Development Projects of the Fisheries Development Authority of Malaysia (LKIM), in which different water supply systems resulted in the pond design.

The ponds of Merbok Brackishwater Aquaculture Development Project is designed for water supply through gravity flow. This pond system is designed based on the criteria that the water change of the whole pond is at least one-third of the volume per week. The depth of pond is 0.6 to 0.8 m. However, based on the practical experiences obtained, it is indicated that for proper water management and good growth of shrimp, the water change should be at least one-third its volume daily and not weekly.

The Sungei Danga scheme was designed for water supply system maintained partially by tidal action and supplemented by pumping. This combination is arrived at due to presence of natural water courses which allow only 60 percent of the low area for development and therefore higher areas are also considered for development. An alternative design is considered whereby pumping is eliminated by lowering the pond bottom elevation but this resulted in the overall project cost to be higher by approximately 20 percent.

To have total harvesting of shrimp, it is suggested that a catching pond should be designed and incorporated into the design.

4.4.4 A. Poernomo (Indonesia)

Most of the Southeast Asian countries mainly Indonesia have vast areas of coastal mangrove tidal swamps potential for the development of brackishwater fishpond culture. However, the problem paused by acid sulfate soil found in this area could be a constraint.

A simple, cheap and rapid reclamation method has been developed to remedy the acidity produced in acid sulfate ponds. The method described in this paper consists of repeated sequence of drying, filling, submergence and flushing with the water of pond bottom and leaching of relatively big dikes. The whole workplan of reclamation is preferably done during dry season for rapid pyrite oxidation.

SECTION 4 DESIGN 3 — CONSTRUCTION METHODS OF COASTAL FISHPONDS

Contributed Paper (CPs) — 2, 10, 19, 20, 25
Background Paper (BPs) — 1, 7, 8, 15, 16

1. OVERVIEW — C.K. Khoo (Chairman)

In this Section discussions should emphasize on details of mechanized construction, manual and traditional construction methods in the countries of Indonesia, Malaysia, Philippines, Sri Lanka and Thailand.

Pre-construction planning identifies the different activities involved and the determination of what particular activity precedes or follows another with reference to a time frame.

The choice of construction plan and equipment whether for mechanized or manual methods of construction is necessarily dictated by economics and for this, technical considerations and the nature of the project must be analyzed in order to reduce the cost of major construction items, e.g., earthwork and water control structures.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 The choice of manual, mechanized construction or a combination of both is dictated by the economics and technical consideration of construction depending on the construction method.

2.2 A construction schedule is needed to further strengthen and make effective planning before and during any construction is started. This is done using a table or a bar graph which lists and indicates the number of days needed and spent in each case. A typical programme chart is indicated in Annex A.

2.3 Earthwork computations are basic to any plan for fishfarm development, as other activities, like planning a layout for example, is dependent on earthwork.

2.4 Use of improved methods of manual labour will continue to be useful such as finishing work in construction. It is noted that the number and quality of available, skilled manpower for the work is declining in many countries in the region, and so there is a need for further training and finding means of making the remuneration for this type of specialized labour attractive.

2.5 The use of the flatboat was very well discussed and its use is well justified in the manual method of construction.

2.6 It has been identified that most of the equipment being used in mechanized fishpond construction were not designed for the specific work involved. Fabrication of machinery suited for work in the environment for coastal fishfarm will be needed and should be encouraged.

3. CONTRIBUTED PAPERS

3.1 Observations on engineering design, layout and construction of coastal fishponds in the Southeast Asian Region — R.G. Hechanova (CP2)

Due to the high construction costs, many coastal fishponds in the region are built in phased out manner up to the joint when the farm can operate, and further improvements are later done from the earnings of the farm. First, the site is marked off and the location of water control gates and various ponds are determined. The path of the dikes are thoroughly cleaned before actual construction.

Various digging implements are used in the different countries where manual method is used and in addition carrying soil blocks for the dikes by use of flatboat has been initiated and is widely used in the Philippines. Water control gates along the main dikes are constructed at the same time as the dikes.

Construction by the use of mechanized heavy equipment were seen in Malaysia and Singapore and to a lesser degree in Thailand. Draglines and power shovels have been proven to be most suitable for earthwork. Sporadic use of mechanized method met with difficulties with some and other with success in the Philippines. Low ground pressure (LGP) swamp dozer tried in the Philippines was found difficult to operate on soft ground. For lack of available skilled labour, mechanized equipment continue to be used in Malaysia and Singapore. The dragline mounted on mat of logs which may be cut from the project site is generally used as platform for the operation of this heavy digging equipment. Most of these mechanized heavy equipment have specific range for effective operation which can limit the shape and sizes of pond compartments. The escalation of oil price limits pond construction by machines, but their use becomes a necessity where there is no available skilled labour for this work.

3.2 Engineering design and construction of coastal fish-ponds in Malaysia — C.K. Khoo and R. Santhanaraj (CP10)

In Malaysia mechanized construction is preferred due to labour shortage which has caused rising of wages. Other factors are the scale of project and tide conditions which render labour intensive methods impractical.

Low ground pressure dozers (LGP) or swamp dozers appear suitable for dozing felled trees and tree stumps. Draglines are used to grub up tree stumps. Collection of felled tree stumps and roots is difficult as movement of machines in swamp is slow. LGP dozers work economically for travel distances of 40–50 m.

For construction of ponds, dikes and canals the draglines operating on timber mats is considered to be the most suited for earthworks. This type of plant is versatile and has sufficient reach for excavation and filling and also has the capability of forming and trimming regular side slopes for canals and dikes. Pond design should take into consideration the need to minimize movement of soil over long distances to avoid multiple handling. Compaction is done by construction in layers and the dragline travelling on the dike as the work progresses.

For water control structures excavation is either by drag-line or backhoe on tracks. Bakau piles are driven to pre-determined lengths with motorized piling rigs and concrete structures are cast in situ using a mechanized concrete tipper mixer.

Machine clearing of site has been carried out at a rate of 10–15 ha per machine month and earthworks have been excavated at a rate of 4 000 m³ per machine month.

3.3 The status of coastal aquaculture in Sri Lanka — V.P. Mendis (CP19)

The brackishwater fisheries stations have been established in lagoon tidal flats and swampy areas in Sri Lanka.

Clearing of swamp areas for pond construction is generally carried out in the dry season to facilitate disposal and burning. Trees are felled by using axes and knives. Manual digging is done with the help of an equipment similar to a hoe. Compaction is achieved by a mallet-like implement made of wood.

Special care is taken to store the top soil initially and eventually it is spread over the pond bottom.

3.4 The present design and construction of fishponds for rearing penaeid shrimps in Thailand — K. Chalayondeja, P. Tharnbuppa, S. Sigka (CP20)

The method of construction to a large extent in Thailand has been manual in the construction of the four types of ponds, viz., traditional, improved traditional, semi-intensive and intensive. Traditional method includes the use of hoes for construction of ponds.

Thailand in recent years has embarked on mechanized construction methods especially for the construction of canals to supply seawater to the brackishwater ponds along the coastal regions. In this project, tractors and backhoes are the equipment adapted for construction. Excavation using manual method have resulted in earthwork in the order of 10 m²/man day working 6–8 hours/day.

3.5 Present status of the brackishwater fishponds in East Java, Indonesia — M.J. Bandie, D. Tribawono, Iswahjudi, A. Sidik (CP25)

The traditional manual method of building fishfarms is still in practice, where a group of 3–5 workers are hired on a piece work basis.

For the construction of dikes, the profile of dikes is set-up using bamboo or timber and a puddle trench is excavated to secure a good anchorage for the dike. For excavation of the soil, a hoe or digging blade called “sarab” or “lempa” is used. Water control structures are generally constructed of re-inforced concrete, timber or bamboo.

Suitable cover crop, e.g., dampalit or krokot is planted at the top and side slope of the dikes to prevent erosion. Often other cash crops are planted on dikes to supplement income.

4. COMMENTS FROM DISCUSSANT

4.1 Fishpond construction — Philippines (L.O. Alcantara)

Manual construction of brackishwater ponds has been widely carried out in the Philippines due to high cost of machine hire.

Traditionally, trees are felled and pulled down manually and to some extent small machines have also been adapted for this purpose.

For excavation of the soil for ponds and canals and the construction of dikes, digging blades have been used. A flat bottom boat is used to transport blocks of excavated soil for dike construction. An average of 6–7 m³ of earth can be moved per man-day working 8 hours/day.

Water control structures are generally of reinforced concrete, but timber and rarely bamboo constructions are also used.

ANNEX A
A TYPICAL PROGRAMME CHART IN THE CONSTRUCTION OF A COASTAL FISHFARM¹

1 Source: BFAR FAO-UNDP, Philippines, Fishfarm Engineering Manual. pp. 59–61.

SECTION 5
DESIGN 4 — REPAIRS AND MAINTENANCE OF COASTAL FISHPONDS

Contributed Papers (CPs) — 2, 4, 15
Background Papers (BPs) — 2, 6, 8

1. OVERVIEW — K. Chalayondeja (Chairman)

Maintenance and repairs of coastal fishponds and other piscicultural facilities contribute to the success of fishpond culture.

Environmental factors have great effect on the pond such as wind, rain, poor soil quality, damage caused by organisms, corrosive effect from salt water. Immediate attention should be given to leakage/seepage, erosion of main, secondary, tertiary dikes, wooden gates or concrete gates including accessories, screens and slabs. Other facilities in the pond that need attention are nets, digging tools, water pumps, etc. Maintenance and repairs are very important work of the fishfarmer to be considered carefully in order to maintain the ponds in good condition and derive better yield. It is, therefore, worthwhile discussing the reports from different countries which will contribute useful information for the region.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 Maintenance and repairs of coastal fishponds play an important role in brackishwater pond culture. Seepage, leakage and erosion of dikes must be repaired by manual labour or through mechanization if the area affected is extensive. To prevent erosion of dikes along coastal fish-ponds, mangrove buffer zone, log barriers, and other protective facilities must be installed. Suitable creeping grass are also planted on the dikes.

2.2 Water control gates, particularly wooden secondary/ tertiary gates are often damaged by wood borers and other organisms. To some extent, oysters and barnacles deter water current flow through the gates and must be scraped periodically. Paints mixed with anti-fouling and other preventive/ preservative solutions should be used to paint the wooden structure gates.

2.3 A fishfarmer must be a keen observer on any untoward happenings in the fishpond which he must attend to immediately.

2.4 Elevated thick soft mud or sedimentation can be removed or levelled with long wooden planks or bamboo rakes. Several kinds of tools implements can be used by manual labour to remove accumulated mud on the pond bottom. Muck pump may also be used in narrow channels and canals with soft muddy and elevated bottom.

2.5 Equipment and tools used in the coastal fish/shrimp culture ponds should be properly maintained to attain much longer use. Logbook is recommended for proper care and maintenance of the major equipment.

2.6 The rate of evaporation and precipitation as well as other untoward loss or increase of water in ponds should be studied as these have great effects on piscicultural management.

3. CONTRIBUTED PAPERS

3.1 Observations on engineering design, layout and construction of coastal fishponds in the Southeast Asian Region — R.G. Hechanova (CP2)

In this paper, the author firmly believes that equipment/ tools in brackishwater ponds must be properly maintained. He further elucidated the use of logbook for each mechanical equipment such that proper upkeep can be fully attained and ultimately will lead to the much longer use of the equipment/ machinery. Safety measures of engines on their proper use must not be overlooked.

Channelization/canal construction may increase erosion if there is an abrupt increase in gradient. It may cause serious problem on the slope of dikes.

3.2 Maintenance and repairs of established coastal fishponds — B.S. Ranoemihardjo (CP4)

Maintenance and repairs of coastal fishponds play an important role in brackishwater pond culture. Pond compartments and canal system should have proper water control structures. Pond preparation in relation to water management will enhance better growth of natural food. Seepage/ leakage at the time pond bottom is being dried will adversely affect food growth. This condition usually occurs if the soil blocks laid along the dike are improperly laid. Besides, poor compaction of the soil will naturally cause seepage. Leaks/ seepages can be controlled by plugging the source with arenga fiber together with clay soil.

Equipment and other fishpond paraphernalia must be kept properly at all times and ready for use when needed. Usually, tools/equipment commonly used for maintenance in ponds are as follows: digging blades, shovels, mud scoops, spades, bancas and various kinds of nets.

3.3 Equipment and facilities for coastal fishpond construction, maintenance and repair — C. dela Cruz (CP15)

For maintenance and repairs various types of soil excavation and transferring equipment should be available in the fishfarm. Leaks and seepage of dikes are corrected by digging puddle trench and refilling with new soil using local digging blades. Dikes should be planted with cover crop of grass or other vegetation but overgrowth of these cover plants should be cut manually or by portable grass cutters or tractor mowers.

To insure continuing good water quality and availability as well as for draining, use of pumps may be required. For this operation, low-load discharge type or propeller/axial-flow type pump driven by motor or electric power can be used. Basic equipment for water quality monitoring, such as those for measuring pH, dissolved oxygen, salinity and turbidity can be useful for proper fishpond management.

Effective use of gate screens with the water control gates or pipes should be practiced. Sealing the gates with soil seal between wooden slabs, in properly spaced grooves provided during the gate construction, can be useful as management tool during the drying of the pond or if controlled watering is desired.

4. CONTRIBUTIONS FROM BACKGROUND DOCUMENTS AND DISCUSSANTS

4.1 Dike erosion

Coastal fishponds are subject to strong waves due to exposure from the open sea or bay and cause erosion to the main dike. To minimize the effect of the waves on the dike, buffer zones with mangrove trees act as wave breakers. Other protective covers for the dikes are breakwater made of handlaid boulders on flat side slopes, by bamboo pilings at the dike toe on the seaside, jetties, wave deflectors, floating bamboo/wood/log barriers, worn-out tires tied together to form a raft-like structure, protective levees of “spur-dikes”, etc.

During heavy rains, newly constructed dikes are subject to erosion. This can be prevented by planting suitable creeping grasses such as the African stargrass (Cynodon plestostachus) or plants that can grow on slightly acid or salty acid soils.

4.2 Leaks and seepages

These situations occur through the dike due to improper methods of construction (laying of soil blocks, poor compacting of soil), or caused by boring organisms like certain crustaceans and poor soil quality. Control of leaks/seepages can be implemented by excavating a puddle trench with digging blade, spade or other digging devices along the mid-portion or along one side of the dike. Plastic sheets are stretched and laid properly/perpendicularly to the bottom of the trench and subsequently filled up with clay or clay loam soil.

4.3 Gates

Concrete gates are most often covered with barnacles or oysters and may cause impediment to the flow of water in and out of the pond system. These are periodically scraped off with digging blade, spade or equivalent.

Wooden gates are likewise attacked by barnacles, poly-chaetes, wood borers resulting in greater depreciation. Immediate repair and installation of wooden gate must be initiated so that pond management will not be affected. Prior to installation of the repaired wooden gate, it must be painted with coal tar or creosote mixed with copper oxide.

4.4 Pond bottom

The canal system of a fishfarm most often becomes shallow due to sedimentation. Periodic desilting of this waterway with muck pump will bring about better efficiency to pond water management.

Uneven pond bottom requires longer period of preparation of the pond for the growing of natural food. Cut and fill process of levelling the pond bottom may be instituted by using flat bottom boats for transporting soil from the higher portions to the low areas. In small ponds or canals, a muck pump could be used in soft bottom soil. Soft muddy bottom from high portions can easily be scraped with long wooden planks and/or straight logs.

4.5 Screens and slabs

Gate screens and slabs sometimes break due to water pressure and may cause loss of stock or undesirable predatory species of fish may enter the pond. The use of double screen offer a back-up for safety against loss. If these screens are not in use, they are air-dried and kept in the storage room for equipment.

4.6 Equipment and other fishpond paraphernalia

Machineries and other fishpond paraphernalia have to be properly maintained and ready for use any time. Equipment made of iron or susceptible to corrosion or rust must be washed with freshwater after use in the pond. These are allowed to dry and rub immediately with oil or grease. A logbook of operation and maintenance should be accomplished for the machineries.

Fishpond nets of various sizes must be properly dried and stored when not in use in the storage room.

SECTION 6
DESIGN 5 — EQUIPMENT AND FACILITIES FOR COASTAL FISHPOND MANAGEMENT

Contributed Papers (CPs) — 1, 2, 4, 11, 15, 18
Background Papers (BPs) — 1, 7, 8, 9, 17, 18

1. OVERVIEW — S. Akhmad (Chairman)

In comparing the various equipment, tools and implements used by coastal fishpond operators in the region, it can be observed that there is great variety in these equipment mainly based on local tradition, different developmental stages and production aims of the coastal fishpond industries of the various countries. Thus, for instance, the production of protein food produced mainly on natural food is being done in the ponds of the Philippines and Indonesia. On the other hand, high-priced crop of fish and shrimp is being produced in Thailand ponds by using marine trash fish as feed. The task of this Section is to look into the various equipment and facilities that could be useful for more efficient management of coastal fishfarms.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 As most fishfarmers in the region are small-scale operators, attempt to develop pond management equipment should be based mainly for the purpose of improving the lot of these operators. Whenever possible, the equipment to be used should make use of inexpensive indigenous raw material, so that small-scale operators will be able to acquire them. Investigation on and the identification of the most efficient equipment should be made to be recommended to the numerous small fishfarmers in the region.

2.2 Most of the equipment being used in mechanized fishpond construction were not designed for the specific work involved. Fabrication of machinery suited for work in the environment for coastal fishfarms will be needed.

2.3 Research on alternate energy sources such as wind, tidal and solar energy should come up with appropriate technology for coastal aquaculture. This has assumed greater importance at present because of high fuel costs.

2.4 Much local improvements in the fabrication and renovation of push pumps from available equipment parts have been attained in Thailand. Studies should further be made to determine the most economical design for a more efficient operation of push pumps.

2.5 When using aeration by paddlewheels to improve dissolved oxygen levels in ponds, water current and wave action resulting from the aeration should be taken into account. Dissolved oxygen levels should be monitored. More research on improving the design and efficiency of aeration devices should be made.

2.6 Removal by hand of mud settled in pond ditches is inefficient. The unacceptable and slow method used to do the job justifies the use of sludge or muck pumps. The possibility of pumps for hire should be considered since operators would need these gear for only relatively short periods.

2.7 The use of screens at pond gates to minimize the entry of predators into the pond should be suited to the size of the species under culture. However, care should be taken that the placements of screens should not obstruct the flow of water and cause erosion of perimeter dikes near the main gates.

2.8 Equipment for harvesting ponds should be designed to facilitate good quality harvests. Present methods of harvest include seine nets and on larger ponds, propeller-driven suction pumps and propeller-driven boats with trawl net attachments. Studies are needed to determine the efficiency of various harvesting methods aimed at further improvements or fabrication of new and more efficient equipment.

2.9 Greater use of feeds is increasing and will further expand in the future. Inexpensive equipment for the manufacture of feeds such as solar driers and others should be investigated.

2.10 Designs for suitable transporting vessels suitable in fishfarm environments should be investigated. These may include boats for transporting fertilizers to the farm or fish from the ponds.

2.11 Investigations into economic and effective fencing materials to keep out predators such as snakes, lizards and otters should be undertaken. Suitable designs for security facilities should also be made available.

3. CONTRIBUTED PAPERS

3.1 Pumps for coastal aquaculture — D.R. Jamandre (CP1)

The selection of the material for pump construction is at least a compromise between the cost of manufacture and the anticipated maintenance and operation costs. The paper presented a review of pumps which have been recommended for aquaculture. It includes a description of the pumps characteristics and features. The selection of the pump pumping system should be made on a case to case basis depending on the characteristics of the area and the conditions under which the pump is to operate. Using suitable parts available locally or in the market, pump assemblies suitable for specific fish-farms using certain species and type of management may be fabricated by the engineer.

3.2 Observations on engineering design, layout and construction of coastal fishponds in the Southeast Asian Region — R.G. Hechanova (CP2)

Various equipment for different needs in the fishfarm including those for survey and monitoring, construction, repair and maintenance are mentioned and their uses explained.

The amount of silt load carried by the stream during normal and flood flows have to be eliminated using proper equipment such as the muck or sludge pump.

Fabrication of suitable equipment, if necessary, may be required. Use of indigenous material is advisable.

3.3 Maintenance and repairs of established coastal fish-ponds — B.S. Ranoemihardjo (CP4)

A short review of the indigenous implements was made by the author. These implements are used in the maintenance and construction of ponds. A brief comment was made regarding the rigging of outboard motors propeller for moving water in tide-fed ponds.

3.4 Paddlewheel aerator for emergency pond aeration — P. Menasveta and P. Leeviriyaphanda (CP11)

Organic matter accumulation on the bottom of ponds during high density/intensive culture of shrimps, prawns or fish reduces the dissolved oxygen available to the animals under culture.

A description of the construction and the cost of paddle-wheel mechanical aerator for shrimp and prawn ponds was presented. Experiments confirming the effect of aeration were carried out and data was presented. Paddlewheel pumps are used for 5 to 6 months in Thailand, and a paddle depth of 25 cm was found to be the best for aerating the ponds.

3.5 Equipment and facilities for coastal fishpond construction, maintenance and repair — C. dela Cruz (CP15)

Equipment/facilities for water control included pumps, screens and water sealed gates were described.

To monitor pond conditions, methods and equipment to determine pH, salinity and turbidity were explained.

Fertilizer platforms which have been found effective for prolonging the fertilization process were also discussed.

3.6 Water pumps in shrimp farms in Thailand — P. Tharnbuppa (CP18)

Water supply problems for Thailand's coastal ponds necessitates the supplying of water under tidal conditions of low amplitude by using pumps. Four types of pumps were presented: the dragon wheel pump, the push pump driven by diesel engines, combinations of push pumps for sea water and pressure pumps for underground freshwater, and push pumps driven by electric motors. These pumps are assembled in Thailand using imported used engines and other parts. The economics and installation processes for the four systems were discussed.

4. CONTRIBUTIONS FROM DISCUSSANTS

4.1 Equipment used for the maintenance of pond structures

In the Seminar, attention was focused on the stopping of the dike leakages and the reclamation of pond depths.

Interest was generated during discussion on the use of plastic sheets to prevent and mend leaks in dikes. The sheets were to be set lengthwise in the middle of the dikes and should reach the clay core previously set in the base of the dikes.

Various digging tools used in the region to reclaim pond depths were described. Descriptions were also given for Philippine flatboats and Indonesian bamboo rafts which are used to transport excavated pond soil to deposition sites.

Due to the fact that sedimentation supply ditches frequently shallow up, to maintain the depths of these ditches, pond operators drag and pull a 3–5 wide teak board through the sludge on the bottom and, subsequently the accumulated sediments are removed from the ditches.

4.2 Pond irrigation equipment

Pumps recommended for aquaculture uses were reviewed in the Seminar. Included in the review were descriptions, characteristics and features of pumps.

Criteria for the selection of pump systems were also outlined. However, it was thought that selection would at best, be a compromise between manufacturing costs and anticipated maintenance and operating costs of pumps.

Furthermore, it was thought that the selection should be based on a case to case basis, depending on the characteristics of the sites in which the pumps are to be installed and also on the conditions under which the pumps are to operate.

4.2.1 Dragon wheel pumps

These are still used by pond operators who stock their ponds with shrimp fry present in the inshore waters. The wooden buckets or troughs of the pumps do not supply large amount of water to the ponds. However, they facilitate the entry of shrimp fry into the ponds by scooping them up from the water of the supply channels.

4.2.2 Propeller push pumps

Water supply for Thailand coastal ponds necessitates the supplying of water under tidal conditions. The descriptions, installation and economics were given for push pumps powered by diesel engines and electric motors as well as combinations of sea water push pumps and freshwater pressure pumps.

In Indonesia, a simple propeller pump consists of a boat propeller placed inside a motor drive propeller. Since propeller pumps mechanically lift water by the pitch of the propeller in each revolution, the thrust bearing must absorb the entire accelerating force created by the impeller.

Speed on propeller pumps is limited by the cavitation at the propeller tips. Since the tip velocity increases with the diameter, the larger the propeller diameter, the slower it must turn.

Some considerations in the design of pumps include the calculation of the brake horsepower (BHP) which is inversely proportional to the source of the internal diameter of the pipe.

The tangential velocity is limited by cavitation. The bigger the diameter, the slower it must turn for the same volume of discharge.

The use of a gear drive or pulley changes the rpm requirement and also gives better mechanical ratio. The elbow must not be more than 45°, preferably much less.

Equipment used in ponds deteriorate due to physical, chemical and biological factors present in the environment. By applying proper maintenance procedures, such as covering sluices with paint or other preservatives, and greasing engines regularly, life times of equipment could be extended. The keeping of logbooks may help in prolonging the use of these equipment.

4.3 Equipment to monitor and maintain soil and water quality

Pond water should be of proper quality. Thus, determination of pH, salinity and turbidity are necessary. Descriptions on how to determine these parameters were presented.

Maintaining proper amount of dissolved oxygen is very important especially in the high density intensive shrimp ponds where high amount of organic matter accumulate and reduce the available dissolved oxygen. Paddlewheels as used in Thailand may solve this problem. Descriptions of the construction and cost of this aeration equipment were presented. Comparative experiments on unaerated and aerated ponds were also described and the data were presented.

Aerators can be used to supply air for intensive culture ponds. Aeration also facilitates the creating of water current for circulation of water.

Pond soil and water fertility should be maintained if high production rates are to be reached. Fertilizer platforms are used for delaying the solution of fertilizers so that their supply to pond waters could be extended.

4.4 Predator control equipment

Screens are used to control the entry of predators, their eggs and fry into ponds with incoming tides. Comments were made on the installing of the screens, since these structures slow down the flow of water into the ponds. Improper installations may also cause erosion of dikes within the boundary of sluices.

Care should also be taken in selecting the proper mesh sizes as shown in the table below.

4.5 Alternate energy sources and utilizing appropriate technology

At present there is a vast storage of information on the practical uses of power from wind, sun, tides, etc., for providing the energy to run pumps, process feeds and in general, lower the amount of high cost energy input into the operation of the fishfarm industry.

The use of wind power will require the survey and collection of wind velocities data over a period of at least a year. This is to determine what months of the year wind power is usable. Collection of the data on the amount of sunshine available shall also be made over at least a year. Perhaps, these data can be obtained from the Weather Bureau or Meteorological stations near or at the farm site.

The selection of the most appropriate design of the equipment should not be limited to only a single design as many other designs may be available. For example, computerized bibliographies can simplify and speed up literature searches for such designs.

SECTION 7
ECONOMICS, CONSTRAINTS AND PROGRAMMES IN THE ENGINEERING OF COASTAL FISHPONDS

Contributed Papers (CPs) — 5, 10, 18, 19, 20, 21, 25, 27
Background Papers (BPs) — 1, 4, 7, 12, 15, 20

1. OVERVIEW — T. Banerjee (Chairman)

One of the major problems presently confronting the development of coastal aquaculture in the region is the high initial development cost of fishfarms due to significant charges from site survey and selection, structural design and construction of the required facilities. The progressing state of the art is however, such that there should now be options to suit each kind of investment in ensuring the viability of the chosen fish culture system. The interrelationships between the development cost and the annual gross return for each of the existing systems of culture, are unfortunately unclear as a result of a general lack of comprehensive economic information on these practices. Under the circumstance, the planning and implementation of the development of coastal aquaculture are being adversely affected. There are at the same time inherent technical problems and other shortcomings which must be overcome before major development programmes could be effected.

2. CONCLUSIONS AND RECOMMENDATIONS

2.1 General observations

From the results drawn from experiences of existing national development programmes and bilaterally and multilaterally financed projects, coastal aquaculture is widely considered to have considerable development potential in the region.

Especially under the present circumstance where there is a tendency for national fishery yields to be on decline, the development of coastal aquaculture could in fact provide feasible alternative engagements to the numerous poverty-stricken, socially depressed coastal fishing communities. Hopefully, it could also make up the shortfall in fish supply.

The generally low state of the art for the domestication of very little understood, wild marine and brackishwater organisms, tends to suggest however, that there will arise increasing problems in the planning and implementation of this development. Given such limitations, it is not surprising today, more than ever before, for investors to take much more cautious steps towards feasibility assessments of their investments. As often as not, team approach is stressed involving biologists and engineers of various fields.

To gather sea life is not economical below a certain size and concentration of animals at any level of technological sophistication. A similar situation often occurs in aquaculture when cost and earnings fail to strike a happy balance. Whatever this balance may be, production performance must not fail to attract new investments and to justify the continuation of investments already made.

There should be hundreds of thousands of hectares of mangrove swamps and mudflats for the development of coastal fishpond culture in the region; but unfortunately only a small percentage of this resource is being utilized. Apart from conservation reasons, this is largely due to the low productivity of traditional culture systems practised in these coastal ponds.

With the recent advances made in coastal aquaculture development, it is now possible to introduce new systems of culture, and to improve existing culture practices through team approach in development, in which the contributions of fishpond and environmental engineers are indispensable. To accelerate this development, it is vital prerequisite that economic answers be made available to facilitate development planning, especially in the identification of constraints and the means to overcome them.

It would appear that information on the economics of coastal aquaculture is indeed very little known. The economics for the engineering aspect of coastal aquaculture is another unknown which must be discovered as expediently as possible. Three cases of the economics of culture farms were offered by the discussants, which served to at least indicate the order of benefits of these situations.

2.2 Problems/constraints

In coastal pond culture of shrimp and finfishes, one actually confines dense stocks of wild marine and brackish organisms in “selected man-made” bodies of water. Such a confinement often creates ecological stresses on the fish stock, deprives the species of its optimal conditions for survival, and accelerates the spreading of diseases and fluctuation of vital environmental parameters. Under the circumstances the stocked fish often suffer mass mortalities and/or stunted growth.

This is further complicated by a number of human and inherent factors arising from biased and or invalid site selection criteria and production management, making it difficult to almost impossible to approach the estimated yields.

If viability is what an investor or rural fishfarmer needs, the assurance of the control of these variables and uncertainties must be necessity be of priority to the biologists and engineers. Without such an assurance, there would be no investments in coastal aquaculture, and rural fishfarmers would be a liability more than anything else. Some level of technological sophistication is therefore, required to facilitate development. The following prevailing constraints in the region must be resolved with the assistance of the engineers.

1. Acid sulfate soil. To a greater or less extent, this problem is region-wide. When its adverse effects express themselves, almost instant mass fishkills become inevitable. The control of such situations will no doubt be a priority economic consideration.

2. Water system. As a rule of thumb, the faster the turn-over of water in a pond, the better the growth of the fish and the higher the fish yield. Fast-flow water system is however, difficult to design resulting from various limitations such as acid sulfate soil, varying tidal characteristics, energy and equipment cost, and other direct or indirect economic and technical factors.

3. Increasing yield. This objective is perhaps the only way to ensure the viability in aquaculture investment. In addition to solutions to (a) and (b), the problem in the supply of seed and feed must be resolved as a matter of priority. As long as economics permits, new investments especially from the industrial sector should aim at semi-intensive to intensive systems of culture.

2.3 Programmes

In a nutshell, the design of a programme of work aiming at the above noted situations and problems, hinges around the economics of each of the existing culture systems on the one hand, and the future market demand of the species under culture on the other. With this in mind, the following programme of work is presented in the form of recommendations from the discussions.

2.3.1 A region-wide economic and market survey of the principal and potential crustacean and finfish species currently under culture be conducted as soon as possible.

2.3.2 A region-wide cooperative study of acid sulfate soils be implemented as soon as possible with the object of coming up with effective controlling measures on the one hand, and the mapping of all developable areas in accordance with the presence or absence of acid sulfate soils on the other.

2.3.3 In considering water systems, apart from costs, the engineer considers the most economic flow-rate that would carry the optimum fish biomass without losing out on growth. Thus, in a design of water system, it can be taken into consideration all water quality problems and the biological needs of the species.

2.3.4 To facilitate increasing yield, artificial feed research and development be taken up as a priority cooperative regional programme to pave the way of future development of culture systems.

2.3.5 Cooperative artificial fish propagation programmes be carried out also as a matter of priority.

2.3.6 Under the above programme, a regional training project be formulated to assist the development of technologists, technicians and other cadres of personnel engaged in these work.

2.3.7 For development planning purposes, a workshop or seminar on aquaculture economics in the region be held as expediently as possible. In this workshop, all systems of crustaceans and finfish culture especially at the small-scale be included.

3. CONTRIBUTED PAPERS

3.1 Aspects of design and construction of coastal ponds for milkfish seed production — R. Djajadiredja and T. Daulay (CP5)

This paper reviews the experience on the innovation of an improved type of nursery pond incorporating features of the local and Philippine designs. The authors contend that with the better designed and constructed nursery facilities, an improvement of 20 percent in fry survival could be achieved. On a national scale, they have translated this improved survival rate into an additional stock of 94–110 million fry for the country. This increase in survival should significantly contribute to the betterment of the economics of the nursery of milkfish fry. The authors have likewise, offered in Table 4 of the paper the cost of construction of the nursery fishponds at 1982 costs totalling Rp 3.6 million¹ for a one-ha nursery. This information should be extremely useful at least as a reference.

3.2 Engineering design and construction of coastal fishponds in Malaysia — C.K. Khoo and R. Santhanaraj (CP10)

The authors present a case study of the engineering aspects of coastal fishpond development in Malaysia, taking as example two recent projects, i.e., Merbok Scheme (Kedah) and Danga Scheme (Johore), for which they have been commissioned as engineering consultants. The total cost of these projects of the type mentioned is high, ranging from M$20 000 to M$50 000² per hectare. These charges include site survey and selection, layout and design of fishponds and the construction of all the prescribed facilities. The major portion of this cost has however, been taken by earthworks and water control structures which constitute 50–60 percent of the total cost. Mechanized construction is preferred in Malaysia in view of the shortage of labour and high cost of wages.

¹ Rp (Rupiah) 650 = US$ 1.
² M$ (Malaysian dollar or ringgit) 2.3 = US$ 1.

These are essentially mangrove swamps. The initial development of the Merbok, Scheme, including a hatchery, covers 200 hectares, while the Danga Scheme involves only an area of 40 hectares. The economic feasibility of these two projects has yet to be seen. The organisms for culture are of the high value category including Penaeus monodon, P. merguiensis and the seabass Lates calcarifer.

3.3 Water pumps used in shrimp farms in Thailand -P. Tharnbuppa (CP18)

The author clearly states that shrimp cultured in traditional tambaks in Thailand operating on the recruitment of wild fry can be made more productive by the use of pumps. Pumping can render the management of pond water more effective. It can also pump into the tambaks shrimp fry to maximize stocking densities. He describes four different types of pumps used in Thailand together with a comparative listing of capital, maintenance and fuel consumption costs. These are the dragon wheel pump (US$867.69), the push pump driven by diesel engine (US$1 184.70), the push pump driven by electric motor (US$1 904) and the combination pump (US$2 419.40). These costs include an engine, fittings and accessories, installation, annual fuel consumption, annual repair and maintenance.

3.4 The status of coastal aquaculture in Sri Lanka -V.P. Mendis (CP19)

This paper describes the technical aspects of two brackish-water fisheries stations of the Sri Lankan Government. The inherent constraints and areas with potential for aquaculture development have been identified. Efforts by the Government to develop aquaculture is, however, hampered by the lack of financial and technical ability. The funding of the development of aquaculture would need to compete with other national activities, e.g., agriculture, in accordance with other national activities, e.g., agriculture, in accordance with priorities.

3.5 The present design and construction of ponds for rearing penaeid shrimps in Thailand - K. Chalayondeja, P. Tharnbuppa, S. Sigka (CP20)

The authors present a summary of the current design and construction of coastal fishponds for the rearing of penaeid shrimps. Resulting from development efforts primarily concerned with the artificial propagation of the cultured species, four principal shrimp culture systems have evolved, viz., traditional, modified traditional, semi-intensive and intensive. Depending upon the availability of shrimp larvae from hatcheries for repeated stocking and harvesting, yield rates of these systems range from as low as 25–90 kg/ha/year for traditional ponds to as high as 1 000–5 000 t/ha/year for intensive culture methods. Structurally, the high-yield types of ponds require better water drainage systems, larger and stronger dikes, provision of pumps, greater amount of fresh trash fish, and generally much higher costs for these and other essential inputs. A comparative study of the economics of these four systems of culture is unfortunately not made available, so that it is not possible to further examine into the prevailing situations. Throughout the text is economic information presented, though on an ad hoc basis, is useful to at least appreciate the costs of some of the inputs.

3.6 An integrated approach to the survey, investigation and study of coastal fishpond projects - C.K. Khoo and T.O. Wuan (CP21)

This report contains a description of the procedures used by the authors to assess the viability of sites for aquaculture development. They began conducting a general pre-feasibility appraisal of various pre-selected areas of the study zone. They then utilized the weighted point system devised by Jamandre and Rabanal (1975) to identify the site in each zone of study with the greatest potential for a thorough investigation by a team comprising of aquaculturists/ecologists and engineers/hydrologists. The recommendations of this technical team were subjected to further evaluation by socio-economists, management and financial experts. All findings were then integrated into a report presenting background information and environmental conditions of the study sites, the proposed pond systems and engineering works, the recommended farm management procedures and finally financial analysis.

3.7 Present status of the brackishwater fishponds in East Java, Indonesia, with emphasis on engineering related problems - J.M. Bandie, D. Tribawono, Iswahjudi and A. Sidik (CP25)

In this paper, the authors provide an overview of the role of the government in improving the economic status of the fishfarmer. Attempts of the government to foster aquaculture development by building hatcheries and demonstration ponds, providing credits and executing training programmes for fishfarmers, were highlighted.

For East Java, the average income of fishfarmers has increased from Rp 21 012 in 1975 to Rp 111 923 in 1981. Within this generalization, the 1981 average annual income of fishfarmers engaging in traditional culture system was at Rp 31 358, but in semi-intensive culture at Rp 201 461. Although it is not clear as to the profit levels of these two systems of culture for the lack of economic data, it would appear that both economic improvement and technological advancements have already been made.

3.8 Economic constraints on small/medium scale shrimp hatchery industry (Case of P.T. Benur Unggul, Indonesia) - Z. Iskandar (CP27)

The paper describes a package project funding scheme which include training component for both technical and managerial aspects. The financial and work responsibilities of the participants are described. Typical project costs were gathered for this type of project which shows over 90 percent is required for capital costs and less than 10 percent for working capital. Training and technical guidance are provided by government administrative and research agencies. Notwithstanding the social orientation of this undertaking, actual problems and constraints in its implementation are encountered and explained.

4. COMMENTS FROM DISCUSSANTS

4.1 Case Presentation 1: The cost and earning of a fresh-water giant prawn farm in Thailand - P. Menasveta

This presentation involves a case of a subsistence-level, family-sized farm using intensive feeding, high density stocking culture method. The total water surface area of the pond is 1 hectare. The development of this farm is assisted by a loan which necessitates an annual loan repayment of US $688; and the period of repayment is 10 years.

Note: The amount for amortization and depreciation were not included.

4.2 Case Presentation 2: The cost and earning of a family-sized semi-intensive penaeid shrimp farm using natural seeds in Thailand - K. Chalayondeja

This presentation again involves a case of a subsistence-level type of family-sized farm. The culture system can be classified as semi-intensive though the stocking material depends on the wild fry. If hatchery fry were used, PL20–25 of Penaeus monodon would cost at 154 pieces/US$1, and of P. merguiensis at 230 pieces/US$1. According to the given calculations about 222 250 pieces of PL20–25 would be required costing US$966. The land in this case is self-owned. Again, amortization and depreciation have not been taken into consideration.