PART I
SUMMARY REPORTS OF PANEL SESSIONS AND SECTORAL MEETINGS

SESSION 1
ENVIRONMENTAL CONSIDERATIONS - PHYSICAL ASPECTS

Overview - R.H. Gedney

The topic is physical aspects of the environment with respect to aquaculture. This can be divided into three main categories:

1. The effects of external impacts of environmental forces on aquaculture;

2. The internal impacts whereby aquaculture affects other activities; and

3. The physical aspects of the environment which affect aquaculture such as climate and hydrology.

Under (i) matters such as the effects of land reclamation and various kinds of pollution from man's activities are considered. Under (ii) are adverse environmental effects of aquaculture on man's activities, as for example flooding at mouth of rivers caused by fishpond dike construction or loss of mangrove swamps caused by fishpond construction.

1. Fishpond Development and its Relation to Drainage and Flooding - S.S. Basa (Philippines)

   The Pampanga river delta and the Candaba swamps in the Philippines is an example of the importance of proper engineering for the watershed in which aquaculture, agricultural development and urban areas need water and at the same time are suffering the effects of flooding. The delta includes 40 000 hectares of milkfish ponds which produced 32 400 mt in 1975. A large amount of this fish is marketed in Metro Manila. The area however suffers severe flooding caused by heavy rainfall. It has a large watershed of 179 000 ha and poor drainage. Flooding has been aggravated by obstructive construction of fishponds in river channels which restricted flood flows. Flood damages occur at least annually and sometimes more often causing destruction of dikes protecting farms and urban areas and also loss of many fishpond structures. Sedimentation creates unfavourable conditions both for fish and agricultural production. Persons suffering flood damages upstream become very hostile to the downstream fishpond owners and the Government even resorted to blowing up illegally constructed fishpond dikes to reduce flooding.

   A comprehensive plan has now been prepared which will greatly reduce upstream flooding and yet accommodate the downstream fishfarm owners. The plan also provides for major improvements in the socio-economic status of fishfarmers and low-income farmers in the floodplain.

2. Engineering Considerations in the Release of Mangrove Swamps for Development into Fishponds - A.R. Gatus (Philippines)

   The conversion of mangrove areas into brackishwater fishponds resulted in a loss of the mangrove swamps as a natural resource. These swamps serve as nursery grounds for aquatic juveniles, as a source of forest products and as buffer zones against wave erosion and coastal flooding. Exploitation of this resource is already extensive in the Philippines and Taiwan, China, but is still minimal in some other countries in Asia.

   The government of the Philippines has now formulated policies governing the release of mangrove swamps for fishpond development. Environmental impact studies are now required before permits for such development are allowed. The criteria used in identifying areas suitable for brackishwater aquaculture include topography, vegetation, reliable supply of fresh and brackishwater, drainage, soil characteristics, biological characteristics and other related matters. Areas which are not found suitable for fishponds are held as preserves. The primary engineering consideration is the development cost and determination of economic feasibility. Other considerations include the analysis of the total effects of fishpond development on the coastal areas. These measures are reducing mangrove swamp destruction in the Philippines.

3. The Effects of Reclamation and Coastal Development on Aquaculture Development and on Existing Projects - P.S.L. Ma (Hong Kong)

   In Hong Kong, land area is very limited and there are many active land reclamation projects. At least fifty have been underway over a period of many years. The reclaimed areas are being used for human settlement and development of industrial infrastructures. These projects affect coastal fisheries through:

   1. loss of shallow inshore sea and inter tidal areas which are rich in fauna and are major nursery ground for commercially exploited species;

   2. pollution effect of the reclamation process on the adjacent sea area;

   3. destruction of the seabed through activities associated with land development projects, such as dredging and spoil dumping.

4. Effects of Various Physical Factors in Aquaculture Production - W.G. Yap (SEAFDEC)

   Factors affecting fish production under this topic are identified as climatological and physical relating to water quality, temperature, salinity, turbidity, light intensity, wind, evaporation and precipitation. In the analysis of these factors, stress must be given to the extremes and the frequency of occurrence of these extremes. This is more important than normal situations. Biological factors related to these aspects have high variability in terms of fishery system responses with respect to matters such as growth, food production, reproduction and related matters. Proper engineering is essential in order to realize the best possible or practicable biological environments.

Summary and Recommendations

Summary

The Workshop participants all recognized good and bad environmental impacts caused by aquaculture or effects on aquaculture of other present day economic activities, with major emphasis on the following matters.

1. Uncontrolled brackishwater fishpond development in the estuaries of large rivers can cause major upstream flooding and sedimentation affecting both farm lands and urban areas.

2. Indiscriminate loss of mangrove swamps for brackishwater fishponds can create coastal erosion and ecological damage to fish and animal resources harboured in the natural mangrove environment. However, properly designed pond projects built in suitable sites can be a real benefit, if the possible environmental impacts are considered in the planning stage.

The session also noted that climate and hydrologic site properties are most important, not with respect to average conditions, but with respect to frequency of deviation from the norms. This should be considered in site selection and management planning.

Recommendations

There was a broad consensus that these impacts should be more thoroughly evaluated and studied to avoid serious and costly mistakes in the future. Detailed area-wide studies by expert group, perhaps through external assistance, should be made for areas designated as focal points of fishpond development.

References

Contributed Papers (CPs) 3, 6, 15, 24 and 28
Background Papers (BPs) 1, 2, 3, 4, 6, 8, 12, 14, 16, 21, 23, 24, 25 and 27

SESSION 2
ENVIRONMENTAL CONSIDERATIONS - CHEMICAL ASPECTS

Overview - W.L. Chan (Hong Kong)

There is a dynamic inter-action and intimate inter-relationship of physical, chemical, biological and pollution parameters in culture media. Under the circumstances, it is by necessity important to adopt a collective, systematic approach in both site selection and the management of culture media.

1. Water Quality Considerations in Aquaculture - R.R. Platon (SEAFDEC)

   This topic has reference to external and internal factors in water quality considerations. External factors include (a) by-products and wastes resulting from urbanization; (b) agricultural pollutants such as pesticides and fertilizers; (c) industrial wastes from pulp mills, sugar and oil refineries and textile plants, and heavy metals; (d) radioactive wastes from nuclear plants; and (e) oil pollution arising from navigational activities, and spillages of varying magnitudes. If not properly controlled, these may incur adverse effects on culture systems. Such situations may range from fish diseases, increased oxygen demand, public health hazards, poor product qualities, excessive loss of fish stocks, etc. The Laguna de Bay lake can be cited as an example of nutrient pollution in which the limiting factor governing the elevated trophicity was considered to be nitrogen rather than phosphorus levels. The possibility of bio-accumulation of mercury was also noted. The source of this metallic contaminant was believed to be derived from volcanic eruptions.

   Internal factors are diverse in variety ranging from the dynamics in waste decomposition to the accumulation of metabolites. These can only be controlled through the improvement of culture systems, proper management of water recycling system and engineering back-up in the design of tanks and aeration system. The inherent fish diseases, pathogens and other associated problems should be given appropriate research and development input, since these can incur direct and indirect losses to the operators.

   Discussion

   Several aspects of water quality and its importance to aquaculture were brought up for discussion. In considering water hardness, the group reached a common view that hardness had been found to have incurred adverse effects on the growth of crustaceans (e.g., Macro-brachium spp.). On pesticides the Indonesian experience was related to the group to the effect that they had been found to be a major constraint to the aquaculture industry in the lower reaches of rivers in Java and in certain parts of Kalimantan. It is recognized that the public health aspects on use of organic wastes need further study. It was unanimously agreed that a long-term study of water quality should be conducted in this region for each of the principal culture systems with a view to establish reliable guidelines for site selection.

2. The Problems of Acid Soils - A.S. Camacho (Philippines)

   The problems of acid sulfate soils in coastal swamplands, as in the Philippines, were presented and current remedial measures such as liming and chicken manuring were discussed. The effects of acid sulfate soil on dikes, dike erosion due to the absence of vegetation, leaching, increased water acidity and turbidity, and their interference with fish respiration and siltation, were noted. Some successes have been attained in growing Bermuda grass on dikes of ponds with acid soils. As a continuation of the acid sulfate soil research of UPBAC, a project proposal outlining a work plan for research has been submitted to an international funding agency.

   Discussion

   The ephemeral nature of liming, and the relationship of acidity to pond size and the water depth were discussed. The removal of the top soil in the initial excavation was thought to be the cause of high acidity in the UPBAC ponds. This was however, not the case in some private ponds. A member of the Western Visayas Federation of Fishfarm Producers, Inc. narrated his experience on how he overcame the acid sulfate soil problems in his ponds. It was generally agreed that in overcoming these problems the top soil must be preserved and the ponds limed and manured with organic fertilizers. For ponds in estuarine swamps, it was suggested that the successive application of washing and drying may be sufficient to rectify the salinity and acidity problems.

3. Soil Quality Consideration in Aquaculture Site - S. Reyes (Philippines)

   Based on experiences in the Philippines, an informative account was presented on soil quality and the predictability of seepage quantities, erosion, settlement and stability failure. The attainment of such predictability requires proper approaches, knowledge of the material properties and evaluation.

   Discussion

   The budgetary constraint of building a strong and perfect pond according to its precise engineering specifications was noted. The majority of the participants felt there should be a budgetary limit bearable by the ordinary farmers. A regional project was therefore considered necessary to gather field and laboratory data relevant to soil quality and characteristics in relation to design. The assembled information could then be used to compile a manual with recommendations applicable to the majority of regional aquaculture projects.

4. Chemical Aspects in Integrated Animal Husbandry/Aquaculture Projects - P. Edwards (AIT, Thailand)

   The future potential of an integrated animal husbandry/aquaculture system in Thailand, based on studies being made in Israel was discussed. The salient features of such a system were highlighted. In particular, organic manure was considered a good low-cost source of fertilizer for the culture of low food-chain fishes. The inherent problems arising from the application of raw organic wastes are, however, an area which requires both biological, engineering research and public health inputs. The dynamics of the ecosystem, particularly involving the adverse effects of high BOD loads and the digestion of raw animal wastes should receive priority considerations.

   Discussion

   A detailed exchange of views took place on the dynamics of the aquatic environments utilizing animal husbandry/aquaculture systems. The inherent problems of the systems were considered to merit regional research efforts.

Summary and Recommendations

Summary

Arising from the discussions of the Workshop, there are major environmental constraints prevailing in the region in connection with site selection for the introduction and/or development of various systems of aquaculture. For any one of these systems, the magnitude and nature of such constraints vary from country to country and from area to area within a country.

A thorough multi-disciplinary understanding of the environmental aspects of potential and existing aquaculture sites is therefore, a matter of high regional priority, particularly in relation to the attainment of long-term national policy objectives in aquaculture and associated supporting technological development.

The immediate problem areas as discussed at the Workshop are concerned with:

1. the need for information on the range of upper and lower tolerance levels for each main aquatic parameter vital to the optimal survival of each of the principal culture species of fish, crustacea, mollusc, etc.;

2. the need to overcome limitations of acidic soils in both pond development and subsequent pond water management;

3. the need for guidelines for the management of organic fertilization, and of integrated animal husbandry/aquaculture systems;

4. the need for measures to be introduced for the control of mercury contamination and any other metallic contaminants that may exist that pose potential threats to aquaculture systems in the region; and

5. oil pollution in Malacca Strait was noted as an increasing problem affecting fisheries. Hong Kong also noted problems related to oil pollution and it is anticipated that these problems will tend to increase in the future.

Recommendations

The Workshop recommended that:

1. attempts be made to explore the possibility of compiling information on the tolerance level for each major environmental parameter for the culture of each of the principal species of finfish, crustacea and other cultivable resources;

2. the problem of acid soils be investigated as soon as possible;

3. increased use of integrated animal husbandry/aquaculture systems utilizing waste recycled organic material is desirable; and

4. in-country and regional measures are necessary for oil pollution control.

References

Contributed Papers (CPs) 8, 9, 10, 12, 17, 23, 24, 29, 30 and 32
Background Papers (BPs) 2, 3, 5, 7, 9, 10, 11, 12, 13, 18, 21, 22, 23 and 27

SESSION 3
SITE SELECTION AND SURVEY OF AQUACULTURE PROJECTS

Overview - T.J. Jamandre, Jr. (WVFFPI-Philippines)

Considering the time, effort and amount of investment needed in venturing into any aquaculture enterprise, a proper evaluation and study is necessary in selecting the site where such projects are proposed. Site selection may be classified under several categories. Environmental considerations to be taken into account are whether the project is intended for freshwater, brackishwater or marine operation. Under each of these environmental categories are the different species to be cultured which have individual and specific requirements to simulate its natural environment under controlled conditions. Another basis of site selection to be considered is the culture technique employed, whether the project is intended for hatchery, nursery or rearing ponds.

1. Site Selection for Freshwater Projects - N. Rudayat (Indonesia)

   The factors to be considered in the selection of sites for freshwater aquaculture projects follow:

   1. Quality and quantity of water supply for stagnant ponds or running water projects. Parameters to be considered are pH, temperature, dissolved oxygen, rate of volume flow, and the possibility of pollution.

   2. Type of soil. Clay soil is preferable to sandy bottoms.

   3. Topography and elevation of site. A 5–10° slope and elevations of 50 to 800 m above sea level are considered ideal.

   4. Accessibility to market, transport, communication have to be considered.

2. Site Selection for Brackishwater Projects - K.S. Oetomo (Indonesia)

   The principal criteria which need to be verified follow:

   1. Vegetation. The types and density of existing vegetation in the locality in order to determine the cost of clearing, Different types of vegetation serve as indicators for the type of soil.

   2. Elevation and topography of the land. Swamplands in which elevations are within reach of ordinary tides are most suitable.

   3. Type of soil. Porous sandy soil should be avoided; 30 per cent clay of alluvial origin is preferred.

   4. Adequacy and quality of water supply. The site should have an adequate source of water. The water supply for milkfish culture should have a salinity of 5 to 30 ppt and temperature of 27° to 32°C; for shrimp culture a salinity of 10 to 25 ppt and a temperature of 28–31°C.

   5. Tidal range. Areas where the tidal fluctuation range between 1.5 to 2.5 m are most suitable for both milkfish and shrimp culture.

   6. Availability of fry for stocking. In order to have continuous operation, the availability of fry for stocking the project should be assured for the entire year.

3. Site Selection for Hatcheries - Fresh, Brackish and Marine - B. Tiensongrusmee (Thailand)

   In order to operate a hatchery project, the following factors have to be considered. The specific requirements for a successful hatchery operation are dependent upon the species to be propagated and the location of the physical plant. The criteria to be considered are:

   1. availability and constant supply of broodstock for continuous operation of the hatchery;

   2. for a shrimp hatchery, the sea water should be of adequate volume and with minimal turbidity and there should also be a sufficient amount of fresh water for laboratory use;

   3. since the larval stages to be produced in the hatchery are delicate animals to handle, the physical plant of the hatchery should be accessible by land, sea or air to minimize the hazards of transport.

4. Site Selection for Freshwater Open-Water Projects - V.N. Alferez (SEAFDEC)

   The primary factor to consider in the selection of a site for freshwater, open area projects is the type of holding structure to be operated. At present there are two types, namely the fishpen and the fish cage. The different considerations to be verified are:

   1. for fishpens, the depth of water should range from 2 to 3 m and for fish cage culture, from 4 to 12 m;

   2. clay loam bottom soil is preferred;

   3. topography of adjacent areas;

   4. circulation or presence of any current movement in the vicinity helps in aerating the water;

   5. the project should not be susceptible to either industrial or agricultural pollution;

   6. sufficient natural and supplementary food for the cultured species should be available;

   7. nearness to market for convenience in selling pen or cage products;

   8. availability of fry or fingerlings for stocking the projects;

   9. source and availability of ice for preserving products;

   10. availability of management and skilled labor;

   11. social conditions in the locality.

5. Site Selection for Marine Open-Water Projects - H.C. Lai (Malaysia)

   The main points stressed were as follows.

   1. The site to be selected should preferably be in a cove protected from wind and wash of waves.

   2. Freedom from pollution. The site should be away from industrial and sewage discharges to prevent mortality due to low dissolved oxygen and incidence of disease.

   3. A tidal range of 1 meter would be satisfactory.

   4. A current flow of 0.5 meter per second is desired.

   5. The site should be close to the source of stocking materials - fry or fingerlings.

   6. The optimum salinity range depends upon the species to be cultured, for grouper culture, 31–32 ppt is needed.

   Discussion

   The Chairman thereafter called for discussion from the floor especially with regards to oysters, cockle and mussel culture.

   On oyster culture F.O. Ng (Malaysia) stated that in Sabah, East Malaysia oyster culture is being developed. In the selection of site for oyster culture the following criteria are considered:

   1. ample tidal flow should be assured to prevent accumulation of metabolites;

   2. pollution - the site should not be affected by pollutants; and

   3. salinity - oysters can withstand lower salinity of water.

   He further mentioned that cockle culture is practised in many coastal areas of West Malaysia. The sites for this type of openwater culture are soft surface mud with a hard undersurface. Suitable sites are those protected from shifting due to winds and waves.

   W.G. Yap (SEAFDEC) commenting on the selection of suitable sites for green mussel culture mentioned the following considerations:

   1. availability of seeds from native broodstock;

   2. presence of natural growth of mussels in the locality;

   3. uniform relatively high water salinity;

   4. good amount of particulate organic nitrogen; green turbid water is an indication for presence of food; and

   5. absence of possible sources of pollution.

   S. Tamiyavanich (Thailand) enumerated the factors considered in selecting sites for cockle culture in Thailand as follows:

   1. salinity of water should be within 18–30 ppt;

   2. mud is preferred for type of soil;

   3. mud flats should have a gentle slope; and

   4. the area should be away from sources of pollution.

6. Types of Surveys Needed - H.R. Rabanal (SCSP)

   Unlike limnological and oceanographic studies which have established standard survey methods, surveys for aquaculture development has not yet been established. In aquaculture there are several types of surveys needed to be undertaken, such as:

   1. cadastral survey - to delimit an area and prevent encroachment and overlapping of properties;

   2. topographic survey - to identify suitability of site and levelling or excavation needs;

   3. biological survey - to acquaint us with the flora and fauna of the site which may be affected and which may later affect future management;

   4. water supply survey - to determine the adequacy and quality;

   5. soil survey - to determine if quality is good for diking and as substratum for the ponds after construction;

   6. total watershed survey - to determine the overall environmental impact of undertaking the project with particular reference to flooding upstream and in the drainage basin.

7. Pointers on Some Survey Techniques - R.G. Hechanova (FAO/UNDP-Philippines)

   The necessity for cadastral, topographic and drainage basin survey was reiterated, similarly the importance of water supply and water quality tests were noted.

   Particular emphasis was given to the importance of a survey of the soil characteristics of the site before development. Visual inspection and collection of samples should precede the making of laboratory tests. There are limited numbers of laboratories with facilities for the required tests for soils. In the Philippines, such tests can be done by the Bureau of Soils of the Department of Agriculture and the Materials Control Laboratory of the Department of Public Highways. At site, standard penetration tests are done in connection with collection of samples for mechanical analysis. Soil texture is determined by standard tests upon which the soil suitability for fishpond purposes is judged. Such characteristics as plasticity index and shrinkage index are also very important in determining suitability of soils in prospective aquaculture sites for fishpond dikes as well as characteristics of the pond substratum. Tables and nomograms developed from soils analyses of soils for proposed sites and fishponds can be used by extension workers once the proper relationships have been determined.

   Knowledge of hydraulics can be used in determining water management in existing fishponds. Practical tables have been developed for carrying capacity of trapezoidal water supply canals, for submerged culverts and for water inlet and outlet pipes. Likewise, these developed tables can be used in establishing the proper operation of fishponds.

Summary and Recommendations

Summary

Major factors to be considered in all aquaculture projects are quantity and quality of water supply, topography, vegetation, soil types and proximity and access to markets. The tidal range, coastal erosion and presence of acid soil are particular matters for evaluation in brackishwater projects. In the case of rearing ponds, availability of fry or fingerling is important. Other factors such as infrastructure, electricity and social structure must also be considered.

Recommendations

Standardized methods of site selection should be formulated for the different aquaculture projects. Methods of rating and evaluating prospective sites should be developed. While the factors to be considered may be the same from place to place the relative weights of each may vary from one country to another and from one place to another in each country.

References

Contributed Papers (CPs) 4, 5, 7, 8, 11, 14, 15, 16, 18, 19, 22, 23 24, 25, 26, 28, 29, 31, 32, 33, 34 and 35
Background Papers (BPs) 1, 4, 6, 8, 14, 22, 24 and 27

SESSION 4
ENGINEERING DESIGNS FOR FRESHWATER AQUACULTURE PROJECTS

Overview - P.E. Osborn (FAO/UNDP-Philippines)

The topic is design of various broad systems applicable to aquaculture, divided into four main categories, as follows:

1. the design of fishpens and cages;

2. modification of ricefield layout for rice-cum-fish culture;

3. design of ponds for freshwater aquaculture;

4. design of system for integrated animal husbandry-cum-fish culture.

All of the above were discussed considering project designs suitable in freshwater situations.

Category (i) was subdivided into pens used in freshwater fish and prawn culture and into cages used in freshwater fish culture under various conditions. Under (ii), a design used in ricefield fish culture indicated some modifications necessary to adapt from rice to rice-cum-fish culture. Category (iii) focused attention on problems usually encountered while in (iv) we have an overview of the many types of animal husbandry-cum-fish culture systems.

1. The Layout, Design and Construction of Freshwater Fishpen Projects - V.N. Alferez (SEAFDEC)

   Commercial culture of the milkfish (Chanos chanos) in pens in various parts of Laguna de Bay lake in the Philippines started in 1972. The pens of various physical shapes are built of bamboo and wood frames. They may be of single or double enclosures of synthetic netting which are either braced on one or both sides. These designs have been evidenced as incapable of withstanding the strong wind force, wave action and thrusts of the drifting water hyacinth. The existing design of the double enclosures is modified by joining them with horizontal components to improve the rigidity so that forces acting on them can be transmitted horizontally and vertically.

   The construction method was also improved in two ways, viz. by staking the bamboo poles for firm joining and by installing pegs for fastening with polyropes or rubber strips.

2. The Designs of Fish Cages Used in Freshwater Aquaculture - D. Sodikin (Indonesia)

   Culture of fish in Indonesia in both floating and bottom cages is practised in many provinces in order to implement the national goal of annual fish consumption of 29.5 kg/capita and to increase export of ornamental fish. The fish species under cultivation are Ophicephalus sp., Leptobarbus sp. and Cyprinus carpio while the ornamental species include Botia macrocanthus and Balanteochilus melanopterus. The production of fish per crop is 8–60 kg/m³.

   The cages measure around 2.5 × 1.5 × 1 m³ and have the framework and screening made of bamboo and wood material fixed with zinc nails. They are stabilized in water by fastenings to floating logs and they are usually equipped with enclosed square opening on the top for disposal of human wastes. Cost of construction is variable depending on the size and material, ranging from Rp 15 000–44 000¹. Cages have to be movable in order to avoid the occasional change of pH along the coastline.

¹ Rp or Indonesian rupiah; Rp 415 = US $1

3. Modifications in Layout and Construction of Ricefields Utilized for Fish Culture - K.S. Oetomo (Indonesia)

   Criteria for site selection for paddy-cum-fish culture should be based on the availability of adequate good quality water supply, suitable topography on gentle slope and proximity to human settlements.

   Modifications adopted to the existing ricefields include the following categories, i.e. the construction of stronger and higher dikes meeting the minimum specifications of 0.5 m in height and width, the provision of sluice gates and ditches measuring 0.5–1.5 m in width for efficient drainage; and installation of inclined water pipes for filling the fields.

   After harvest the irrigation conduits and the surrounding ditches of the fields are first repaired, followed by improvement of the dikes so that the lowest portion can hold water up to depth of 1 m. Leakage should be observed and avoided.

   There is a nation-wide need for development of integrated paddy and fish culture to maximize the economic returns. To meet this end, planned irrigation development and controlled application of pesticides are essential.

4. The Design of Freshwater Pond Projects with Emphasis on Problems Encountered - R. Bala (Malaysia)

   There is a large potential for aquaculture in Malaysia. To encourage easy development, design of freshwater pond projects is standardized. The construction methods are simple. The layout of a prawn and fish culture project was described and the following points were emphasized:

   1. adequate water supply;

   2. provision of efficient drainage system for execution of individual management procedures;

   3. the attention to soil quality and soil mechanics;

   4. good roads and access both inside and outside the farm.

5. The Design of Various Types of Integrated Animal Husbandry-Cum-Fish Culture Projects - M.N. Delmendo (FAO/UNDP-Regional, Thailand)

   The integrated animal husbandry-cum-fish culture system is Chinese in origin and is widely practised in China. It is also observed in Malaysia, Thailand and the Philippines. Its advantages are obvious; e.g. recycling of farm wastes for dual purposes of waste disposal and protein production on one hand and provision of pond water for agriculture and animal husbandry, on the other.

   In China, farm wastes are used to fertilize the ponds and bottom humus is removed as fertilizers for crop. Grass and vegetables are also utilized as feeds for the major Chinese carps, chicken and pigs, whereas water from ponds is sometimes pumped for irrigation. Thirty to fifty pigs appear to provide sufficient manure to fertilize ponds of 1 hectare in area.

   In the Philippines, fish culture is practised in the floodplain. Fish harvest is possible when the flood water recedes. Subsequently, fruit and vegetable crops are planted. Production of fish is increased by moderate fish stocking.

   In Thailand, the same plot of land is utilized for fish and crop production in alternate years. The portion of elevated land is used for crop production when the flood water recedes.

   The merits of this integrated animal husbandry-cum-fish culture require recognition and support at government levels in order to facilitiate further improvement. Studies are also essential to devise an overall balanced development of both animal husbandry and fish culture.

Summary and Recommendations

Summary

It was recognized that improved design and construction materials are needed in fishpens and cages. Serious constraints are placed on ricefield production of fish due to cultural practices of rice and the present use of pesticides which are harmful to fish. Furthermore, pesticide residues concentrated in fish may be hazardous to humans. There is therefore a need for pesticide use compatible with fish culture.

One way to mitigate the problems raised by increasing population and to maximize the productivity of fish culture systems is to integrate fish culture with vegetable crop and animal husbandry production. Vegetable wastes can be used in fish production, while humus accumulated on fishpond bottom can be placed on vegetable fields as fertilizer thus resulting in an overall production increase with inputs lessened if each is produced alone.

The discussions of freshwater aquaculture designs showed a very wide diversity of development in the different countries in the region. There is a good opportunity for effective technical exchange between countries.

Recommendations

Better and more standardized information is needed on pesticides relative to fish culture.

Better information is needed on all aspects of integrating animal husbandry-cum-fish culture projects. More intensive and widespread practices should be implemented.

With respect to freshwater aquaculture systems the various designs in different countries should be thoroughly surveyed and plans for areas of technical improvement should be implemented especially through the guidance and assistance of regional agencies.

References

Contributed Papers (CPs) 4, 7, 8, 9, 11, 12, 14, 15, 17, 20, 22, 24, 25, 26, 32 and 34
Background Papers (BPs) 2, 5, 7, 9, 10, 11, 13, 16 and 18

SESSION 5
ENGINEERING DESIGNS FOR BRACKISHWATER AND MARINE AQUACULTURE PROJECTS

Overview - M.N. Delmendo (FAO-Regional, Thailand)

The planning, designing and construction of aquaculture projects depend on the farming systems to be carried out and the type of fishfarm to be developed.

Based on physiographic classification, fishfarming may be carried out in three areas, namely coastal, inland and marine areas.

Recent advances in the technology of aquaculture have made significant improvements in aquaculture practices which have resulted in the development of new techniques, particularly in aquaculture in natural waters.

No longer is the practice of aquaculture limited to ponds. Tanks, cages and enclosures or pens used in natural inland bodies of water and shallow marine coves are new aquaculture systems that have expanded aquaculture production. These developments have traditional backgrounds. The present improved technologies are clear indications of the blending of biology skills, engineering know-how and practical skills which make the various environments favourable for fishfarming activities.

Aquaculture, like agriculture, utilizes land and water as a common base of production. It is, therefore, imperative that in planning and designing of aquaculture projects a multi-disciplinary team of experts be utilized in order that optimum use of available resources may be effected. Ideally, such a team would be composed of an aquaculturist, an engineer and a farm management economist. This combination of expertise would bring about a clear picture of an aquaculture project that would give a fishfarmer better production opportunities.

There are various problems encountered in aquaculture development, and one of these is the design of aquaculture facilities appropriate for various aquaculture techniques in different systems.

In brackishwater fishfarming, for instance, an improperly designed and constructed fishfarm project leads to failures in expected output. The management and operation of an improperly design fishfarm often becomes excessively costly and even uneconomical.

In marine fishfarming, the designs that are adopted depend on the experience of the fishfarmer. There are many more engineering problems to be dealt with in natural water aquaculture systems than in land based, fresh and tidal fishfarming systems. On the other hand, aquaculture in natural waters show more applicability to small scale operations than enclosed fishfarming systems.

This Session highlights the relevant aspects of design of aquaculture facilities and attempts to make some suggestions/recommendations in regard to designs appropriate for small scale aquaculture operations of brackish and marine systems; the economic size or unit of aquaculture operation; etc.

This Session also introduced the funding consideration in aquaculture development.

1. Recent Innovations in Design of Brackishwater Pond Projects - C. de los Santos (WVFFPI-Philippines)

   The traditional practice of brackishwater aquaculture is based on the principle of enclosing or impounding tidal water so that fish, either trapped or stocked in the area can be reared for a certain period of time. The most important consideration is to be able to control water inside the impounded area at different tidal fluctuations.

   Several innovations in designs of brackishwater ponds came about as a result of experience of fishfarmers and the influence of improved management techniques that have been developed in recent years. Such improved designs revolve on the principle of efficiency in water manipulations in the fishpond system. Several designs were illustrated and discussed which brought out the advantages over the traditional design of ponds. Economic considerations and efficiency of management were pointed out in the various designs.

2. Nursery Designs in Brackishwater Aquaculture - E.S. Martinez (Philippines)

   The role of nursery ponds was described and some criterion for site selection of brackishwater ponds were presented. The ideal location of nursery ponds should ideally be high, free from trees and acid soils. The location of nursery ponds in the system must be in locations where good water supply and drainage can be attained.

   The size of nursery ponds can be determined two ways and the formula to compute these sizes were presented. A nursery pond design that would facilitate efficiency of operation was also presented.

3. Practical Aspects of Brackishwater Pond Construction - L. Denila (WVFFPI-Philippines)

   Highlights of practical aspects of brackishwater pond construction by manual method were illustrated, emphasizing the possible pitfalls likely to be encountered in the process. A comparative analysis of the traditional method of dike construction and improved techniques were discussed in regard to economy, efficiency and volume of output of labour involved. The advantages of mechanized fishpond construction were found limited and expensive. On the other hand, manual labour with proper direction and supervision, can be more efficient and less costly.

   It was strongly suggested that an improved manual method should be used for constructing fishponds in the region. There is still room for improvements in the present techniques and it is felt that fishfarmers will continue to seek more and more practical ways of fishpond construction.

4. The Design of Marine Fish Cages and Enclosures Used in Aquaculture - W.L. Chan (Hong Kong)

   Attention of the group was drawn to BP-8 for general consideration on this topic. Existing cases are found in CP 2, 9, 20 and 33 for Hong Kong, Indonesia, Thailand and Malaysia situations, respectively.

   It was considered that it would be difficult to arrive at specific designs of these fish culture facilities since they are totally dependent upon the environmental features of selected sites. In particular, current and tidal water transport, topography of the seabed and availability and relative cost of local materials, are relevant. Further, the species to be cultured and the feasible level of input in relation to the socio-economic and in fact infrastructure of such culture systems, must also be taken into consideration.

   Marine fish culture in cages or in other forms of impounding structures is at least 20 times more productive than other landbased pond culture systems, invariably involving premium-value species. This is expected to attract either commercial investments or high national priority in fishery development. In view of these and the fact that the existing design and/or material facilities leave much to be desired, there is an urgent need for engineering back-up support in enabling realistic development of these systems of culture.

5. Designs in the Intensive Culture of Various Marine Organisms - F.O. Ng (Malaysia)

   Some views on designs in the intensive culture of oysters in Malaysia were given and the oyster culture technique in Sabah was used as an example. In Sabah, there are about 40 hectares of oyster farms which mostly use racks to cultivate the oysters. Normally, concrete blocks are used as supporting devices for oyster racks. However, this method still has problems and more studies on oyster rack designs and materials are needed. Rearing trays are also being used which are made of galvanized wire mesh coated with coal tar oil.

   Asbestos sheets are used as spat collectors. A collecting box holding the asbestos sheets is designed to prevent fouling organisms.

   The major constraint in designing of oyster farms in Malaysia is presently the high cost of construction materials making it costly for small-scale operators.

6. Engineering Orientation on Funding Assistance in Aquaculture Development - J.R. Lopez (Philippines)

   At present there are many agencies, both at domestic and international levels interested in providing loans to assist aquaculturists in developing their farms and improving their aquabusiness. However, to convince the banker, the farmers or the aquaculturists need to submit a project with many details concerning the output and input of the farm. The Development Bank of the Philippines requires that aquaculture projects be carefully designed and constructed to ensure the efficiency of production, thereby enabling the fishfarmer to repay his loan.

7. Integrated Agri-Aquaculture Development - E.V. Jamandre (WVFFPI-Philippines)

   Aquaculture needs fertilizers to increase its production. However, the present situation is that the organic fertilizer supply is becoming more expensive and difficult to obtain in the Philippines. To solve this problem, animal production is undertaken. The integration of pig raising with fishfarming solves the problem of supply of organic fertilizer. Pond layout, design and construction of such a system was given. The major constraints based on experience follow.

   1. The high cost of transport of farm inputs make operations costly. This particular farm is located out of Iloilo City. The costs of transportation for construction materials and farm products from the farm to the city are high.

   2. Animal feeds used for terrestial animals need high protein content, but at the same time should be cheap enough for economical production.

   3. The number of pigs should be just enough to produce the required organic manure for the fishponds, so as not to incur unnecessary expenditures in maintenance and operation of the farm.

Summary and Recommendations

Summary

It was clear from the deliberation and discussions which took place in this Session that design and construction of aquaculture facilities are important. The key factors in brackishwater fishfarm operations are the efficiency of water management concommitant with the fish rearing requirements under this aquaculture system.

Innovations from the traditional design of brackishwater fishponds have been evolved through experience of fishfarmers. It was felt that an evaluation of the efficiency of the various existing designs being adopted and a comparative analysis in terms of cost of construction and production performance should be made. This would be helpful in planning and development of aquaculture projects, particularly in small scale aquaculture operations.

Design and construction of aquaculture facilities in marine waters vary depending on local conditions and convenience of the fishfarmer. More investigations are needed to solve the problem of material to be used and prevention of fouling. There is also an urgent need for more engineering back-up support to develop realistic, economical designs and durable materials for use in marine and open water aquaculture systems. The species to be cultured and the level of inputs required should be taken into account in designing the facilities for marine aquaculture.

Recommendation

Standard designs of aquaculture facilities should be made available which could be adopted in different countries of the SCSP region.

References

Contributed Papers (CPs) 2, 5, 10, 13, 14, 16, 18, 19, 21, 23, 27, 28, 29, 30, 31, 33 and 35

Background Papers (BPs) 1, 4, 6, 8, 12, 14, 15, 17, 18, 19, 20, 21, 22, 24, 26, 27 and 28

SESSION 6
THE DESIGN OF HATCHERIES

Overview - H.L. Cook (FAO/UNDP-Philippines)

One of the main problems in aquaculture is lack of fish seeds to stock various culture impoundments. Although there are existing fish hatcheries in the region, the technology for seawater hatcheries is not as advanced as that for freshwater fish hatcheries. Brackishwater aqua-farms still rely mostly on wild stock for their cultured stock requirement. For the benefit of small scale aqua-farmers, the need for hatcheries to bring down the price of hatchery raised fry to a more reasonable price is urgently felt.

1. Considerations in Hatchery Design for Penaeid Shrimp - B. Tiensongrusmee (Thailand)

   In general, shrimp hatcheries require two or three basic considerations for tanks. Breeding tanks should be circular in shape, and width should be given more emphasis than height. They should have a flat bottom declining in one direction. Rearing tanks should be circular, deeper in depth and not be as wide as breeding tanks. Broodstock holding tanks should be circular and provided with a good water filtering system. An adequate and good water supply system, air pump, and aeration devices should also be provided. In designing shrimp hatcheries, the design should consider: economic feasibility of construction; practicality of operation; ease of maintenance; and the satisfying of engineering requirements.

2. Considerations in the Design of Hatchery for the Freshwater Prawn - S. Singholka (Thailand)

   The panelist used a Macrobrachium Research Station in Thailand as an example of how to plan a hatchery. The first factors which must be considered are the planned objectives of the station. In this case the objectives were training of farmers, experimentation and production of juvenile prawns for distribution to farmers. General considerations which will affect the long-term success of a project are:

   1. the visitor area must be separated from working areas;

   2. in isolated areas, a station should have adequate living quarters, and beautification of the grounds should be done to keep the staff satisfied.

   When planning the culture system the numbers and sizes of the different culture units must be coordinated to allow maximum utilization to accomplish the objectives. Separate systems should be provided for delivering air, freshwater, seawater, potable freshwater and green water to points where needed. To ensure an adequate supply of water at all times, a storage reservoir may be needed.

3. The Design of Hatcheries for Saltwater Fish - A.W. Sin (Hong Kong)

   Design principles of fish hatcheries, whether for freshwater or saltwater, are practically the same. In these designs, the biological requirement of the animals to be used in the hatchery should be considered. The materials used in the construction of tanks are concrete, asbestos and fiberglass, but one should utilize as much as possible, materials that are locally available. The problem of erratic pressure in the water supply be solved by constructing head tanks. Aerating devices should be placed in the head tanks so the water is well aerated when it reaches the hatchery tanks. To maintain the temperature of water, some form of sheltering system is needed and in Hong Kong, a heating device is used. The forms of tanks used are either rectangular or circular.

4. Macrobrachium Hatchery in Malaysia - F.O. Ng (Malaysia)

   There was no need for site selection, as the Glugor hatchery is located in the compound of Fisheries Research Institute and is easily accessible. However, for other hatcheries there is a need to select areas where good quality seawater and freshwater are readily available. Availability of electrical power is also a consideration in site selection. At Glugor, seawater is pumped and stored in two reservoirs with water capacities of 400 tons. To prevent plankton growth, opaque roofs are put over the water reservoirs and Tilapia are stocked in them. An air blower is used to supply a uniform flow of air to aerate the water.

   Two types of tanks are in use for rearing larvae: fiberglass tanks of approximately 3 m (10 ft) × 1.3 m (4 ft) × 0.6 m (2 ft) with an approximate capacity of 2 tons and concrete tanks of 16 tons capacity. Concrete tanks are coated with epoxy paint or polyester resin. Small fiberglass tanks of approximately 1 m (3 ft) × 0.6 m (2 ft) × 0.6 m (2 ft) are used for holding and incubation of berried females. Rearing tanks and facilities are located in an enclosed building to protect against excessive heating by solar energy, heavy rain, and infestation by insects, pests and predators.

   The operational problems encountered are: lack of gravid females, insufficient supply of brine shrimp and lack of skilled personnel. A cladoceran which is being cultured in brackishwater tanks is being tested as a possible food substitute in place of brine shrimp.

5. The Design of Hatcheries for Freshwater Fish - P.E. Osborn (FAO/UNDP-Philippines)

   Construction of a fish hatchery itself is not too costly, but maintaining a stock of selected broodstock may be too expensive for small fishfarmers. The hatchery water supply is very important. It should be adequate, properly filtered, shaded and free of fish pathogens and suspended solids. If at all possible, natural waters supplied by gravity flow should be used. Tanks and troughs can be built from many materials as long as they are not toxic. Galvanized iron should not be used and brass fittings should be avoided.

   Aside from the physical and biological requirements in the designing of hatcheries, the following should be considered:

   1. the design should be flexible to allow for future changes, such as changing the species cultured;

   2. spares or back-ups should be provided for all essential equipment;

   3. warning devices should be installed to warn when water level falls and other critical situations develop.

Summary and Recommendations

The Workshop participants recognized that most of the hatchery systems being developed in the region require more engineering input to increase their output and reliability. Especially important are:

1. design of water supply systems including water treatment;

2. specification of materials suitable for construction with emphasis on locally available materials;

3. design of tanks and accessory equipment.

The need was also recognized for biologists to provide data on the biological requirements of the organism being cultured so that engineers can design appropriate systems.

References

Contributed Papers (CPs) 1, 11, 12, 13, 21, 22 and 23
Background Papers (BPs) 10, 19 and 28

SESSION 7
SPECIAL TOPICS IN AQUACULTURE ENGINEERING

Overview - P. Edwards (AIT, Thailand)

An appeal was made for the development of appropriate technology suitable for peasant aquaculture. Small-scale operators include private businessmen, who have limited available capital and are at one end of the spectrum, and peasant fishermen who may only be slightly removed from subsistence level fishing at the other end. Since the latter probably represent a large percentage of the people involved in aquaculture in most countries, they are the ones most in need of technological assistance.

1. Hydraulics and its Practical Application in Aquaculture Projects - R.G. Hechanova (FAO/UNDP-Philippines)

   Flow in open channels was presented as an example of the numerous applications of hydraulics in aquaculture projects. Background of the theoretical analysis of a few situations with uniform flow was discussed. An attempt was made to simplify the use of formulae by presenting appropriate tables and graphs for certain field situations. It was pointed out that uniform flow does not occur in brackishwater fishfarms, and that where there is tidal motion, flow should be treated as being unsteady.

2. Equipment for Construction of Aquaculture Projects - M.M. Lijauco (SEAFDEC-Philippines)

   Categorization of equipment used in the construction of aquaculture projects was presented as follows:

   1. traditional versus modern equipment - modern in the sense that they are labour saving devices;

   2. manual versus mechanical equipment;

   3. equipment used in the pre-development stage or in the development stage.

   The decision as to what equipment is most suitable will depend to a large extent on local conditions. Economics will play a major role but a decision has to be made whether or not to use machinery which will require a low labour input.

3. Pumps in Aquaculture - T.J. Jamandre, Jr. (WVFFPI-Philippines)

   The various types of pumps for brackishwater aquaculture were discussed.

   The writer believes that the axial flow pump is the most efficient, considering the flow heads existing in aquaculture operations. Because of the high cost of fuel, it is necessary to look closely into pump operations. Pumps have to be able to dewater the ponds in a short-length of time in order to harvest before the next flood tide; non-pump equipped pond operators may not be able to do so.

   Brackishwater pumps should be resistant to saline water to ensure long pump life. Manufacturers provide specifications and performance curves which should be consulted before a choice of pump is made. A qualified technician should be hired to study the cost of the pump, its installation and operation.

4. A Survey of Pond Aeration Devices - P.E. Osborn (FAO/UNDPPhilippines)

   The need for appropriate technology to suit the different conditions in different countries was stressed.

   Aeration devices deal not only with dissolved oxygen but also with the other dissolved gases. Molecular motion of water alone is not enough to diffuse the gases. In the United States the blowers and plastic tubings have been found to be most efficient type of aeration devices. In Israel it was known through measurements of oxygen saturation made at sunrise that installation that move pond water by pumping lower layers and spraying them over the pond are more efficient than those which inject air into water.

   A careful comparison of the various types of aerators available should be made from an economic standpoint.

5. Wind and Wave Breaks for Aquaculture Projects - O. Hashim (Malaysia)

   The design of dikes exposed to strong winds and waves was discussed. The most natural and effective form of coastal break water is probably a belt of mangrove trees-100 meters from the coastline. In places where mangroves are scarce or where ponds are not located in mangrove areas, coastal protective structures should be erected. Old tires tied together may be dumped into the water and stacked into the form of a pyramid. This also provides an artificial habitat for fish.

   A design wave should be used in the analysis of coastal dike designs. The shape, height and configuration of the seaside slope must be considered in the design to prevent overtopping and erosion of the slopes of the dike.

Summary and Recommendations

Summary

It was suggested that intensification of aquaculture is necessary because of shrinking land resources available for aquaculture due to rapid population growth. An increase in engineering input will be necessary to increase the fish yield per unit area. Any engineering device employed must be economical, but a choice has to be made between traditional labour intensive methods and more modern capital and energy intensive systems. The choice made will depend on the local situations, but it was felt that the former should be developed where possible to utilize the human resources available.

With respect to hydraulic design, the following suggestions were made:

1. A simplified handbook or manual for the use of aquaculturists should be prepared;

2. There should be a listing of minimum design requirements and component facilities including specifications applicable to small-scale aquaculture projects;

3. There is a need to critically evaluate different design schemes in terms of efficiency, functionality, and other applicable parameters.

Recommendations

1. Standardized practices and methodologies should be prepared with respect to application of hydraulic engineering to aquaculture projects, including consideration of kinds and types of pumps.

2. More consideration of aerators is needed to improve fish production and to determine the best kind of aerator.

3. Continuing review of machine and manual construction capabilities and costs are necessary to obtain good construction, at lowest costs, of aquaculture projects.

References

Contributed Papers (CPs) 1, 12, 14, 16 and 21
Background Papers (BPs) 1, 8, 10, 12, 13, 15, 17 and 24

SECTORAL MEETING A - AGRI-AQUACULTURE ENTERPRISES

Present

This particular session was held in a piggery-fishfarm project owned by Mr. E.V. Jamandre of Iloilo City, which was visited by the Workshop.

An ocular inspection of the pig/fishfarming project was undertaken by the participants after which discussions were held at the site.

Integrated farming activities have been widely practised in Southeast Asia particularly in China. There is no doubt that this system is highly feasible and facilitates the use of organic waste resources in the production of food crops of direct use of human beings.

However, there are biological problems as well as health hazards associated with the use of organic manure in fishponds. These are:

1. excessive amounts of animal manure lead to fish kills and hence, losses to the fishfarmers

2. the taste of fish raised in heavily manured ponds sometimes is unacceptable and may have an off-flavour.

The quantity of organic manure produced by animals are known. However, the amount of manure required to produce a quantity of fish per unit area is not yet established. The level of manuring which will yield maximum production and will not result in fish kills should be determined so that fishfarmers can be forewarned.

Recommendations

In this connection, it was noted by the Workshop participants that follow-up studies are needed to determine the quantity of organic manure needed to produce a given quantity of fish so that either an excess or a deficiency of manure can be avoided. This would also reduce the cost of inputs for feeds of animals in relation to the fishfarm requirement.

The economics of small-scale integrated farming systems should be determined to serve as basis of policy formulation.

SECTORAL MEETING B - PEN AND CAGE CULTURE

30 November 1977

1. Introduction

The level of success and therefore, the future commercial feasibility of impoundment fish culture systems in natural water bodies are to a great extent dependent upon the design and facility of materials used. Based on the experiences discussed in the Workshop, this consideration is stressed by reference to the potential adverse effects on impounding facility inputs, of weather and other aquatic environment characteristics inherent in countries where these systems have recently been commercially introduced. Since these introductions were primarily at the initiative of the operators and therefore in the absence of appropriate control, urgent improvement of the present deficiencies in these systems of culture is considered necessary.

The problem areas are concerned with the design and choice of materials currently used in pen and floating cage fish culture in the Philippines, Hong Kong and Malaysia, respectively, in which engineering back-up is essential to minimize the potential loss of input on one hand and to maximize the assurance of an economical level of output on the other.

2. Present Status

Pen culture

The present fish culture pens in Laguna de Bay lake, Philippines are characterized by having high, fixed structures above the water level. These are subject to the adverse effects of typhoons and other adverse weather conditions, and coupled with the frequent threats of mass drift of water hyacinth, damages to the impounding structure and therefore, loss of fish stock are the undesirable features of this system of culture. The only course of action in rectifying these deficiencies is to improve present technology by systems that can overcome these problems.

Floating cage culture

In Hong Kong, the diverse variety of materials used in this system of culture clearly indicates the need for further development, especially in regard to the frame of the raft and the floatation devices used. Similar to the Laguna de Bay situation, and being in the typhoon area, Hong Kong also stressed the need for engineering back-up in improving the material strength and design of floating rafts.

Although still in the trial phase, floating cage culture in the west coast of Peninsular Malaysia has experienced high rates of fouling on netting (polyethylene, knotted) materials. Since this phenomenon causes serious culture management problems, it is a priority area necessitating immediate solution.

3. Recommendations

The sectoral group therefore, recommends:

1. the trial of a floating net pen of about 0.5 hectare size with the view of ascertaining the merit of this method of impoundment;

2. the trial of other forms of floating raft devices in Hong Kong;

3. full engineering back-up in the design and material development of facilities in these undertakings; and

4. the assistance of structural engineers, coupled with biological research back-up, in resolving the acute problem of high rates of fouling that have been experienced.

SECTORAL MEETING C - SMALL-SCALE SHRIMP HATCHERIES

1. Introduction

Small-scale shrimp hatchery has received more interest and now plays a significant role in supplying of shrimp fry to aquaculture industry. However, the need of engineering back-up in the design of equipment and facilities such as aerators, pumps, waterflow system and tanks is required for efficient hatchery management.

2. State of the Art

The air-lift pump for improving the quality of water was discussed by H.L. Cook. Panel type air-lift pumps are made of readily available materials to direct the water in the desired direction and provide water movement sufficient to scour the bottom and keep particles and detritus suspended in the water. Air can be distributed through air stones or perforated pipes located near the base of the air-lift. The size of air bubble in this case will play an important role in efficiency of the device. The foam at the top due to layering of bubbles may cause problems. However, this can easily be solved by periodic skimming.

S. Singholka touched on problems in Macrobrachium hatchery which is done as a small-scale industry by fishfarmers in Thailand. Seawater used for hatchery operation is very vital. The low salinity can be brought up to higher salinity level by adding salt. However, it is not satisfactory to dissolve crystal salts with freshwater to be used as rearing medium for Macrobrachium fry. The question about the need to build a hatchery near the sea was discussed. It seems more economical for the small-scale prawn farmer to bring salt water from the sea to the hatchery sites, than to locate the hatchery near the sea. However, one needs to transport broodstocks from the farm to the hatchery and the fry from the hatchery to the farm. There is evidence that the cost of transporting seawater for hatchery operation is small and is negligible in comparison with the cost of freshwater that needs to be used daily and which is difficult to obtain when the hatchery is located near the sea.

T.J. Jamandre, Jr. gave some highlights on the need of engineering back-up in the design of hatchery facilities. He recommended that spare equipment should be provided for back-up support, especially power generators to avoid failures of operation in case of power cut-off or shortage. Lack of extra back-up equipment under this situation can result in high mortality of larvae in the hatchery.

3. Recommendations

It is necessary to evaluate the efficiency of the facilities that are presently used in small-scale hatcheries with the view of improving efficiency of such hatcheries. The government of concerned countries should initiate the required programme in support of small-scale aquaculture development. In this regard assistance of regional and other suitable agencies and institutions should be sought.

SECTORAL MEETING D - BREAKWATERS FOR AQUACULTURE PROJECTS

Present

1. Introduction

Breakwaters are being used to protect aquaculture projects against wave action, especially the outer coastal dikes in some countries of the world. The size and types usually vary depending on the conditions for which they are constructed. Because of the recognized importance of these structures, it is imperative to assess applicability and need for breakwaters in the Southeast Asian countries. The discussion of the topic covered not only coastal breakwaters but also small wave protection of dikes within pond units.

2. State of the Art

Coastal breakwaters are widely used in aquaculture projects that are exposed to the sea, such as those in Japan and Taiwan, China. The Philippines and Thailand are already beginning to experience coastal erosion because of denudation of mangrove for a number of purposes and their conversion into fishponds, if not properly designed. This problem however is minimal in parts of Thailand and in Indonesia because brackishwater fishpond projects are still located inland and in protected areas.

Examples of coastal breakwater or protection follow:

1. Permanent or semi-permanent types such as concrete, combinations of concrete forms and large pieces of rocks and floating types.

2. A wooden type formed by driving two lines of selected mangrove piles in front of the dike at some distance. The space between the lines is filled with branches of trees. The ends of the piles are tied up together to increase strength. Aside from dampering wave energy, the branches of trees drop mangrove seeds that grow in the area. The row of branches also cause sediment deposition leading to soil accretion. This type is claimed to be effective in the Philippines.

3. In Malaysia, worn-out tires are tied together in pyramids and arranged to form an elevated barrier. An advantage of this barrier is its use as a reef to attract fish for spawning and congregating in the area.

4. A natural buffer zone of mangrove trees. In the Philippines and Indonesia, buffer zones are 100 and 400 m wide, respectively.

There was a general consensus that dikes should be protected against internal waves (waves inside ponds). Examples of techniques presented are given below:

1. Proper orientation of the pond with respect to the direction of the prevailing wind. The idea is to minimize the “fetch” or length of exposed area to wind thus minimizing the height of wave.

2. Positioning dikes normal to the direction of wave to obtain good wave reflection (resulting in a standing wave) that in itself dampens the wave energy.

3. Reduce the “fetch” by constructing permanent or temporary barriers carefully placed in position. Such barriers consist of small and short dikes constructed at intervals across the direction of wind/wave, and lined twigs or branches of trees which also intercept drifting fish food.

4. Driving bamboo poles vertically side by side along the sides of dikes. A combination of this with branches of trees is also being done.

5. Floating bamboo rafts (tied in 3's) anchored ahead of the dike.

6. Worn-out tires arranged side by side along the slope of dike.

7. Straw mats on dikes.

8. Riprapping of dike with either concrete or rocks.

9. Growing of creeping or close-growing grasses on dikes.

10. Carefully designed jetties or wave deflectors and gabions along dikes.

11. Planting of appropriate trees along perimeter dikes to reduce wind energy.

It appears that there are indigenous techniques and construction materials available in the region that are worth looking into. Those effective under a given condition could be singled out for adoption in aquaculture projects.

J. Katoh presented a theoretical analysis showing wave factors on breakwaters for different wave characteristics and bottom slopes.

3. Recommendations

It is necessary to evaluate the effectivity of the enumerated types as to their feasibility, their relative effect in dampening known wave energy, durability and life.

The needs for structural protection should be viewed from a total approach.

The government of concerned countries should initiate a move to identify the areas where breakwaters are needed and to draw construction plans and action for implementation. In the Philippines it was proposed that the Government should consider providing large-scale breakwaters for coastal areas as infrastructure, on a cost-sharing basis. This would be much more effective than separate piece-meal work by individual pond owners.