THA/75/012/WP 3
MANAGEMENT IN CLARIAS CULTURE, THAILAND
|
THA/75/012/WP 3 MANAGEMENT IN CLARIAS CULTURE, THAILAND |
by
James Muir
Institute of Aquaculture, University of Stirling
Scotland
Consultant to
the
Programme for the Development of Pond Management Techniques
and Disease Control (DoF - UNDP/FAO THA/75/012)
Thailand
National Inland Fisheries Institute
Bangkok, Thailand
1981
The “Programme for the Development of Pond Management Techniques and Disease Control (THA/75/012)” was implemented in Thailand during 1979–82 as a joint project by the Department of Fisheries (DOF) and UNDP/ FAO. The purpose of the project was to improve DOP support services for Clarias farming through strengthening:
the skills of Fisheries staff in aquaculture disciplines such as disease diagnosis and treatment, pond management and extension,
the research on solutions for problematical aspects of Clarias culture,
the system of relaying problems from the farms to DOF and of transferring improved technologies, and
the equipment and facility base of DOF for working on aquaculture problems.
Although the UNDP/FAO participation was structured to terminate in August 1981, DOF committed continuation of the project to at least August 1982.
This report is one of several Working Papers prepared on various aspects of the project. A list of titles of reports completed in the series is annexed.
Inquiries concerning the subject matter of any particular report should be directed to the author,
c/o The Director
National Inland Fisheries Institute
Kasetsart University Campus
Bangkhen, Bangkok 9
Thailand
Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.
This electronic document has been scanned using optical character recognition (OCR) software. FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.
3. PONDS: SIZES AND CONSTRUCTION
7. GROWTH AND PRODUCTION RATES
9. WATER CHEMISTRY IN CLARIAS CULTURE
10. ENVIRONMENTAL CONTROL MEASURES
11. PRESENT FOCUS OF DEVELOPMENTS
2. Typical water supply systems in Clarias ponds
3. Occurrence of principal events relating to typical double-cropping Clarias culture
4. Aerobic system in Clarias ponds
5. Anaerobic system in Clarias ponds
6. Feeding rate and growth curve in a representative Clarias culture operation
7. Approximate mass-balances in a Clarias pond
9. Example layouts of systems for cleaning-up discharge water for re-use in rearing ponds
11. Scheme for long-term research trials on effects of water chemistry characteristics
1. Basic economic parameters of Clarias farms in Suphanburi and Nakon Nayok provinces, Thailand
2. Example tolerance levels of water chemistry characteristics in fish
MANAGEMENT IN CLARIAS CULTURE, THAILAND
James Muir*
The Institute of Aquaculture, University of Stirling, was retained as consultants on disease control and pond management aspects of the DoF - UNDP/FAO project (THA/75/012) for assisting Clarias farming in Thailand. Stirling's input was guided by the following terms of reference:
Review the design and management practices of typical Clarias farms in Thailand, identify problematical aspects and recommend corrective measures.
Investigate the performance of water chemistry parameters in Clarias culture systems and provide a qualified opinion:
On tolerance limits of a given parameter for air breathing species such as Clarias.
Accounting for undue levels of a parameter
On ways to manage acceptable levels of water chemistry in a Clarias pond.
Recommend researches to investigate or test methods for improving Clarias culture.
Provide bio-engineering and management guidelines that will contribute to the control of diseases and excessive mortalities in Clarias culture, and provide the rational for recommended measures.
Contribute to the preparation of a “disease handbook” for Clarias culture in Thailand through including aspects that relate water management, pond design, etc. to disease control.
The team assembled by Stirling to confront the assignment comprised fish pathologists, aquaculture biologists, bio-engineers and experts in pathological techniques. Following a preview mission to Thailand in March 1980 by the coordinator of the Stirling team, the disease contingent studied relevant aspects of the assignment in Thailand during May to August 1980. Bio-engineering and management aspects were field studied by a further mission to Thailand in September and October 1980. This report presents the results of the latter mission which drew its basic information from site observations, findings of preceding team members, pre-existing Thai reports and summaries as prepared by Fedoruk (1979) and Varikul (1980).
Clarias farming has grown substantially in Thailand over the past 20 years. The present number of farms may be in the order of 1,000; they vary from operations with one pond to complexes of 30 or more ponds. The technology is primarily artisanal and in essence is an intensive pond culture system structured on large inputs of trash fish as the principal food.
Early farms which set the basic technological pattern concentrated in areas within a 150 km of Bangkok, a primary market center and a major channel for the supply of trash fish. As the system bacame more practical and known Clarias farming started in other parts of Thailand. Small concentrations of farms now occur in the south drawing trash fish supplies from local sources and in the north and northeast where food supplies may chiefly consist of animal and freshwater fish wastes.
As Clarias farming emerged so did problems which manifest to threaten the viability of the culture system. The price of trash fish, a very sensitive component in the economic structure of Clarias culture, is increasing inordinately with respect to the farm gate price for Clarias. Furthermore, the trash fish is frequently of poor quality and sometimes incapable of providing the expected nutrition. The quality of replenishment water is often unsatisfactory and supplies are so limited in the majority of cases that ponds cannot be adequately flushed particularly when fish are in distress. Disease is rampant at times and is apparently due to the singular and combined factors of nutritional defficiencies, toxic water chemistry conditions and pathogenic infestations. Mortality through a grow-out production cycle is relatively high being usually in the order of 70 to 80%. Although the incidences and degree of mortality varies from operation to operation, and sometimes between ponds within a farm, a temporal pattern of relatively large losses commonly recurs: a initial stocking mortality happens in most cases followed in 40 to 60 days by another incidence of mortality; a final period of marked mortality occurs in the final stages (90 to 120 days after stocking) of a grow-out cycle.
In spite of these problems Clarias farming persists. Its continuation and expansion is inspired by some operations which can repeatedly produce enough fish to evidently gain suitable profits. Overall, Clarias stocked at rates ranging from 60 to 300/m2 can be farmed to marketable sizes of 120 to 200 grams in 3.5 to 5 months. Yields in a production cycle can range from 3 to 12 kg/m2 of pond area depending upon the incidence of mortality.
Clarias rearing has differnetiated into three sectors: (i) fry production - which breeds adults in large ponds and collect fry for sale, (ii) fingerling production - which purchases fry and rears them until about 5 to 7 cm in length, and (iii) grow-out production - which purchases fingerlings and rears them to market size. The fry and fingerling operations are mainly in Chacheongsao Province about 150 km from Bangkok. Grow-out operations occur in various parts of Thailand and seemingly employ similar basic practices.
Two species of clariids (C. batrachus and C. macrocephalus) are farmed. Almost all the production, however, is due to C. batrachus. The following account relates mainly to grow-out operations of C. batrachus.
Ponds range from 300 to 2,000 m2 in area, and from 1 m to 1.5 m in depth but larger and deeper ones occur. Available soils usually retain water adequately, so little preparation is required. Excavated materials are commonly used to form the embankments around the pond, and as bottom soil is cleared periodically, it is added to the embankment.
Water service arrangements are relatively simple - water is either introduced and drained by a simple channel and weir, or is pumped in and out by long-tail pumps. (Fig 1). Three basic layouts of water supply systems, as illustrated in Figure 2, are noted to occur. In favoured areas with adjacent irrigation canals, water supplies may be drawn in parallel from the main source which does not receive discharge from other Clarias farms. In other areas water is drawn from and discharged into klongs thus receiving and contributing Clarias wastes to a common source. It was not possible to assess the relative numbers of farms possessing different layouts, though this would be important. Observation of some systems suggested that a change of use (e.g. for vegetable crops) could be relatively simple.
Stocking times are determined by the availability of seed fish which are mostly produced by farms specializing in the production of Clarias fingerlings. Production of seed stocks generally starts in March or April and continues with successive crops through to August or September following.
Most operations grow or attempt to grow two crops, each requiring 4 to 4.5 months of grow-out time, in a cycle. The first crop tends to be more successful than the second for both marketing and pond problem reasons. Peak production of Clarias from capture fisheries, with a consequential reduction in prices, may overlap the harvest time of the second crop which cannot be sold advantageously. Furthermore water supplies tend to be scarce during the latter stages of the second crop thus preventing adequate flushing when problems occur. The timing of principla events that have a bearing on a double cropping Clarias system is illustrated in Figure 3.
Figure 1. Long - tail pump
Figure 2. Typical water supply systems in Clarias ponds
Two major stocking policies appear to have been developed; a highly intensive approach, common in Suphanburi Province and a less intensive method as employed in Nakon Nayok Province. In Suphanburi initial stocking densities are much higher compared with those in Nakon Nayok. The Fisheries Department through NIFI has been attempting to pursuade farmers to stock less intensively since information from experiments generally shows that survival rates are comparatively higher when stocking rates are lower. The farmers attitude, however, is obdurate and it is based on stocking as many as possible in the hope of the largest number possible will be harvested.
Production management as such is rudimentary. Continuous cropping, stock weight control or scquential pond use is not practised. Thus the fish introduced are cropped out in a single harvest at the end of a production period, at a mean weight of 120–150 g which represents a theoretical maximum production per crop of 100 NT/ha. Assessment of fish size or total crop held is not normally done, and the farmer is not usually aware of stock condition throughout the growing season.
Harvest of fish is dictated either by planned marketing, or more frequently, by anticipation of seasonal market price falls, or by neighbouring farmers harvesting, often discharging disturbed and heavily polluted water into the supply water of the operators farm, forcing the harvest. The decision may also be influenced by the availability of transport or the terms of the handling agent, who is often the supplier of fingerlings, food or credit to the farmer. Thus in many cases the time of harvest is not particularly dictated by fish husbandry considerations.
Feeding is normally based on trash fish, transported from port areas, and on locally available rice bran and cooked rice. The normal ongrowing diet is 4:1 trash fish to rice bran, mixed together, cooked and fed as a paste. As a fattening diet, 8:1:1 trash fish, rice bran, rice, is used, though this practice appears to cause deficiency-related symptoms (“crack-head disease”), and frequent mortalities. The practice, however, is maintained since the farmers themselves do not appear to be aware of this link.
Figure 3. Occurrence of principal events relating to typical double-cropping Clarias culture
Food is assumed to be fed in controlled quantities by moulding the paste into hand-sized lumps, fed successively until the fish no longer respond to the food. In practice, if hired labour is used, the there may be little control of the amounts fed, and considerable waste and unnecessary fouling of the water may occur if the fish do not feed. As fouling may further reduce the fishes `feeding response, this may have severe cumulative effects.
Judgement of feeding quantities does not appear to be standardised, though ‘rules of thumb’ exist, in terms of amounts fed during each month of growth. They are apparently based on pond area, and are perhaps influenced by a neighbouring farmer who has already raised Clarias. If this practice is followed, it is clear that at the beginning of each month the fish may be overfed, while towards the end of the month the fish become underfed as they continue to grow.
The control of feeding and the effects of food and faecal wastes are very critical aspects in the maintenance of environmental conditions, and on the production of fish at reasonable costs. Developments in pellet foods are now emerging, as trash fish food costs rise, and as the possibility of reducing adverse environmental effects becomes apparent. There is as yet no study of the relative effects of the different feed types, though this is likely to be important. The use of pellet foods may also be important in the flexibility of storage, and the reduced dependence on trash fish supplers, though the costs for the purchase of food may still be the same.
The Clarias culture system in Thailand is unique with respect to fish culture system in using an anaerobic environment through a major portion of its production cycle. Studies by NIFI show that in the early stages Clarias ponds exhibit conventional patterns of actively photo-synthesising aerobic environments with typical diurnal pH, CO2 and oxygen fluctuations with waste nutrients being taken up in primary production (Fig. 4). The early mortalities observed in Clarias culture may be associated with the rapid fluctuations in water quality characteristics in this highly eutrophic system.
After about 6 to 10 weeks from first stocking the system starts to go anaerobic, presumably due to the shading caused by accumulations of suspended solids. From this point onwards the system appears to remain continuously anaerobic, with at the most a very thin aerobic layer. Although these have not been studied fully, it is expected that conventional anaerobic processes will occur, as evidenced by the release of H2S (Fig. 5). Paradoxically by conventional experience, Clarias has a tolerance for the chemical characteristicss of an anaerobic system, at least in the early stages of the system, suggesting the benefit of greater environmental stability.
Figure 4. Aerobic system in Clariasponds
Figure 5. Anaerobic system in Clarias ponds
As the culture season continues, however, the mortality levels appear to increase, presumably as levels of either NH3, H2S, solids, or some as yet unidentified factor reach the levels of tolerance of the fish, and the anaerobic system reaches the limits of its support. As Fig. 5 shows, the processes involved are unable to remove NH3, H2S, or solids from the environment. It is clear at this stage that a greater understanding of operation of the present conditions is required, particularly in considering the dynamics of biological productivity and nutrient pathways, and the role of bacterial populations.
The exchange of water appears to be parctised on a limited basis only, and it is not clear what quality of water is available to farmers, though it has been stated that external water sources are at times less acceptable than those within the ponds or that the farmer has no certainty of good water supply. Regardless of these questions, it is not certain whether the sudden change of conditions might stress the fish stocks further and have an additional adverse effect.
Figure 6 shows a growth rate curve deriving from studies of a typical Clarias farm by NIFI. it illustrates that the limitations caused by reduced feed levels (as disussed in Section 5) are particularly significant, and that there is practically no growth in the last 4 to 6 weeks of a grow-out cycle. Wether or not this is completely typical of Clarias operations is moot. The illustration, however, is certainly indicative of the problems in husbandry and management that can be experienced.
Production rates, as recorded elsewhere, are remarkable by conventional pond system standards, attaining levels of 100 MT/ha/crop (200 MT/ ha/yr in a double cropping system) compared with an average of 10 to 15 MT/ ha/yr in well managed photosynthesising systems and up to 30 MT/ha/yr in experimental small ponds in Israel (Saring, 1978). This is important in the context of the maximum allowable weights in aerobic systems, if it is desirable to maintain these for Clarias. In comparison with the Israeli system achieving 30 MT/ha/yr, the Clarias system attains 5 to 6 times more production in an aerobic periodic that is no more than 5 or 6 months.
Production rates are comparatively lower in the Nakon Nayok area of Thailand where less intensive stocking is practiced but 3 or even 4 crops are raised in a pond each year. Rates are approximately 40 MT/ha/ crop and in the case of 4 crops the annual production is 160 NT/ha. There are as yet no comparisons between effectiveness of production methods, though on the basis of growth rates (Fig. 6), there could be a considerable improvement.
Figure 6. Feeding rate and growth curve in a representative Clarias culture operation
An assessment of the economics and risks in Clarias culture is essential for considering the reasons for adopting particular culture practices and in determining the means available for improving culture methods. Preliminary results from a detailed study on the economics of Clarias culture made by Kasetsart University's Department of Agricultural Economics became available at the time of this study, to provide some information on economic factors of Clarias farming in Suphanburi and Nakon Nayok provinces as summarized in Table 1.
| Parameter | Suphanburi Farms | Nakon Nayok Farms |
| Typical farm size | ||
rai | 30 | 5 |
ha. | 4.8 | 0.8 |
| Pond size (m2) | 400–1,800 | 400–1,800 |
| Stocking rate (fry/m2) | 177–194 | 44–93 |
| Total food input (kg/m2) | 23 | 7 |
| Production (kg/m2) | 9.6 | 4.0 |
| Food conversion | 5.35 | 4.26 |
| Food as % of operational cost | 33.6 | 50.0 |
| Operational cost | 16 | 14 |
| (฿/kg fish produced) | (15.0–22.5) | (13.0–16.5) |
| Av. farm gate price of fish (฿/kg) | 19.41 | 19.69 |
| Gross profit (฿/kg fish produced) | 2.75 | 5.10 |
| (1.7–4.4) | (3.2–6.7) | |
| Land cost (฿/m2) | 0.66 | 0.47 |
It is apparent firstly that the Clarias culture industry is heterogeneous, with a number of different types of operation identifiable and as such there is a wide variation in culture practice, inputs and returns. As described in earlier studies, the industry is still very cyclical, having a remarkably short lead-in time, and thus farmers can move in and out of the business very quickly with corresponding instability in markets.
Although there have been notable profits made in the industry, particularly amongst the larger farmers (cf. losses for smaller farmers), the average level of profitability is often low, and frequently negative. As a number of farmers leave the industry with accumulated debts, there may well be a negative or zero return on the whole industry, though this is difficult to determine. It appears however that some of the profit made by the larger farmers (who incidentally have been the source of much of the information concerning Clarias culture) is gained at the expense of the smaller farmer, in seed fish, feeds, transport, or credit. In these circumstances the role of development must be considered carefully. Firstly, is the aim of improvement that of increasing production or that of assisting the smaller farmer and in turn local employment? If the latter, the problems of development are more acute, as the present dependence on outside agents for supply of foodstuffs and sale of fish, and on the advice of neighbouring farmers for husbandry and management practice makes it very difficult to establish and effective structure for development. Moreover, the observed instability of the market suggests a rather more limited market size in the prices hoped for by the Clarias farmer, and as trash fish and fry prices impose restraints, the margin available for the farmer must be considered carefully.
During one of the field trips, the difference between ‘successful’ and ‘unsuccessful’ farmers was checked by interviewing a Clarias farmer in the Suphanburi area who had gone out of business in the last few years. As most recorded data concerns successful production, it was extremely enlightening to observe the numerous reasons an otherwise enterprising individual was unable to continue farming profitably. The main points of the interview are presented in the footnote1 below.
Obviously enterprising and innovative. Since ceasing Clarias culture he is using part of the pond space for vegetable production; he is still raising Puntius in cages in one pond. He had tried integrated farming with pigs and carp and tilapia. Pond space could be restored for Clarias use with little alteration.
Was reasonably successful in first two years and expanded to take up most of the land area of the farm. Funded from his own reserves then incurred bank loan.
Felt production was satisfactory but could not estimate actual costs.
Was forced to harvest by mounting food costs and did not get good price; finally lost 2–3 ฿/kg of fish.
Considered markets to be the most important factor in production. Disease and water quality problems were secondary.
Realized the great fluctuations in Clarias market and appreciated the idea of re-entering Clarias farming as others were leaving.
Is keeping watch on price and would certainly consider trying Clarias farming again if price was right although he still has some doubts.
Large farmers control fry and feed supplies, and could usually profit from small farmers even in poor market conditions when their own crops were less profitable.
Thought Government organization and intervention could help but uncertain of practical effectiveness.
Had attempted to organize fish farmers cooperative.
The feasibility of technical or management measures for improving Clarias production, the margin available (if these improvements result in extra costs), or the additional initial costs (even if these are recouped by improved production) and the effects on the farmer's perception of the risk involved are critical considerations. Thus developments like improved foods, better management and marketing procedures, and disease control, which may involve relatively little extra cost, could be more easily introduced, while technical developments such as filtration, aeration, additional pumping etc., may be difficult to introduce, even if longer-term benefits are apparent, as the farmer's attitude will be to produce fish at the least possible cost, particularly capital cost. At the very least the spread of technical development will necessitate clearly improved production figures and demonstration units, together with a clear understanding of how technical developments can be brought in. It is clear that in the ecology of Clarias culture and its management, technical improvements are likely to be obtainable only through a good understanding of the processes involved. Unless this understanding is available to farmer, additional technical inputs may be wasted.
Using some of the figures shown in Table 1, an estimate of the margin available for technical developments can be made. For the larger, more successful farmers, profits can be as much as ฿2.5/kg, or ฿250,000/ crop in a 1 ha area (100t production). It is difficult to ascertain at this stage how many such crops are successful, but if, say 1 in 5 crops were to fail because of disease/poor environment, the loss of profit alone could average ฿100,000/ha/yr, and if all of the production cost was lost in the failed crop, at approx ฿15/kg, the averaged loss (profit + production cost) could reach ฿500,000/ha/yr. Thus any developments with an operating cost (including capital charges) of less than ฿100,000/ha/yr (฿0.5/kg) would be theoretically feasible at this rate of loss.
For the smaller, less successful farmer, however, the position is less clear, as profit margins are generally far less (e.g. ฿0–0.5/kg), and at the higher profit rate, a one-in-five failure allows only ฿0.1/kg for technical imrpvements. However, if the present high costs reflect mortalities or other production inefficiency caused by poor environmental conditions, there may be a greater return available through improved production methods. What is more important at this stage, of course, is the farmer's preparedness to take up these extra costs in advance of obtaining a return from them, and in this context a fully evaluated trial, technically, biologically, economically would be vital.
Another important point to make is that at these comparative levels it is worth more to the larger and more successful farmer to adopt improvements and if the cost are less than say ฿0.3/kg they will produce extra profit; for the smaller farmer, however, such a cost would reduce dprofit, with the result that the technical improvements could theoretically increase the advantage of the larger farmer, and in the longer term drive the smaller operator out of the business.
Obviously the analysis of potential gains, or value of technical improvements requires more detailed analysis than that possible on the basis of currently available information, the relationship must be tested against the longer-term prospects for the industry. However, these figures do suggest the level of development sustainable in present circumstances.
There are a number of important economic factors to be considered further, and it is hoped that a further survey will reveal additional information. Ideally, this should be tied in with a more clear technical description of the systems and production cycles used, in which case a more accurate pricture of the main problems can be obtained.
Additionally, the role of co-operatives or other economic structures could be considered, if the traditional ‘middlema’ problem is to be avoided; in spite of the known problems of co-operatives, it is difficult to see the adoption of improved methods by individual small farmers.
Preliminary results in the aeration trials suggested that levels of unionised ammonia in Clarias culture systems were of the greatest significance in disease and mortality, though in the earlier stages the fluctuating photosynthesising/respiration cycles in the ponds, with associated O2 and pH changes, appeared also to cause stress and mortality. As hydrgen sulphide levels were likely to be problematic, though at the low pH levels normally encountered, H2S will be in the more toxic forms.
The relationship between water quality, bacterial levels, stress and disease appears to be the classical one of combined causative effect, in which none is by itself responsible for disease and mortality.
There is unfortunately little information on the long-term effects of either NH3 or H2S on most species let alone air-breathing species. The role of O2 levels in NH3, H2S and effects on respiratory processes in air-breathing species also require further elaboration.
Some of the recorded tolerance levels for fish are shown in Table 2.
Table 2: Example tolerance levels of water chemistry characteristics in fish
| Characteristic | Tolerance level |
O2 | 0.89 mg/L @ 30°C lethal for Ictalurus; |
| 0.8 mg/L @ 20°C lethal for carp; | |
| 0.6 mg/L lethal for tilapia | |
NH3 | 0.28 LC50 48 hr, NH3-H brain cholinesterase is actively depressed in Clarias batrachus |
CO2 | 40 mg/L limits salmonids; nephrocalcinosis occurs in some fish when CO2 is 10 mg/L |
NO2 | 96 hr LC50 at 24.8 mg/L for Ictalurus |
NO3 | 1400 mg/L lethal for Ictalurus |
| Suspended solids | trout gills are seriously affected by 800 mg/L diatomaceous earth |
H2S | lethal to fathead minnow at 57.2 mg/L (pH 7) and at 14 mg/L (pH 8.7) |
Compared with the known levels in Clarias culture ponds, it is clear that tolerance must be considerably higher. Blood chemistry examination has shown that low O2 levels cause changes in erythrocyte numbers, and produce low haematocrits.
In these respects the experiments currently under way to determine toxicity will be quite critical, and it will be useful to examine the histology and haematology of the test animals to identify the physiological effects. It would also be useful to consider whether NH3 alone is toxic, or whether NH4 + also exerts an effect, as the exchanges and toxic effects may be different in air-breathing conditions. In this case, the effects at low and high O2 levels could be important.
Apart from the short-term effects determined in conventional trials, it would be useful to consider a longer-term trial, in which the relationship between environmental conditions and growth could be determined. The current feeding practices appear to limit growth rates, and there may be long-term potential in decreasing crop time at lower stocking densities. It would be relatively simple to devise a trial to determine these longer-term effects (Fig. 12, and opportunity may be made to examine the combined effects of e.g. NH3, O2, or NH3, O2, H2S.
The outline of the culture system environmental conditions, based on experimental work at NIFI has been given earlier. Although the precise uptakes and transfers by particular components have not yet been determined, the NIFI information allows a preliminary estimate of the “mass-balance” of nutrients passing through the system and their potential for accumulation within the system, as shown in Figure 7. Firstly it is clear that the major cause of the environmental conditions occuring is the metabolic output of the fish possibly together with the breakdown of uneaten food. In the anaerobic pond conditions present, the crucial end-products of N, P, S, C and the major elements in the foods, will be present in reduced forms, e.g. NH3, H2S, CH4. Considerable amounts of oxygen (10–30kg/day) would be required to maintain the system in an aerobic state. While this could be met by photosynthesis, it appears that shading by particulate matter prevents this.
The role of particulate matter and benthic material in the ponds is not yet clear. Eventually, suspended organic material should become oxidised and mineralised, and tend to become more settleable, though the activity of the fish will tend to maintain a continuous suspension. In these circumstances it is difficult to provide suitable conditions for photosynthesis, unless mechanical or biological filtration is employed.
The role of the benthos and suspended bacteria should be examined as part of the experimental work, in case there are causes of significant dynamic instability, or the possibility of improving the biological uptake of waste products (e.g. benthic worms to be consumed by the fish). There is no background on this type of system in the fish-farming literature, in spite of the improving level of understanding of aerobic culture systems, though that of anaerobic lagooning in waste treatment offers the closest parallels, and literature is currently being checked.
Figure 7. Approximate mass-balance in a Clarias pond.
The nature of these relationships will have direct implications on the feasibility of use of aerators, filters, or the increased use of water in the culture systems, and it is thus important to know the overall relationships taking place and their relative stability for management purposes.
There are a number of methods by which water quality can be maintained or improved, though their use would have to be considered carefully for the particular environmental and economic conditions in Clarias culture.
Careful Management Control: The economic and other descriptive surveys being planned should help to indicate whether lower stock rates, possibly with higher feed rates and growth rates would improve risks and overall profitability. At present, apart from initial parasite control, there are few management procedures used, and the most important control is the observation of feeding behaviour and the rule-of-thumb guides to feed rate. As mortalities occur, water is changed, but lack of knowledge of supply quality makes this a difficult decision. Some of the important things to consider are:
The identification of critical water quality factors in the conventional anaerobic system, e.g. can we predict mortalities on a time “x” concentration basis?
An understanding of the capacity of pond systems to support waste output and a knowledge of the amount of food it is possible to feed - this could be particularly useful at early stages in order to improve growth rates.
Knowledge of the stability of pond conditions and the sensitivity of particular production stages.
Better knowledge of water quality conditions, both in the ponds and in supply sources - preferably linked to stock control and feeding; simple test methods should be considered (e.g. bioassays, using other fish as indicators), along with simple analysis (e.g. on Nessler scale, solids by Secchi disc) at the level at which the farmer can make decisions, with the possible back-up of NIFI workers.
Better stock control or production planning, e.g. by cropping fish out several times to make fullset use of pond production capacity, also by closer control of the size of fish in the system, both for feed calculations and knowledge of suitable harvest times (it appears that considerable risk occurs at late production stages, although fish are not growing). An empirical growth rate/feed rate/temperature/stock rate curve could be developed. An example of production planning considerations is presented in Figure 8.
Aeration: This would outwardly be the most simple way of maintaining oxygen levels and oxidising waste products to relatively harmless products. However, it is necessary to consider the amounts of oxygen required and the capacity of the ponds acting as aerobic systems to oxidise the wastes.
A basic approximation to oxygen required can be made on oxygen consumptions of other farmed fish, ie., 0.05 × feed rate dry matter (e.g. kg/day). Thus a pond of 0.1 ha with a stock of SMT (ie., 5MT/ha) of fish, fed at 3% body weight, will consume approximately 0.05 × 150 kg O2/day. The amount of oxygen required to oxidise wastes could be considered on the basis of BOD produced, which could be up to 10 times this figure; UOD (ultimate oxygen demand) is in turn normally greater than BOD, and here a total O2 input of 70–80 kg/day could be required. Preliminary results at NIFI, howevor, suggested that 10 kg/day would be required, though this may be because wastes were not being oxidised.
On the basis of conventional aeration supplying 10 kg O2/day, inputs of about 5 kw/hr are required for the more efficient units and hence a daily power requirement of 50 kw, which would cost ฿50/day for maintaining a stock of 5 MT. Overall operating cost would be ฿50 × 120 × 10,000 = ฿0.6/kg, plus approx. ฿0.1/kg capital charges for the aerator, on a 10MT final crop. If additional O2 is required for BOD removal, the cost will be correspondingly greater.
For emergency ceration use it could useful to consider setting up a long-tail pump to return water to the pond via splash boards or baffled troughs. This would save additional capital investment in aerators.
Encouraging photosynthesis: The possibility of maintaining photosynthetic activity, by reducing shading or preventing dominance by anaerobic species, might have some prospects, as only supplementary aeration may be required. Recent work in Ictalurus culture has shown that good daytime mixing can eliminate many of the problems of nighttime respiration by ensuring that oxygen-saturated water is moved to all strata during the day, and so overall energy requirements could be considerably less.
eg. 0.1 ha pond (assumed max. cap. - 10 MT)
| Time (mo) | av. wt./fish (g) | Theoretical capacity in numbers | Market Fish available (MT) as based on 100,000 seed input | |
| April | 1 | 10 | 1,000,000 | - |
| May | 2 | 33 | 300,000 | - |
| June | 3 | 66 | 150,000 | 0.8 |
| July | 4 | 100 | 100,000 | 2.6 |
| August | 5 | 150 | 66,700 | 10.0 |
Figure 8. Production plan for maintaining stocks in correspondence with theoretical carrying capacities and for yielding about 13.5 MT from a 0.1 ha pond through sequential harvesting in one grow-out cycle.
It would be useful therefore to examine more closely the occurance and distribution of planktonic species and water quality during the period of transition between aerobic and anaerobic activity. Thus toxic effects, for example, or substrate-imposed selectivity for anaerobic organisms could be identified and possibly corrected. A trial using aeration at this stage, to attempt to continue the period of aerobic activity would also be useful.
Other approaches to the problem of shading may be considered; it would be useful, for example, to test whether a stock of phytophagous fish, such as tilapia, or gourami could be kept in a cage within the ponds, to crop the plankton and reduce population densities. In a 0.1 ha pond, with a stock of, say 10ME of Clarias being fed at 2% body weight (dry food equivalent), about 100 kg of solid wastes could be produced per day. On the basis of Israeli observations on organic matter inputs, up to 50% of this weight could be obtained as fish, thus about 50 kg/day weight increment in fish stocks. Assuming an average stock of 5MT of Clarias, the average productivity of grazing fish would be 25 kg/day, or a 3MT crop over a 120 day growing period. At a safe stock density of 25 kg/m3, this implies a cage volume of 120 m3, or an area at average depth 1 metre, of 120 m2, 12% of the total area.
These figures are very rough approximations and a more sophisticated analysis of the productivity of the ponds in terms of the catfish wastes, and of the cropping rate by the planktophagous fish relative to plankton density, environmental conditions, temperature, etc. would have to be considered. Moreover, the greater sensitivity of these fish to poor environmental conditions night in turn necessitate a higher degree of control over the pond environment, and hence negate advantages otherwise obtainable.
Furthermore, it may be appropriate only to hold the amount of fish required to maintain the plankton below certain limits, as too heavy grazing would reduce the overall ability of the pond to metabolise Clarias wastes, and produce oxygen. Thus there may be an optimum density combining adequate light penetration and waste removal. As a preliminary trial, it would certainly be useful to test sample batches of e.g. tilapia fry in trial cages (e.g. 1 m3 wood and netting cages). Once the tilapia were large enough, say 30–50 g, and could be placed in cages with more open netting, any fry produced would escape and add to the feeding of the Clarias.
Filtration/Water Treatment: The concept of filtering replacement water or holding waste water, treating it, then returning it to the Clarias pond could be quite useful, though the main effect will be to remove solids from the water, NH3 and BOD being relatively unaffected, as there is in most cases insufficient oxygen for the filters to act in the conventional biological manner. The removal of solids, and the BOD associated with them, would of course improve the conditions in the pond, and if shading is a cause of difficulty, some photosynthsis could be encouraged, depending on the levels of solids found to be critical. The use of filters, however, would have to be considered carefully in terms of:
The available, or expected water source/quality.
The amount of use of the water source, and hence the solids loads on the filter (the amount possible depends on the void space of the material surrounding the plate) - if fine filtration is desired, capacity is less - typical ranges might be 50–500 kg solids/m3 - pumping power required increases as the filter blocks. Filling a 0.1 ha pond with water of initial solids concentration 400 mg/1 at a removal rate of 80% would yield 320 kg of solids. If interval between use is sufficiently large the solids will break down, through endogenous respiration, and the filter become more open once again.
In using a holding pond, the combination of filtration with aeration could improve the water quality considerably, though the earlier comments on the energy costs for aeration of this amount (i.e. BOD removal) should be noted. Furthermore, the capital costs of the filter installation ($500–$1000 in the experimental farms) make the economic feasibility questionable, unless the improved water quality is shown to affect yields noticeable. From the farmer's point of view, the additional capital costs, and lost revenue involved is setting aside a proportion of his land for reservoir use must also be considered, though a useful by-crop of tilapia could be obtained if these were stocked in the reservoir.
Until a clearer idea of the water quality limitations for the Clarias is obtained, it is difficult to determine the best size of reservoir pond, as the number of water changes required in the culture ponds, the quality of water supplied to the reservoir, and the time the water spends in the reservoir prior to use, will all have some bearing on the design. The operation of the reservoir may be approximated by comparison with conventional waste treatment lagoons or oxidation ditches, where a typical retention period of 5–10 days would be required. As solids would accumulate in the reservoir they would require regular removal. Possible layouts and cycles are shown in Figure 10.
Another way of providing reservoir capacity is to deepen the ponds. Provided the water is well mixed this should improve the overall ability of the pond to maintain water quality. Taking basic assumptions, a pond with depth of 2.5 m has a 66% increase in critical capacity over a 1.5 m pond.
Operation
sequential supply to ponds allows approx. 2 full changes per pond in a growing cycle as based on 10 day residence time in reservoir.
If supply is on a ‘batch basis’ it may be difficult to hold ‘clean-up’ fish stocks because of sudden water quality changes. Supply schedules can be adapted according to stock weights, etc.
Alternative
| A three-compartment clean-up pond
could be used; this may increase rate
at which wastes can be metabolised, and
provide a supply of good water for immediate
needs. Suitable for constant-flow. |
 |
Figure 9. Example layouts of systems for cleaning-up discharge water for re-use in rearing ponds.
Flowing Water: In areas where an irrigation water supply is available, the provision of flowing water of good quality can improve conditions considerably and wherever possible its use could be encouraged. The relationship between inflow and pond water quality is shown in Figure 10. If water has to be pumped, however, continuous operation may be too costly; at, e.g., 1 metre head, changing the water daily in a 0.1 ha pond, 1 metre deep, would require a power consumption of 250 to 500 w depending on pump efficiency, or ฿6 to 12 per day at ฿1/kwh, which amounts to ฿720 to 1440 per crop (120 days), or ฿0.07 to 0.14/kg of fish on the basis of a 10MT crop, plus capital costs of the pumps. Costs could be correspondingly more if water exchange was increased, as determined by inflow water quality and desired pond water quality.
A number of improvements have been suggested by NIFI staff involved in the Clarias studies; these are being tested and developed through the UNDP/FAO project. Some of these are being carried out through normal advisory work, while others are being developed in research or demonstration projects. They can broadly be separated into management and technical developments:
Management: Disease identification and control.
Pond water chemistry.
Artificial foods.
Technical: Use of aerators.
Filters for improving inflow water quality.
Use of storage ponds to pretreat inflow supplies or restore effluent water.
Much of the relevant research on problems in Clarias culture is already either planned or under way at NIFI. It is clear that the major strands of economic analysis, environmental requirements, and available water supply/quality must be brought together before technical measures can be considered for general application, particularly as the economic limitations may prove to be tight.
Figure 10. Theoretical concentrations of NH33 -N in a 0.1 ha Clarias pond (containing 1500 m3 water) in correspondence with three flushing rates (0.5, 1.0 and 2.0 volume changes/day).
| Stage in grow-out cycle | Wt. of fish in pond (kg) | Daily food input (kg/day) |
early | 1000 | 60 |
on-growing | 5000 | 150 |
harvest | 10000 | 200 |
One of the major points to emerge is the significance of pond management, and much of the research under way should yield the basic guidelines required for a better understanding of the inter-relationships involved in the production of Clarias.
The following is a summary of the recommended research, together with explanatory notes, where necessary.
Environmental Requirements
NH3 toxicity (also total ammonia) - currently under way. Haematology and histopathology would also be useful.
H2S toxicity (check function of pH, as toxicity probably due to H2S rather than HS).
Combined effects - using series taknks (see Fig. 11 - preferably longer-term - e.g. 60–90 days. Check haematology/histopathology.
Differences in ability to withstand conditions - fry not from stress-selected stock at present.
Pond Mass-Balances
Waste production - trash fish/dry food - e.g. use small tanks, weigh faeces, poss. digestibility studies.
Check whether urea output from Clarias rather than ammonia from food causes high NH3 conditions.
Benthic role - respiration rate, species, numbers present.
Plankton types/sizes, especially during aerobic/anaerobic changes.
Diurnal water quality variations, effect of feeding.
Water quality profiles (extent of mixing), check with waste outlet designs.
Overall stability and patterns of water quality.
Ultimate oxygen demands (UOD) of wastes/water.
Figure 11. Scheme for long-term research trials on effects of water chemistry characteristics.
Feeding and Growth
Optimum feeding rates and intervals (tank trials) and corresponding growth rates.
Effect of poor water quality.
Accuracy of sampling in field - as indicator for the farmer.
Actual growth rates.
Effect of gonadal development on growth.
Technical Trials
Aeration effects, e.g. mixing, oxygenation, overall water quality, effects on solids, henthos, photosynthesis, compare with theoretical predictions. Criteria for intermittent aeration. Actual cost.
Water replacement - check use of baffles to remove settled wastes. Compare results with theoretical predictions.
Water reservoir and filter - check removal rate of BOD, O2, SS, NH3, etc. Solids accumulation + filter cycle time. Actual cost.
Fish cages, etc. in production ponds and reservoir ponds-cropping rate, growth rates.
Water quality patterns in supply sources.
Production and Economic Assessments
Actual levels of risk, losses, profit.
Characterisation of present production methods.
Characterisation of water supplies available.
Overall market size potential (production/price relationships).
Evaluation of economic effect of technical improvements.
Other
Water analysis methods - simple indicators for the farmer.
Pond management guidelines - stock rates, feed rates, water changes, ‘danger signals’.
Use of pond mud - possible fertility value.
Given the resources currently available, it is obviously difficult to complete such a comprehensive range of studies, particularly where field trials are involved. However, most of the environmental requirement trials can be done at NIFI, also the waste output work, detailed benthic analysis, UOD and feed rate/growth rate trials, which together could contribute significantly to an understanding of the problems involved.
The Programme for the Development of Pond
Management Techniques and Disease Control
(DcF-UNDP/FAO THA/75/012)
REPORTS
THA/75/012/WP 1 1981 Report on Aquaculture Training Undertaken at the Inter- national Center for Aquaculture, Auburn University, U.S.A. Chanchai Sansrimahachai
THA/75/012/WP 2 1981 Third Semi-Annual Report (Sept. 1/80-Feb. 28/81) of Progress on the “Programme for the Development of Pond Management Technigues and Disease Control (DoF-UNDP/ FAO THA/75/012)” Alex N. Fedoruk
