1. INTRODUCTION
2. SOME GENERAL PROBLEMS AND THEIR SOLUTIONS
3. SHRIMP CULTURE IN PONDS
4. MILKFISH CULTURE IN PONDS
5. CULTURE OF MULLETS AND OTHER BRACKISHWATER FISH IN PONDS
The Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC) is one of the four regional lead centres participating in the Regional Network of Aquaculture Centres to carry out regional research, training and information activities under the UNDP/FAO Regional Project RAS/76/003. The main farming systems selected for studies at the Centre are: (i) shrimp culture in ponds, and (ii) pond culture of milkfish, mullets and other brackishwater fish.
Following the procedure adopted for formulation of research programmes of other regional centres, the Aquaculture Development and Coordination Programme (ADCP) assigned a task force to prepare an outline programme in consultation with the research leaders of the Centre, extension workers of the Bureau of Fisheries, and private farmers. The team consisted of Dr. K.W. Chow, Mr. H.L. Cook, Dean R.O. Juliano, Dr. T.V.R. Pillay and Dr. H.R. Rabanal. Dr. C. Lim and Dr. C.T. Villegas of the SEAFDEC Aquaculture Department, and Mr. R. Edra and Mrs. S. Seville of the Philippine Bureau of Fisheries and Aquatic Resources (BFAR) also participated. The task force had opportunities to discuss with some of the leading fish pond operators (Mr. C.S. David, Mr. C. de los Santos, Mr. T. Jamandre, Jr.) the major problems currently faced in brackishwater pond farming and the type of assistance they expect from research institutions. It was also able to study a list of problems for research in brackishwater aquaculture that the Iloilo Fish Producers Association, Inc. had submitted to the SEAFDEC Center. Some of the senior research workers of SEAFDEC (Dr. F. Pascual, Mrs. J.H. Primavera, Dr. F. Lacanilao, Dr. L. Benitez, and Mr. M. Lijauco), and of the University of the Philippines (U.P. College of Fisheries) Brackishwater Aquaculture Centre in Leganes, Iloilo (Dr. A.S. Camacho and Dr. R.D. Fortes) and Dr. N Hoshino of SEAFDEC attended discussions on certain aspects. They reported on their on-going and proposed investigations. The task force had several discussions with Mr. Felix R. Gonzales, Director of BFAR, concerning details of the organization of research and training under the regional project.
The SEAFDEC Aquaculture Department is currently in the process of reorganization and considerable streamlining of its varied activities is expected. The Department had prepared a list of selected research projects to be implemented in 1980. It is of special interest to note that this list was prepared in consultation with some of the leading fish pond operators in the area and is based on problems encountered in commercial-scale farming. The task force could therefore use this as a basis for considering longer-term research needs and possibilities of multidisciplinary approach for problem solving.
The general time-frame considered for the research programme was, as in the case of other regional centres under the project, a two-year start-up period followed by a five-year period of concentrated research. The task force has identified research needs and proposed research approaches. It is envisaged that the detailed design of studies and experiments will be prepared by designated research teams with the help of international consultants as required.
The SEAFDEC Aquaculture Department has specialized laboratories for research on many disciplines involved in aquaculture, although all of them do not have adequate staff with the required training and experience. The quantum of trained staff is increasing as a result of the staff training programme initiated in earlier years. The collaboration that has been developed with the U.P. College of Fisheries has made it possible to utilize a certain number of graduate students for individual investigations.
There is a need to increase or improve the scientific manpower of the Department, and the task force feels that this can be accomplished through:
(a) assignment of international experts, mainly on a short-term basis to plan and initiate research and making available their services, if need be, during the course of investigations to solve problems faced in the studies and/or towards the end of the investigations to evaluate and interpret the results;(b) arrangement for short-term training of researchers in other institutions in specific research techniques; and
(c) secondment of associate scientists from other participating countries of the regional project under the programme of Technical Cooperation among Developing Countries (TCDC).
Among the disciplines in which the Department needs strengthening are: aquaculture engineering and pond management, nutrition and feed development, diseases and health of cultivated species, and economics. It will be necessary to obtain specialized external assistance to build up the necessary facilities and manpower for effective multidisciplinary research and guidance.
The need for multidisciplinary approach and team work for solving problems has been now well recognized in the Department. Such team work has to be further developed, particularly in yield trials where the effect of several interdependent variables can be studied simultaneously, if the experiments are properly designed and carried out by teams of specialists. Special mention has to be made of the need for incorporating economic evaluation in the design of all relevant experiments. Such a procedure may enable the maximum use of available production pond facilities in the farm leased by the Department at Leganes.
It is necessary to increase the number of production ponds for conducting factorially designed experiments. On the completion of the current negotiations for the extension of lease for the Leganes farm, it is hoped that additional production ponds can be constructed, with funds requested for this purpose from the Government of the Philippines. The additional ponds will enable expanded yield trials, with adequate numbers of replications.
Most of the laboratories of the Department seem to have the essential equipment for the type of studies proposed to be carried out. The only major item of equipment considered necessary on a high priority basis, is a feed mill to produce the required quantities of feeds for production experiments.
There are some problems common to all systems of pond farming in brackishwater environments. One of the most important among these is the nature of the soil in which ponds are built. Most of the tidal flats and mangrove swamps that are used for pond construction have highly acidic soils. Ponds built on such soils show retarded growth of benthic organisms that have to be raised as food for milkfish, mullets and shrimps, as also poor water quality, causing large-scale mortalities. Leaching of sulphates from the soil by repeated flushing, followed by liming and organic fertilization, are the only methods presently available to remedy this condition and it may take four years or longer before a pond becomes sufficiently productive. This imposes a major economic burden on the farmer and adversely affects the feasibility of most types of pond farming in brackishwater areas. Recent work in the U.P. Brackishwater Aquaculture Center has provided some useful information on chemical processes in acid sulphate soils, including nutrient release and its effect on algal growth. In view of the importance of the problem, there is a need for concentrated research to develop more rapid methods of pond soil treatment.
Culture in brackishwater ponds has traditionally been based on the production of lab-lab or benthic algal complex, for which appropriate water management has to be practiced. Generally the water level has to be kept shallow. Raising of an adequate crop of the desired species of algae by proper fertilizing with organic or inorganic fertilizers or a combination of the two plus water management, and maintaining the crop at the required level, needs considerable skill on the part of the farmer. Fertilizers, both organic and inorganic, are becoming either scarce or too expensive. There is, therefore, now a trend towards the use of artificial feeds, particularly as a supplement to natural foods.
The cost of fertilization is not always as low as is often believed; in brackishwater ponds in the Philippines, it is reported to vary between 25 and 60 percent of the cost of fish production. Agricultural waste products or other feed stuffs are now used as supplemental feeds wherever available, without any processing. Preliminary experiments have shown that milkfish and shrimp can be fed moist as well as dry pelleted feeds. However, a major constraint remains the availability of processed feeds.
Aquaculture has invariably to compete with the more established livestock industry for feed ingredients. Furthermore, unlike commercial animal husbandry, commercial fish farming in the region is not served by an efficient feed processing industry. Fish feeds, when used, are mostly prepared at farm sites, often lacking adequate facilities for quality control of diets. Also, the choice of feed ingredients available to the fish farmer is limited and, because of the smaller quantities involved, have to be purchased at higher prices. Both these factors increase the cost of the prepared feeds. Other problems associated with feed development are: (a) inadequate knowledge of the nutritional requirements of the species under culture, and (b) very limited knowledge of the nutritive value of indigenous feed ingredients. This necessitates the provision of wide margins of safety for setting nutrient levels as well as for the use of locally available ingredients in diet formulation.
Fish feed development that meets the objective of producing efficient composite diets from-local raw materials, therefore, merits high priority in brackishwater aquaculture research in the region. Detailed surveys of the availability and cost of feed ingredients, and laboratory studies to determine the nutritional requirements of the cultured species, will have to be carried out to provide the basis for feed development.
A third common problem of significance in brackishwater pond farming is water management. Traditional forms of brackishwater pond culture have depended on tides for filling and draining of ponds. However, in many situations, pumping has to be resorted to for water management and the present fuel costs make this extremely expensive. It will greatly benefit aquaculture if alternative sources of energy can be found for pumping. The results of some of the on-going work in certain centres for the development of solar or wind-driven pumps could prove valuable for aquaculture Pumps and windmills developed for irrigation could be modified, if necessary, and tested for filling and draining fish and shrimp ponds. The use of such unconventional energy should also be tried for aeration of ponds as well as for the operation of indoor hatcheries and rearing systems.
A problem common to most forms of brackishwater aquaculture is the lack of adequate economic data necessary for the evaluation of culture techniques and for development planning. The optimum size of ponds and the minimum economic size of farms have yet to be determined. While the most suitable size of ponds will have to be decided on the basis of a sufficiently large number of comparative experiments, extensive data on commercial operations will have to be collected for evaluating the minimum required size of farm under a given set of conditions to yield the best cost-benefit ratio.
In the traditional brackishwater pond culture of shrimp, widely practiced in Asia, production is dependent on the seasonal abundance of wild fry. In many cases, the ponds are very shallow and water temperature and salinity become so high that large-scale mortality occurs. Predation by extraneous fish that gain access to the ponds also accounts for considerable loss of shrimps. Fertilizers and feeds are not generally used and as there are no suitable feeds available, production depends almost entirely on natural fertility. Consequently, yields are low, generally in the range of 100 to 300 kg/ha/year.
Some improvements in the traditional method of culturing shrimp have been evolved. For instance, by providing increased water depth in ponds more favourable temperatures can be maintained and mortality reduced. Production can be raised by increasing the stock density in ponds by catching shrimp from the wild and then stocking them in ponds. It has been demonstrated that nursery rearing of post-larvae before stocking them in growing ponds results in increased survival. This will undoubtedly result in increased yields, but production will still remain relatively low until research provides solutions to other more complex problems which limit production.
One of the most critical aspects is the availability of post-larval shrimp for stocking. It is generally very difficult to find a dependable source of post larvae for large-scale operations. When there is a scarcity of fry, as in the case of tiger shrimp, Penaeus monodon, the price becomes very high. When the fry are expensive they are stocked at a low density and grown to a large size. This increases risk considerably. If cheap fry were available, it would be possible to stock ponds at higher densities and harvest at a smaller size after a shorter growing period. Of course, the relative economic advantage of one system over the other must be considered, but at the present time, there is no option due to a lack of fry.
Considerable research has been done for developing shrimp hatcheries within the region, but procedures for commercial-scale hatchery operations are not yet fully developed. Present hatchery methodology utilizes live foods and as there are many problems concerned with their use, it will be advantageous to develop artificial feeds for use in the hatchery. In recent years progress has been made in maturing broodstock in captivity through the use of eyestalk ablation, but the percentage of females attaining maturity and the number of viable eggs obtained from them are still low.
Traditional shrimp culture is based on a number of species, and even in improved systems there may be benefits in using more than one species. For example, even though P. monodon is generally considered to be the best species for culture in the region, it may not be the most suitable species to grow in all locations at all times of the year. There are indications that in high salinity ponds, P. indicus might provide a higher return, and Metapenaeus ensis might be more suitable for low salinity ponds. Other factors to consider are that maturation in captivity is easier for some species than for others and that susceptibility to disease varies greatly from one species to another. Analysis must be made of the various trade-offs possible to evolve the most economic systems.
It is generally recognized that yield can be increased by increasing the natural productivity of ponds to supply increased amounts of food. There is sufficient information on how to promote growth of the benthic blue-green algae in shallow ponds. Unfortunately, this shallow type of pond is not suitable for growing shrimp because of the high temperature of pond water. Experimental work done so far has not led to reliable means of increasing the productivity of plankton in deeper brackishwater ponds. Such basic information as the proper ratio of nitrogen to phosphorus, and dose, frequency of application, remains to be determined.
Direct feeding is another way of increasing yield. However, adequate knowledge of the nutrient requirements of the various species of shrimp, necessary for formulating efficient diets, has yet to be obtained. Feeding, to date, is based almost entirely on waste or surplus products such as trash fish. These feedstuffs are not very efficient and if used in quantity tend to cause management problems by fouling the water.
In traditional forms of extensive shrimp culture, very few disease problems have been recognized. However, with the adoption of intensive culture methods, disease has become a major problem, especially in hatchery operations. Shrimps seem to be subject to infection by a variety of diseases, including bacterial, protozoan, fungal and viral infections. In many cases catastrophic mortalities occur. One very common occurrence reported in the region for which no causitive factor has been identified is persistent soft shell condition of shrimp grown in ponds.
Based on the problems encountered so far in the field, the needs for research on shrimp culture can be categorized into five, viz, hatchery development, development of nursery systems, improvement of grow-out systems, nutrition and feeds, and health. The specific needs are listed below. Besides these, genetic studies could play a major role in improving shrimp culture, but it is essential to determine in advance the objectives of genetic manipulation and the characters that need to be studied such as easier maturation, growth rate, food conversion, resistance to disease, etc. for obtaining useful results. The task force was of the view that studies of this nature should await progress in some of the other aspects, which would provide the basis for determining its orientation.
Besides Penaeus monodon, the proposed research will cover other species widely distributed in the region, including P. indicus, P. semisulcatus, P. merguiensis and Metapenaeus ensis.
The major research needs are:
(i) Refinement of techniques for (a) maturing broodstock in captivity, and (b) hatchery operation.(ii) Improvement of traditional earthen pond nursery system, with special reference to production and maintenance of food supply and water management.
(iii) Development of tank or raceway systems for intensive post-larval rearing, using artificial feeds.
(iv) Determination of chemical parameters of importance in the productivity of production ponds and their inter-relationships
(v) Methods of improving the management of production ponds, including pond preparation, control or elimination of pests, predators and competitors, and pond aeration.
(vi) Development or comparison, including economic studies, of grow-out systems, viz, 'plankton pond' culture, 'lab-lab pond' culture and pond culture with intensive feeding.
(vii) Determination of the relative efficiencies and economics of monoculture and polyculture.
(viii) Improved methods for mass production of algae and zooplankton as food in hatcheries and nurseries.
(ix) Study of etiology and treatment of diseases and health problems of shrimps in hatcheries, nurseries, and production ponds and the development of methods for regular health monitoring in culture establishments.
As mentioned earlier, the proposed research, plus field surveys and observations, need a multidisciplinary approach, involving team work by specialists in the disciplines concerned. Since many of the factors to be studied are inter-dependent, it should be possible to study a number of parameters simultaneously, so as to obtain reliable results and to make the best use of research facilities and personnel.
Most of the shrimp culture research in SEAFDEC has concentrated on P. monodon. It has been recently expanded to include P. indicus and P. merguiensis, may be started in the near future. Work on P. semisulcatus may be started in the near future.
The age of broodstock and their nutrition are two aspects that should receive attention in efforts to improve the percentage of individuals that respond to the eyestalk ablation method for maturation! Brood shrimps of different age groups fed with different live and compounded feeds may be used for maturation studies. The feasibility of maturation in ponds and in net cages installed in ponds should be tested and comparison made with maturation and spawning in tanks.
The effect of water quality on maturation, hatching and larval survival as observed at typical hatchery sites, will have to be evaluated to develop reliable criteria for selecting hatchery sites. Development of a suitable artificial feed for larvae should receive high-priority attention. The efficiency of artificial feeds should be evaluated not only in terms of growth, condition and survival of larvae, but also in terms of the economics and convenience of operations. Through appropriate experiments, the effect of different variables such as tank size and design, larval density, feeds and feeding, and management procedures should be evaluated. The conditions under which infections such as that caused by the fungus Lagenidium sp. became epidemics should be determined and suitable control measures tested.
For the improvement of nursery systems, comparative tests of different tank and raceway designs will be needed. The relative efficiencies of indoor and outdoor nurseries have to be determined. Efforts may be made to increase the optimum stocking density of post-larvae by providing additional substrates for growth of natural food in nurseries. Based on experimental studies, widely applicable nursery management procedures should be evolved.
In studies aimed at the improvement of grow-out systems, the advantages and disadvantages of polyculture of shrimps with milkfish or other finfish should be evaluated. The use of deeper ponds with intensive feeding, and ponds with fertilization and only supplementary feeding, should be compared with mono- and polyculture in shallow lab-lab ponds, with and without supplementary feeding.
When feed development work has made sufficient progress, more intensive systems of farming with complete feeding and aeration can be tried, particularly with quick-growing species like P. monodon.
Experimental work incorporating appropriate economic evaluation will be necessary to test the feasibility of increasing the number of crops of quick-growing species such as P. monodon in grow-out ponds, by reducing the growing period and harvesting the shrimps at a smaller size. The feasibility of rotating the culture of different species of shrimps based on seasonal changes in salinity and temperature conditions should also be tested.
To determine the causes of some of the health problems like soft shell condition, both field observations (on water quality changes, feed and feeding) and controlled experiments will be needed.
4.1.1 Seed production and supply
4.1.2 Sites for ponds
4.1.3 Pond management techniques
4.1.4 Food and feeding
4.1.5 Pond design and engineering
4.1.6 Causes of mortality
4.1.7 Economics
4.1.8 Polyculture
The milkfish (Chanos chanos) is a widely cultivated species in Indonesia, the Philippines, and Taiwan (China). Some 200 000 ha in Indonesia, 180 000 ha in the Philippines, and 30 000 ha in Taiwan or an overall total of 410 000 ha are being utilized for farming milkfish. The average annual production in these areas varies from 500 to 2 000 kg/ha/year; a total production of 286 000 metric tons per year is estimated for the entire region.
The culture techniques used are generally of the extensive type, characterized
by minimum inputs and consequently low production. Although the industry is
well-established, efforts to maximize production and increase return on investment
have been hampered by a number of constraints.
The seed used for culture comes from the wild. As the species does not breed in ponds, some research institutions have devoted attention in recent years to its induced breeding by hormone administration. SEAFDEC Aquaculture Department has achieved some success in breeding the fish under experimental conditions, and a small number of fry obtained by induced breeding have been reared to adults in ponds. However, much further studies are needed to develop dependable methods for the mass production through induced breeding and hatchery rearing.
The availability of fry in natural collection grounds fluctuates widely from
year to year, making supplies erratic. Also, the survival of wild fry is often
poor. It is estimated that an average of 30 to 60 percent mortality occurs between
capture and completion of nursery rearing. Fry catching gear often cause stress
to the fry, resulting in high mortalities. Deficiencies in handling and storage
techniques after capture, are also believed to cause additional mortalities.
This high mortality, compounded by uncertainties in their abundance in collection
grounds, leads to critical shortages of fry.
Even though during the last two decades culture of milkfish in net pens in a eutrophic freshwater lake has attained commercial proportions, the most common method continues to be pond culture.
Mangrove swamps, estuarine areas and open tidal flats are the sites generally utilized for the construction of milkfish ponds. The use of mangrove areas as fishpond sites is a subject of some controversy as it is believed that such areas serve as breeding and nursery grounds for species which are economically important in capture fisheries, especially the penaeid shrimps, and some finfishes. Utilization of these swamps for fishpond construction in the region varies from as high as 40 percent (Philippines), to a fraction of a percent (Indonesia, Malaysia). There is now an increasing understanding of the type of mangrove areas that should be conserved as nursery grounds or for environmental reasons and the areas that can be utilized for fishpond development without environmental damage.
The problem of acid soils in brackishwater ponds has already been referred
to. Water quality is another factor of major importance in pond management.
It is believed that poor water quality has probably caused greater mortalities
than predators and diseases.
While a number of pond management techniques and variations of these are presently
in use, two of them can be considered as predominant. One is based on the use
of benthic algae in relatively shallow ponds or the 'lab-lab method', and the
other is based on the use of plankton in relatively deeper ponds or what may
be called the 'deep water' or 'plankton method'. Very often these two methods
are used in succession. Operations of both methods may be affected by site elevation,
pond design, prevailing weather, and management practice adopted by the operator.
Filamentous algae or lumut method in medium-depth ponds used to be one other
management technique, but this has now been practically discontinued. Because
of the shallow depths in lab-lab ponds, there are space limitations. It cannot
be easily practised in areas where there are no distinct dry and wet seasons.
Maintaining a good growth of lab-lab calls for special skill on the part of
the farmer in water management and fertilization. The plankton method is of
more recent origin. While encouraging results have been obtained in some instances,
there are cases when the anticipated high production could not be obtained.
The reasons for this have yet to be ascertained.
In the wild, larvae of Chanos chanos feed primarily on zooplankton. Older fry also feed on phytoplankton. Chanos chanos under culture, subsist on plankton or benthic algae (lab-lab) depending on availability. The development of gill rakers of fry has not been closely studied to determine at what stage they become fully functional and to what extent the fry can utilize various species and sizes of planktonic organisms.
In some places, fry caught in the wild and stocked in ponds are often fed cooked egg yolk for 5 to 7 days. Afterwards the young fish feed on phytoplankton or algae maintained at suitable levels by fertilization of the ponds.
In grow-out ponds, artificial supplementary diets consisting of such common feed ingredients as rice bran and oil seed meal, have been tested with variable results. Data on growth rate and feed efficiency when fed on artificial diets are very scanty. Knowledge on the nutrition of the species is also very limited.
As mentioned earlier, the species has been spawned in captivity, but the survival
of larvae and fry is still very low.
Traditionally, ponds for milkfish were crudely constructed and were not based
on sound engineering principles or design. However, in recent years, different
layout plans, construction specifications and designs are being adopted to improve
management. Development of more definitive criteria for site selection and pond
construction under different land elevations, tidal characteristics and soil
and vegetation characteristics, remains to be done.
Deterioration of water quality is a major cause of milkfish mortality in ponds. Studies that can lead to the development of standard techniques to prevent mortality are required.
Under current management, mortalities due to predation still occur. This has been partly solved through techniques, including the use of chemical pesticides, which in turn have now become a problem of significance.
Mortalities due to diseases and parasites are believed to be rare in pond culture
of milkfish. However, with the increase of stocking rates and intensification
of culture, there is every possibility of increased mortalities. It is also
suspected that some of the unexplained mortalities presently occurring may be
actually caused by diseases, which go undiagnosed due to lack of know-how.
In spite of the long existence of the industry, detailed economics of the farming systems as a whole, or of the operations involved such as fish seed production, nursery, grow-out, etc. Or the management innovations (fertilization, feeding, etc.) have scarcely been studied.
The most economic size of production ponds, or the minimum economic size of
pond farms have yet to be determined.
Even though traditionally the practice has been monoculture, the extensive nature of operations led to a form of polyculture as evidenced by the presence of sizeable quantities of extraneous species in harvests (e.g. shrimps, mullets, siganids, seabass, grouper, spadefish, tilapia, etc.). In recent years many farmers have adopted some form of intentional polyculture However, this is not based on proven biological principles. Optimum stocking rates and appropriate species combinations have not yet been determined.
(i) Studies to reduce mortality of milkfish fry obtained from the wild through improvement in capture gear and methods of handling and storage.
(ii) Development of methods to reduce mortality in the nursery stage by using new rearing techniques and proper feeds.
(iii) Studies to compare relative effectiveness of culture in grow-out ponds based on natural food dependent on natural fertility alone and/or with fertilization to grow benthic algae in shallow ponds (lab-lab method), and with fertilizers to grow phytoplankton in deep water ponds (plankton method).
(iv) Studies to determine the economies of new innovations in design (modular or progression) and other improvements in pond layout (reduced area, increased depth, provision for water circulation in canals, etc.).
(v) Development of techniques of milkfish/penaeid shrimp polyculture
(vi) Development of rapid and more efficient methods of conditioning acid soils for milkfish culture.
(vii) Determination of the causes of unexplained mass mortalities through studies on water quality, control of predators and identification and prevention of diseases.
(viii) Studies on the species composition of natural food and their relative contribution in milkfish nutrition.
(ix) Development and testing of artificial larval diets to replace natural live foods.
(x) Development and testing of balanced diets or supplemental feeds, using readily available and inexpensive indigenous feed ingredients.
(xi) Development and testing of artificial diets for broodfish.
(xii) Investigations on management and economics of feeding in a semi-intensive Culture system, using supplemental feeds.
A wide variety of research activities are involved and the lead centre may have to use, beside its own facilities, farm facilities of the BFAR Extension Centres and of private operators in the country, to carry out the necessary experiments and testing. Close collaboration of the U.P. Brackishwater Aquaculture Center is envisaged for certain studies. SEAFDEC has an on-going programme of research on milkfish culture, hatchery, natural seed production and pond culture, supported by IDRC. The research approach described below relates to the directions in research to be done on a medium/long-term basis in the region. The continuation or expansion of the support for the proposed research from IDRC or other agencies is expected.
(i) Research to reduce mortality of fry obtained from the wild during capture, or Storage and in nursery rearing can be done in stages as follows:
(a) Study of existing fry-catching gears and development of new gears for increased efficiency and reduction of stress on the fry.(b) Study present methods of handling, holding, transport and storing of fry to develop methods for increasing survival by improving water quality and by feeding.
(c) Develop better nursery techniques.
(ii) Detailed studies will be conducted to compare the two management methods (lab-lab method and plankton method) in grow-out ponds.
(iii) Improvement of grow-out methods will be attempted through:
(a) Better understanding of the chemistry of acid sulphate soils, based upon which more effective soil conditioning can be developed.(b) Identification of water quality conditions that promote most suitable natural food of milkfish.
(c) Diagnosis and control of diseases and eradication of pests.
(d) Development of effective methods of fertilization for brackishwater ponds.
Based on the results of experimental work and the experience accumulated by the industry, criteria will be developed for site selection and pond designs for milkfish farming, including appropriate size of ponds and minimum size of farms under given conditions.
(vi) Development and evaluation of feeds for larvae and fry. Studies will be made to determine the stage at which gill rakers become fully functional for the purpose of improving feeding procedures.
(v) The development of suitable artificial diets for fry and fingerlings will entail the following: (a) determining the nutrient requirements and metabolism, and studies on digestive enzymes in response to feeding; (b) evaluation of hitherto untested, inexpensive, and readily available feed ingredients of known nutrient composition for acceptability by the species followed by least-cost formulation of practical balanced diets incorporating these new feed ingredients; (c) applying feed processing technology to produce diets that possess commercial attributes and are acceptable in form and size to the animals; (d) testing of experimental diets and measuring growth rates and feed efficiency; (e) development of feeding techniques and designing dispensers for such artificial feeds; and (f) evaluating the cost effectiveness of artificial feeding.
(vi) Development of artificial diets for broodfish with the purpose of inducing early sexual maturity.
(vii) The economics of feeding supplementary artificial diets along with plankton and benthic algae will be studied to determine the cost effectiveness.
(viii) Comparative experiments to determine whether polyculture of milkfish with shrimps, or mullets, will be advantageous from the point of view of productivity or economic benefit.
While milkfish farming is a well-developed industry, it is largely restricted to the Philippines, Indonesia and Taiwan (China). Its acceptance as a food fish being restricted in the region, the task force also considered the culture of other brackishwater fish that have regional importance. Although not extensively practiced within the region, mullet culture is of some significance at present, and has potential for development in most countries of the region. It is much more widely accepted as a food fish than is milkfish.
There are many species of mullets, some of which are slow-growing or attain only a small size. The most widely distributed and fast growing species is Mugil cephalus and this species has been the focus of studies in a number of research institutions around the world. M. cephalus does not breed in the confined waters of ponds and most of the culture presently done is based on wild fry collected from estuarine and foreshore areas. The species has been induced to breed by the administration of pituitary and other hormones and sometimes only by environmental manipulation. Larvae have been reared under experimental conditions, but very high mortality occurs from the critical period when the yolk absorption is completed to about the 40th day after hatching. The reasons for the mortality are not yet determined. Fry of experimentally bred fish have been grown in ponds to adults fed with natural food and supplemental feed. However, this type of culture is still in the early stages of experimentation. The widely adopted system of culture is based on naturally occurring fry, which can be collected in large numbers in most areas. In the early stages of their life, it is often difficult to distinguish the different species. A dependable and rapid method of fry identification and sorting has yet to be developed, to enable the rearing of only selected species.
There are strong similarities between milkfish and the major species of estuarine mullets in their habits? including tolerance of salinity and feeding habits. Therefore, the design of ponds, fertilization and feeding methods and general pond management measures adopted for the milkfish seem to be applicable also to mullets. The nursery and production experiments proposed for milkfish will have to be repeated in the case of mullets. There is also the need to make comparative studies of culture in the so-called plankton and lab-lab ponds' to determine their relative efficiencies in productivity and economics. Although more than one species of mullet may have to be cultured together for reasons of availability of fry, there does not appear to be a strong case for polyculture with other species of fish commonly cultivated in the area, as they also have similar feeding habits.
Among species other than mullets that are of regional interest, the most important appears to be the seabass Lates calcarifer, which can be cultivated in brackish- as well as fresh water, grows well if fed adequately and has wide acceptability. It is a carnivorous species and would require suitable feeds, such as trash fish or compounded feeds, for culture. Alternatively, it may be possible to combine its culture with that of a forage fish, such as tilapia. The seabass is a relatively high-priced species, and therefore very attractive for commercial-scale culture or small-scale culture operations meant for increasing the income of small-scale farmers or fishermen. In many areas fry can be collected from estuarine and coastal areas. The species has been bred under captivity and hatchery procedures have been successfully adopted. Large-scale commercial hatcheries are now being developed in Thailand.
(i) Development of methods for controlled reproduction of quick-growing species of mullets and mass rearing of their larvae.
(ii) Development of rapid and practical methods of fry identification and sorting, pending the development of controlled reproduction and hatchery production of seed.
(iii) Determination of the type of ponds (lab-lab type versus plankton type) most suited for mullet culture and the applicability of milkfish pond management procedures in mullet farming.
(iv) Development of compounded supplemental feeds for mullets and their evaluation.
(v) Methods of monitoring health and disease problems of mullets and disease control.
(vi) Refinement of controlled breeding of seabass and techniques of larval rearing.
(vii) Collection, conditioning and transport of seabass fry from natural habitats.
(viii) Development of nutritionally adequate and economically acceptable artificial feeds for seabass.
(ix) Culture of seabass to marketable size with tilapia as forage fish.
(x) Culture of seabass with artificial feeds and evaluation of the economics of the practice.
(xi) Methods of monitoring health and disease problems of seabass and disease control.
Work is already underway in SEAFDEC on induced breeding and larval rearing of Mugil cephalus. This should be intensified and extended to other quick-growing species available in the area. Special attention has to be devoted to determine the causes of poor larval survival. Specially prepared larval feeds should be tried to determine whether larval mortality can be reduced by improved feeding.
Until such time that suitable methods for large-scale hatchery production of mullet fry become possible, it will be necessary to use wild fry for culture experiments. Attempts should be made to develop methods of fry sorting based on information on the seasonality of occurrence in nature and gross morphological characters. If this does not prove successful, growing the fry to a stage when they can be sorted by species for stocking production ponds will have to be tried.
As stated earlier, the research approach proposed for milkfish culture can be adopted with very little modifications for grow-out studies on mullets, both in mono- and polyculture with shrimps. Comparison of the economics of culturing large and small mullets should receive special attention, because of the problems of availability of the fry of desired species in different areas.
Work on seabass has to Start with the testing of techniques already developed elsewhere, The results of work on larval feeds in the Centre are expected to prove valuable in refining methods of hatchery production of fry.
The development of a suitable compounded feed based on locally available ingredients should receive high-priority attention, as trash fish, which is often used as feed in some areas, may not be readily available elsewhere. As an alternative, the production of forage fish in seabass ponds, or their production in separate forage fish ponds for feeding seabass, should be investigated.
Determination of stocking densities in nursery and production ponds, pond design and pond management measures, and health and disease studies, will be required to recommend suitable culture procedures. Economic evaluation should form an important part of each of the investigations proposed.
