After reaching a rough consensus on priorities among the commonly cultured groups of aquatic species, the aquaculture experts of the sub-groups on research priorities, agreed to prepare short summary descriptions of the research needed on each species group in order to provide more substance to the recommended priorities. These descriptions, which were discussed and accepted by the sub-group as a whole, are reproduced here.
Introduction
The culture of Tilapia species in ponds in tropical and sub-tropical countries, using agricultural by-products and manures as pond inputs and yielding two to three crops totalling 5 000 or more kg/ha/year, has been demonstrated to be feasible and economical. Presently, for small-farm or low-cost-input culture, tilapia show greater potential in these geographical areas than any other food fish. Although a great amount of technology has been developed for tilapia culture, great variation in resources and environmental conditions throughout the world warrant further research to determine how best to optimize tilapia production under specific area conditions.
In Africa alone, the potential yield of tilapia was projected at 8 × 106 tons (Spoleto meeting). Potential for culture of this fish is equally impressive for tropical and sub-tropical Latin America and Asia. The fact that profitable culture of tilapia has already been demonstrated in many areas of the world and this fish has great potential as a relatively low-cost food indicate that tilapia culture should receive high priority research attention.
Seed production
Research into various areas related to seed production is the highest priority area. Africa alone will have a potential need for five thousand million fry per year (Spoleto meeting). Research areas include hybridization to produce monosexual seed stock, genetic selection, induced maturation and hormone treatment.
Feeds and natural foods
This area deserves high research priority because of its great influence on yield and production costs. Research should be primarily of an applied nature since most tilapia culture will be in ponds and, fortunately, tilapia can receive significant amounts of nutriment from both pond organisms and supplemental feeds. Management practice influences the natural food available. Supplemental feeds vary greatly among areas, from concentrated to crude sources of nutrients. Because of the great variation in management practices and availability of supplemental feeds, more research on the nutrient contributions from these two sources and the interaction of them is needed. Research on feeding practices and basic nutrient requirements should be further pursued.
Culture systems and their management
This area deserves high priority. Although a number of technologies for tilapia culture have been developed, which have considered such variables as species, stocking density, pond enrichment, supplemental feeding, polyculture, production schedule and water source, the optimum culture and management system for the resources and environmental conditions in a given area must be determined. Development of pilot or demonstration culture systems in the area will be of great value. Management methods to compensate for reproduction in culture ponds (hand-sexing, selective harvest, etc.) are an important research subject.
Genetics
Closely associated with the seed production is the need for genetic selection of strains and the production of polyploid, fast-growing tilapia. The potential for experimental hybridization after induced breeding and fertilization are clearly enormous. The fact that F1 all-male hybrids resulting from certain crosses usually grow faster means that the potential of looking at the hybridization of the many species available is a huge untapped resource.
The exploitation of waters for Tilapia aquaculture will benefit from genetic selection for tolerance to environmental factors such as temperature and salinity.
Integration with other crops
This area deserves high priority. Combining tilapia culture with livestock or poultry raising, by allowing the fish to benefit from the wastes from the land animals, has been found to be feasible and economical in serveral areas. Technology for using this culture system should be developed for each area condition. Rotating or a combination of tilapia and rice has great potential in many tropical areas and technology should be developed.
Fish health
This area should receive intermediate priority. Tilapia are relatively tolerant to intensive culture, enriched water conditions and fish health is generally not a major problem. However, pathogens indigenous to certain geographic areas should be investigated. Algae toxins have caused mortalities and should be researched. The effect of metabolites found in highly eutrophic ponds on the health of tilapia should be examined.
Members of the family Cyprinidae of global significance that are cultivated in many developing countries are Chinese and Indian major carps and common carp. Several local tropical cyprinids started to be cultivated more recently. Total annual production of this group of fishes through aquaculture is estimated to be at least 2 million tons. It was felt that culture of these species has a very high potential for a large increase in finfish production in developing regions within the next ten to fifteen years. Even a moderate increase of yields in existing ponds (for instance from 1 000 to 1 500 kg/ha) could cover a significant part of protein need in some countries. The common practice to market live fish is an additional advantage which eliminates the needs for expenditures on freezing, processing, etc.
While pond culture certainly has the greatest potential for production increase, other systems (cage and pen culture, ranching in lakes and reservoirs, as well as integration with various animal husbandry systems, irrigation systems or land crops) have also a promising significance.
Of the discipline-oriented research areas considered to be of global relevance for inputs into culture system research, the priority should be given to health protection, seed production and foods. While genetic research may not result in an immediate substantial production increase, it has significant long range potential.
Research on management of ponds and other culture systems should be considered as highly significant.
To improve seed production, criteria and methods for selection of good quality broodstock, improvement of hatchery techniques and methods for nursing of fry and fingerlings should be developed through research.
Research on health protection should provide methods and means for reduction of losses during all phases of production, from obtaining eggs to cropping of marketable fish. Such losses are at present either lowering the efficiency of the culture systems or constraining them significantly. Very little is known now about their causes in tropical countries. Viruses that are, for instance, an important group of fish pathogens in developed countries, have not been searched for in the tropics. The research should be oriented toward development of laboratory diagnostic methods for health monitoring, the study of disease entities and the incorporation of prophylactic and treatment measures into production technologies.
Local feedstuffs suitable as fish feed, the knowledge of nutritional requirements of various carps, supplementary and complete diet formulations, feeding rates for various species at different temperatures, and other nutritional studies, are urgently needed for increased yields and improved economy.
Interdisciplinary studies of pond management (stocking densities, species combinations, fertilization, manuring, health protection, feeding, water management and effects of interactions among these factors on yields and environmental parameters) and mangement of other production systems are essential for obtaining data for shaping up most suitable production technologies for increased yields under various conditions.
Background
This species grouping is ideal for aquaculture on a global scale by virtue of the following attributes: (a) worldwide distribution and high market demand, (b) herbivorous and detrital feeding habits (low trophic level), (c) wide salinity tolerance, and (d) existing international interest in their cultivation.
Present culture and future potential in developing countries
The culture of mullets is of interest to most developing countries. About eight to ten species are presently either cultured or are the subject of applied research for culture. Of these Mugil cephalus is the most widely distributed and cultured species.
Mullets are cultivated in both brackish and freshwater ponds, mostly in association with other fish species. Culture systems are based on enchancement of natural food in ponds and/or provision of supplementary feeds. The best available estimate of current aquaculture production is probably not more than 50 000 metric tons.
The potential for increased production of mullets can be considerable. Projection of future, or potential production in quantitative terms, is difficult but a ten-fold increase is perhaps possible.
Technical constraints to increased production
(a) Seed: without exception, culture of mullets is predicated on natural seed supplied. The unpredictable nature of this supply, coupled with high mortality in collection, is further aggravated by the tendency of fry of several mullet species, which are difficult to differentiate, to school together.
Research aimed at the development of standard methods for the breeding of captive stocks and mass production of seed is considered the most critical input for expanding production of mullets. Standardized breeding methods are presently available for one species, M. cephalus, and this needs to be adapted to other species while larval survival needs further research.
(b) Health: disease problems are not considered a major constraint to production in the near term although health problems can be expected to arise as more intensive systems are developed. A more urgent target for immediate research is resolving problems of fry mortality during transport and in nursery ponds. This problem should be attacked simultaneously with controlled seed production.
(c) Feeds and natural food: though their food habits are known and have been used to develop profitable extensive culture systems, little is known about the nutritive requirements of mullets. Though not constituting a major constraint to production in current production systems, it is a constraint to the development of intensive systems. Research in this field is assigned a secondary priority in relation to research on seed production.
(d) Genetics: genetic selection will become possible when methods for controlled breeding and seed production are developed. Although not considered a medium-term priority, genetic engineering should be a major objective of applied research in the long term.
Milkfish, a marine/estuarine (euryhaline) herbivorous species which occurs from the coast of Eastern Africa across the Pacific to the coast of Latin America, is mostly cultivated in the Indo-Pacific region. Total annual production is estimated at 0.3 million tons. The potential increase in production may conceivably be tripled by application of known technologies. Since the source of fish seeds is from the wild, increasing demands for fish seeds will create a problem for the milkfish culture industry.
Priority research areas are in the standardization of breeding techniques to satisfy demand for fish seeds, including fish health studies to maximize survival of juveniles, while ensuring the maintenance and improvement of culture systems which provide adequate food and feed supplies and compatible species combinations in integrated cultures.
Greatly increased production is possible in current pond operations provided that adequate seeds are available. Extending the culture practices to new localities within the range of distribution of milkfish can very appreciably enlarge production because of its adaptability even to fresh waters as a phytoplankton feeder.
Seed production
Source of seed supply at present from the wild; highly seasonal; shortages of supply due to high mortalities and more intensive culture systems.
Production of fish seeds under controlled conditions will greatly help solve the problem of providing the fish seeds demanded by more intensified milkfish culture. Breeding methods require more in-depth studies together with broodstock development. This is of very high priority.
Feeds and natural food
Research on the growing of natural food and feed development is of high priority. Intensive culture systems of milkfish in ponds, cages and pens will require research in fertilization of ponds including supplementary feeding, and artificial feeding in pens and cages.
The research on breeding and broodstock of milkfish will also demand feed and food research for the larvae stocks and the broodstock.
Health
This is not a major problem at present. However, hatchery and broodstock development and more intensive culture systems will require preventive measures for health protection.
Genetics
Reseach in genetics cannot be done until after the breeding technology is better developed.
Culture systems and their management
Pond culture is still basically extensive to semi-intensive with use of fertilizers (organic and chemical). There is very little pond engineering and adequate pond management being undertaken. Pen culture is also done in lakes with or without supplementary feeds. Production per unit area in culture systems, particularly in ponds, can be considerably increased through research in pond management, better fertilization techniques, stock density and manipulation, pond ecology, feeding, and polyculture.
This research area is considered high priority, especially on a regional and national level.
Integration of other crops
Integration of agricultural farming (livestock) with milkfish culture is highly desirable in view of possible shortages of standard organic fertilizers and the increasing costs of said materials due to competition from other agricultural crop farming.
Post-harvest studies
Post-harvest studies are needed to help solve marketing problems such as:
This group includes several species, some of which are being cultured on a large scale, some that are being raised only on a limited scale but have great potential for expansion and others that are being cultured at present only on an experimental scale. The following are the species of importance, most of which are freshwater species:
Clarias batrachus
C. macrocephalus
C. lazera
Heteropneustes fossilis
Pangasius sutchi
P. pangasius
Chrysichthys nigrodigitatus
Pimelodus clarias
Most of these species are omnivorous in their feeding habits, grow well in captivity and can be bred relatively easily. Consumer acceptance varies with species and region. Regardless of this, catfishes as a group has considerable potential for much wider use in culture in developing countries.
In areas where catfish culture in ponds is intensive, disease has been a problem of major significance. This is often related to pond management problems created, among others, by the type of feeds and feeding procedures, stock densities, water management, etc. The development of suitable feeds and pond management measures will, therefore, be of special importance. For species that are cultivated experimentally and only to a limited extent, development of methods for mass production of seed, feed development and culture management, are high priority areas for investigation. For species that are used in cage culture, the various aspects of culture management assume special importance. The maximum research efforts would be required in respect of the species for which the technology is at an early stage of development, as for example Pimelodus clarias. While genetic studies can certainly contribute to improvement of catfish culture, these will have to wait till the direction of such studies can be determined on the basic experience acquired in production studies.
Species
This broad grouping of shellfish includes oysters, mussles, clams, scallops, abalone and other gastropods. Oysters and mussels are widely grown by aquaculture whereas culture of most of the other species is just developing.
Oysters used in the tropics include various species of the genus Crassostrea. In the temperate zones oysters of the genus Ostrea are also grown by aquaculture.
Mussels of the genera Mytilus, and Perna occur widely in the tropics supplemented in the temperate zone of South America by the genus Aulacomya.
Significance in developing countries
Both oysters and mussels are widely used as staple foods in areas where natural populations occur. Simple forms of aquaculture such as collecting seed from natural reproduction and planting it in suitable areas are used in some place.
There are excellent opportunities for expanding oyster and mussel production by applying proven systems which are used elsewhere, with modifications to suit local environments and species. The production and consumption of bivalves in tropical countries can be greatly increased through the application of established methods used elsewhere.
The recent successes with tropical oyster and mussel culture indicate that it will be possible, through site specific investigation of known research principles, to provide very substantial production from estuarine and protected coastal areas. Production of mussels reaching 30 tons per hectare has been achieved in tropical areas. Molluscs filter phytoplankton or detritus directly from the water, so there is no feed cost involved in their culture. There is also potential for combining the culture of oysters, mussels, seaweeds and estuarine fishes in profitable low-cost enterprises for coastal communities.
Although several other species of molluscs have some potential for aquaculture, none have as wide application in the developing countries at present as oysters and mussels.
Constraints to aquaculture
Health
Periodic mass mortalities often of unknown causes, occur in most areas where oysters or mussels are grown. Therefore much research is needed to determine the cause of such mortalities and to develop preventative procedures or controls. It is likely that this will require a continuing programme for five to ten years.
Although research in the temperate zone has identified some causative factors, little if any work has been done to understand the causes of mortality in the tropics.
Another health problem, related more to humans than to the molluscs, is paralytic shellfish poisoning. Molluscs which ingest toxic dynoflagellates without harm can cause illness when eaten by humans. The factors causing blooms of these “red tide” organisms are not well understood, especially in the tropics. Therefore, research is needed to provide a basis for monitoring toxicity in the shellfish and controlling harvesting to ensure safety to the consumers.
Seed
Natural reproduction of oysters and mussels, especially in the tropics provides a ready source of seed. However, some adaptive research will be needed to modify seed collection methods used elsewhere to local environments and populations. Although important, this is not a difficult, expensive or long-term form of research.
Genetics
In most developing countries seed oysters and mussels can be obtained from natural reproduction so there is little opportunity for selection breeding or genetic improvement. However, in some developed countries where hatcheries have been established, genetic improvement of stocks has high potential. The results of this research may provide improved seed for use in developing countries.
Species
Two major groups of crustaceans, marine shrimp largely of the genus Penaeus and freshwater prawns of the genus Macrobrachium have potential for culture in the tropics.
Significance in developing countries
The culture of marine shrimp and freshwater prawns in low technology pond systems is already established in developing countries of tropical Latin America and Asia. Although the product is often too valuable to be consumed by the producer, it finds a ready market in urban areas within the country or in export markets, providing substantial income to the producer.
In other cases, large commercial-scale shrimp or prawn farms provide employment opportunities for local workers.
Constraints to aquaculture
Reliable methods are available for maturing freshwater prawns in captivity, rearing the larvae and growing juveniles to market size. The major constraint is the development of reliable procedures to maximize production in pond culture systems.
Marine shrimp can also be grown in ponds by proven methods, however, procedures for maturing adults of most species in captivity have not been perfected. As a result seed is unavailable or too expensive. Successful hatcheries have been established for Peneaus japonicus, P. stylirostris, P. vannamei, P. monodon, P. merguiensis, P. indicus but much research is needed to provide a sound scientific basis for developing hatcheries for other species.
Pelleted feeds for both marine shrimp and freshwater prawns are available from commercial sources but this usually requires importing and substantial freight costs. Low cost feeds using local ingredients are needed to develop economical prawn or shrimp culture in most developing countries.
Health problems are more critical in the culture of marine shrimp than freshwater prawns but continuing research will be needed to develop reliable control methods as farming of both groups develops.
The opportunity for genetic improvement of stocks will become available when reliable hatcheries are established.
Each discussion of species has described some of its needs in production systems development. This attempts to suggest a general approach to the necessary systems research.
It would appear that much can be learned quickly through an approach involving the careful study of existing full-scale projects in conjunction with work in research stations, pilot plant operations, theoretical analysis and the use of existing production operations modified to demonstrate improved concepts. Adaptive research on all scales based on modification of successful projects will also aid in technology transfer.
The primary objective of this approach to culture systems research is to provide to the potential fish farmer the available information he needs to make proper investment decisions as soon as possible and to minimize his investment in deriving the information and in developing his project. Further, this research should provide to the fish farmer the understanding he needs to operate and improve his facilities once constructed.
The effective distribution of this information is necessary to make best use of this research.
