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State of World Aquaculture and its Future Role

K. Tiews
C. Nash

Panel Members

T.V.R. Pillay:Overview of aquaculture development during the last ten years
S. Tal:New trends in aquaculture development
G.M. Gerhardsen:The role of aquaculture in integrated rural development
P. Briggs/J.B. Glude:Vertically-integrated aquaculture industries
J.E. Bardach:The future of aquaculture - Potentials and constraints
K. Tiews:Organization of aquaculture as a constraint on future development
Relevant Documents:FIR:AQ/Conf/76/R.4, R.10, R.13, R.16, R.19, R.21, R.25, R.30, R.33, R.35, R.36, R.38, R.39,
/E.2, E.4, E.8, E.18, E.20, E.22, E.26, E.51, E.55, E.71, E.75, E.77, E.82

State of aquaculture

The session attempted an overview of the progress of aquaculture during the last decade, since the last world meeting on fish culture (FAO World Symposium on Warm-Water Pond Fish Culture, Rome, Italy, 18–25 May 1966). Over a fourfold increase in the attendance of the Conference was considered indicative of the increased interest in aquaculture in most countries of the world. Increase in production, which is a better measure of the progress of aquaculture, continues to be difficult to assess because of the lack of detailed and reliable statistics. Based on available data collected from government and other sources, production in 1975 has been estimated to be over 6 million tons as against the 1973 estimate of 5 million tons. Although the previous as well as the present estimates cannot claim any high degree of accuracy, the available information clearly shows that in almost all the countries there has been an increase in total production. The most notable fact is that appreciable increases have occurred in countries where sufficient importance has been given to the industry in national agricultural and industrial development programmes. This has led to increased government spending, enhanced private capital investment and better support services. Factors that have contributed to such developments appear to be the increasing cost of fishing, the impending changes in the Law of the Sea and the need to relocate excess fishermen or find alternate or additional employment for farmers or fishermen. The role of aquaculture in integrated rural development is also now better understood in many countries. As one of the key factors for future aquaculture development was recognized to be the priority that governments and the industry accorded to this sector, it was suggested that the Conference should adopt a Declaration to serve as a policy instrument reflecting the determination of governments, and the world community to accord aquaculture an appropriate level of priority.

New trends

General inflation and particularly increases in feed, labour and other input costs, has adversely affected some aquaculture industries in recent years. This has had the effect of eliminating the marginal or inefficient producer in some countries and bringing about a general trend toward intensive farming to achieve higher production per unit area and higher profit on investment. This trend is worldwide, but the conditions in many developing countries still permit the adoption of extensive farming techniques and in many cases such techniques continue to be the most economic ones.

Clearcut classification into “extensive” and “intensive” aquaculture may not be quite valid because of the many intermediate and overlapping classes that occur. However, developed countries generally adopt intensive methods of aquaculture because of: (a) the limited land and water resources available, (b) high cost of labour, and (c) the high-valued species occupying higher trophic levels that they are required to farm. The new technologies developed for the production of salmon, trout, yellowtail and shrimp are examples. However, even in less developed countries intensive culture systems that yield very high production rates have been developed. The polyculture systems developed in Israel and India, catfish culture in Thailand and cage culture in the Mekong river system are examples.

Technological advances during the last decade are largely based on the scientific understanding of traditional practices and improvements brought about in these practices through research. Examples are cage and pen culture, polyculture of fish, waste recycling through aquaculture, etc.

Role of aquaculture in rural development

As mentioned earlier, one of the recent trends in aquaculture development has been the readiness of planners and administrators to accept it as a part of integrated rural development. On a global scale, aquaculture production when properly planned and managed, can contribute very substantially to increased food supplies in the rural areas. By offering employment opportunities and improving the nutrition and the standard and quality of life of the rural poor, and particularly by improving their productivity, it is to be expected that their contribution to the national economy can be substantially enhanced, leading eventually to economic well-being and self-sustained growth.

Demonstration of viability and, in a narrow sense, profitability under different rural conditions is often demanded as a requirement for inclusion of aquaculture in rural development projects. While the economic profitability is a prime concern, it is also necessary to take into account the social value of the projects. For the assessment of the socio-economic importance the “added value” produced and that portion of the added value which is retained in rural areas can be used. Much will depend on how this value is defined, but physical productivity or efficiency, wages, rates of interest, cost of capital equipment as well as price of aquaculture products, will be important factors to be taken into account in assessing viability. Although it is not correct to generalize, it can be said that in a majority of developing countries there will be a marked preference for small-scale labour-intensive forms of aquaculture for integration in rural development programmes. This does not in any way rule out the possibility of large-scale enterprises in rural areas.

The success of small-scale rural aquaculture would to a large extent depend on the support services that are made available. The small farmer would greatly benefit from a “package” of technical assistance, provision of inputs and institutional credit on reasonable terms. As in the case of rural agriculture, rural aquaculture development requires a major effort to develop innovative approaches to project design and implementation.

Vertically-integrated aquaculture industries

Large-scale aquaculture industries, particularly in developed countries, are often associated with vertical integration. Vertical integration has many advantages, including the opportunity to spread profit or loss over the different sectors of production, processing, distribution or sales. It also provides the incentive to maintain quality because profit depends on the acceptance by the consumer to whom the product has to be sold. However, a survey of aquaculture industries in the United States, as an example, shows that only a few of them, such as some oyster, crayfish and baitfish farming industries, are substantially integrated. Some of them, e.g. shrimp farming and salmon farming, are becoming, or planning to become, vertically integrated.

The discussions in the session clearly showed that vertical integration is not necessarily associated with the size of the enterprise. In fact there are many instances of small-scale operations, including even subsistence farming, that are by definition vertically integrated. On the other hand, many large-scale operations such as catfish farming and trout farming in the United States are not integrated as most growers buy their requirements of feeds or seed and sell the produce through established marketing channels. While vertical integration has admittedly many advantages, it is neither mandatory for efficient management nor characteristic of the standard of economic development of a country.

Organization of aquaculture

A good proportion of current fish production through aquaculture comes from socialist countries with planned economies where farming is done in state farms, communes and cooperative farms. In other countries production is largely in the private sector where small individual farmers dominate the scene. In recent years a number of small companies has entered the field and the recent trend toward diversification of industrial and agricultural production promises increased involvement of private companies and large investment of private capital. In aquaculture industries established and operated with financial profit as the main motive, a greater degree of vertical integration will be sought. Though a clearcut classification of patterns of preferred aquaculture for developing versus developed countries cannot be made, there is likely to be predominance of small-scale enterprises and subsistence level operations in developing countries even in the future. The opportunities for integration of aquaculture in rural development programmes are also found in the developing countries.

Research, training and other support services are crucial to the success of small - as well as large-scale aquaculture, but the need for extension services is much greater when the industry is dominated by small operators. Government support for multidisciplinary research, institutionalized practice-oriented training, production and distribution of inputs and provision of supervised credit are essential for the establishment and operation of commercial scale aquaculture.

The session recognized that there are a number of existing technologies that could be adopted with modifications where necessary, to achieve increased production. Research on some of the new systems and species has reached a stage when pilot-scale production projects are necessary to make further advances, including the refinement of technology. For such pilot-scale operations as well as large-scale commercial production programmes, necessary financial and institutional support are of prime importance. The World Bank Group, Regional Development Banks, FAO Bankers Group and the International Fund for Agricultural Development were suggested as suitable sources of financing for such projects in developing countries. The hope was expressed that financing agencies will adopt a progressive policy in supporting a new and emerging industry like aquaculture.

Future of aquaculture

The steady increase in world production through expansion in areas under culture and improvements in technology enabling intensification of culture, tends to show that aquaculture will come to play a much greater role in food production in the future. Even by the expanded use of existing technology it is expected that a doubling of world production will occur during the next decade. A five- to ten-fold increase by the turn of the century also appears feasible if the necessary scientific, financial and organizational support become available.

Possibilities for aquaculture development are not restricted to food production. Pearl culture has expanded to countries outside Japan; culture of colloid-producing algae is gaining importance; baitfish culture, which so far supported sport fisheries only, now shows possibilities of being of importance also in commercial fishing as, for example, tuna fishing. Ornamental fish culture is an expanding industry of considerable economic significance. Large-scale rearing of crocodiles and other animals for industrial products is also becoming feasible.

The best use of ecological opportunities can be expected to play a major role in achieving the potential for expansion of aquaculture. This may occur in many ways, such as by the use of heated waste water, domestic and municipal effluents, animal and agricultural wastes. Artificial upwelling to raise the nutrient-rich subthermoclinal sea water for aquaculture in shore ponds, floating enclosures or other flow-through systems, are other possible developments of the future, although the engineering and economic constraints appear formidable at present.

Expansion of aquaculture will undoubtedly involve the use of additional areas, and coastal swamps and mangroves are likely to figure prominently as potential sites. The need for closer critical study of the ecological impacts of converting such areas into aquafarms cannot be over-emphasized.

“Sea ranching”, “sea farming” or “culture-based fisheries” have in recent years proved their technical and economic viability in respect of anadromous species like the salmons. Progress has been made in ranching also less migratory species like shrimps. The expansion of this type of farming holds considerable promise for the future. However, such development is restricted to the temperate regions of the world and there is need to make a thorough search for suitable species for the tropical areas.

The importance of well designed pilot projects for different types of aquaculture in different parts of the world was further emphasized by the session in discussing the potentials and constraints of aquaculture development. In this connexion special mention was made of the need for integrated development assistance and cooperation between funding agencies in supporting research and development projects.


(Section 1)
Pond Culture of Finfish

J.W. Avault
R.O. Smitherman

Panel Members

J.W. Avault:An overview of fish culture systems for large-scale production
Y.A. Tang:Site selection, design and construction of fish ponds
H. Chaudhuri:Seed production and distribution
E.M. Donaldson:Technological improvements in controlled reproduction of fish
V.R.P. Sinha:Fish farm management
S. Sarig:Fish diseases and their control in pond culture
H.R. Rabanal:Economics of pond fish culture
Relevant Documents:FIR:AQ/Conf/76/R.2, R.10, R.15, R.19, R.22, R.28, R.30, R.32,
/E.1, E.2, E.5, E.6, E.8, E.9, E.13, E.14, E.15, E.16, E.20, E.30, E.34, E.39, E.43, E.46, E.47, E.51, E.54, E.63, E.64, E.65, E.66, E.68, E.70, E.76, E.77, E.78, E.79, E.80, E.81

State of finfish culture

Finfish culture constitutes the most important sector of the aquaculture industry at present and accounts for about 75 percent of current world production. Major increases in future finfish production are expected to occur through expansion of area under culture and by the utilization of new and improved technology. One of the constraints on expansion of aquaculture is the conflict in land and water use that exists in many countries, including developing countries that are in great need of increasing animal protein production. There are, however, extensive areas of marginal lands where conflicts with traditional uses such as agriculture are minimal. The mangrove swamps in tropical countries are of special importance in this respect, but there is widespread concern on the ecological effects of large-scale reclamation of such swamps. Critical studies are required to establish procedures for preventing adverse environmental consequences and provide adequate nursery grounds for larval and juvenile fish and shrimps. Polyculture, intensification of current culture practices and adoption of rice-cum-fish culture are possible ways in which production can be increased. Production of up to 10 tons/ha/year has been achieved through polyculture in India and Israel. Intensive culture involving high density stocking, feeding and aeration has produced up to 25 tons/ha/year in Israel. For the wider application of improved techniques, the organization of suitable extension services is of crucial importance. The integration of agriculture, livestock and poultry raising with aquaculture has been demonstrated to be capable of maximizing overall production and income to the farmer.

Adoption or expansion of ricefield fish culture is impeded by modern intensive agriculture practices involving the use of pesticides and other toxic chemicals. However, the current researches at the International Rice Research Institute in the Philippines on fast-maturing varieties, floating rice, development of pest-resistant strains and soil injection of pesticides instead of spraying as practised now, offer hopes of solving some of the problems.

Site selection and design of fish farms

Experience in different parts of the world clearly highlights the crucial importance of site selection and farm design in pond culture of finfish. Site selection has to be based on adequate data on the hydrometeorology of the region, such as rainfall, solar radiation and evaporation and hydrology such as tidal range, watershed and drainage, water table fluctuations and water quality. Knowledge of the chemical and physical properties of the soil, basic engineering, fish farm management and economics of operations have to be brought to bear both in site selection and farm design. Since the main capital investment in fish culture projects consists of fish farm construction and a significant part of operating costs relates to farm maintenance, proper siting and construction assume special importance.

Coastal fish ponds filled by tidal action are estimated to comprise about 18 percent of existing fish farms. The rest are inland ponds filled by run-off, diversion or seepage. The selection of sites for a tidal fish farm is limited by land elevation and tidal range characteristics. The development of inexpensive systems of supplemental water supply could greatly increase the availability of suitable sites. Another major problem faced is the acidity of coastal swamp soils, caused by the accumulation of iron and sulphate salts. If a system of low-cost interceptor drains can be developed to leach out such salts, it may be possible to improve the soil in a relatively short period of time. The recent trend toward integration of fish farming with water resource development schemes could result in the enhanced availability of sites for inland ponds fed by diverted or seepage water.

Controlled breeding and seed production

In spite of the progress made in recent years in the controlled reproduction of some of the cultivated fishes, seed production continues to be based on the collection of wild fry in many countries. Inadequate supply of fish pituitary gland is one of the constraints on wider application of induced breeding techniques. The need for establishment of pituitary banks and the search for new sources of pituitary material, such as tuna which may be more widely available from canneries, was highlighted in the discussions on this subject. It is also important to have adequate numbers of brood fish in prime condition for breeding purposes and to develop the necessary expertise for improving hatchery operations so as to increase survival of hatchlings.

While the focus at the present time may be directed toward the application of the first generation techniques in controlled reproduction already developed, there are five areas of research that need special attention in the future, viz. (a) acceleration of gonad development, (b) induction of spawning, (c) sex reversal, (d) sterilization, and (e) preservation of gametes. It can be said in general that the best approach to acceleration of gonadal maturation in fish at present is by means of environmental control. The increased use of hormones for this purpose will depend upon the development of slow release capsules or pellets which can be implanted in fish. The implantation of cholesterol pellets containing gonadotropin at regular intervals has been tried with encouraging results. Techniques for induction of spawning consist of the provision of an appropriate environment to induce natural spawning or the injection of natural or synthetic biochemicals which (i) stimulate the release of endogenous gonadotropin from the pituitary gland, (ii) contain exogenous mammalian or piscine gonadotropin, or (iii) stimulate the natural steroids or other compounds normally induced by gonadotropin in the gonad. To date most of the work has involved the injection of exogenous mammalian or fish gonadotropin. Active research is required to isolate and synthesize the fish gonadotropin-releasing hormone or test analogues of LH-RH which may be more potent in fish. Successful sex reversal can have many applications in fish husbandry and is an urgent need in tilapia culture. It was reported that fry of Tilapia mossambica fed methyltestosterone at a dose of 30 mg/kg in the diet for four weeks produced 95–98 percent males. The effect of such treatment on the acceptability of the fish for human consumption needs to be investigated. So far no satisfactory means of sterilization seems to have been found. Some progress has been achieved in the preservation of sperms in a number of species. Up to 45 percent fertilization has been achieved in pink salmon (Oncorhynchus gorbuscha) using milt stored for one year in liquid nitrogen.

While efficient techniques of controlled reproduction and hatchery rearing are of considerable importance for aquafarming, the industry will not prosper without appropriate organization of the production and distribution of seed. Seed production and distribution can become a specialized and separate industry as it is already becoming in some countries.


While future development of aquaculture will, to a large extent, depend on proof of its economic efficiency, essential relevant data continue to be scarce. There is an urgent need to collect and compile economic data to enable enhanced investments in fish culture and to facilitate insurance and risk management of enterprises. Capital investment in fish culture is rather high and therefore there is a tendency to economize, which leads to inefficient operation and loss of crops. The profitability of fish culture has been demonstrated in many areas under different conditions; however, in recent years the costs of inputs such as feeds, fertilizers and seed have been rising rapidly without commensurate increases in the price of fish produced. The adoption of intensive culture techniques has resulted in increased yields but this also involves increased production costs. For example, intensive milkfish culture involves high density stocking and due to increasing demand for fry and reduced availability, the cost has risen 1 000 percent in ten years. This situation has led to a trend toward the culture of high-valued species for export even in countries that need to produce cheap fish to feed the local people. Increasing yields, reducing production costs and ensuring equitable price for the products are essential steps for improving the profitability of fish culture.

Fish farm management and disease control

The crucial importance of efficient management for the success of fish culture was specially emphasized throughout the discussions. The adoption of more intensive methods of culture generally involves greater attention to management. The chances of diseases and mass mortalities due to various stress factors become much greater. Parasitic infestations predominate in warm waters and bacterial and viral diseases in coldwater fish stock. Considerable advances have been made in recent years in diagnosis and methods of control and therapy. Wider adoption of these could greatly reduce future losses. Much more work has to be done before immunization of fish against diseases can be widely utilized. The development of disease-resistant strains for culture will have special significance in fish culture programmes.

In summing up the discussions in this session the following specific actions were recommended:

  1. Studies should be undertaken on environmental and physical characteristics relating to aquaculture such as temperature, rainfall, soil type, availability of water, electrical energy, land use, manpower, commodities and feedstuffs.

  2. Suitable species for culture should be evaluated with regard to the physical and environmental requirements for fast growth.

  3. Production functions relating physical and environmental levels to production costs should be developed for each species.

  4. The above data should be combined to produce maps depicting locations suitable for culturing specific species, as well as their associated production costs and economic opportunities.

  5. Sources of pituitary material in fishes such as tunas should be investigated.

  6. Depositories for sperm and pituitary material should be considered on regional and international bases.

  7. Sex reversal and other methods of sex control should be further investigated.

  8. Concerted effort should be continued on the reproduction of species such as the milkfish.

  9. Improved systems should be established for the collection and distribution of wild fry.

  10. Strains of fish which are resistant to specific fish diseases should be developed through selective breeding.

(Section 2)
Culture of Crustaceans

H. Kurata
P.A. Sandifer

Panel Members

R.A. Neal:The present state of shrimp farming and its problems and prospects
H. Kurata:Shrimp farming in Japan
J. Perrot:Breeding of shrimps and production of seed
Y. Hirasawa:Economics of shrimp and prawn farming
S.W. Ling:Macrobrachium farming
R.A. Shleser:Lobster and crab culture techniques
Relevant Documents:FIR:AQ/Conf/76/R.12, R.17, R.18, R.27, R.29,
/E.3, E.11, E.16, E.22, E.23, E.33, E.36, E.38, E.40, E.42, E.44, E.45, E.49, E.57, E.77

State of crustacean farming

For various reasons there has been an upsurge of interest in the farming of crustaceans, particularly shrimps and prawns, during the last decade. To some extent the increased demand for shrimps and the fall in capture fishery production resulting in high cost of the product account for this. Although some forms of traditional shrimp farming have existed in Asia for many years, it was Japan's success in propagation of Penaeus japonicus that attracted worldwide interest in this type of farming. Considerable experimental work is underway in many countries, but it must be admitted that, in general, crustacean farming is in its infancy and production is still at a low level. However, the technological advances in recent years indicate that the prospects for future development are bright.

Much of the emphasis in recent work on shrimps and prawns has been on controlled reproduction of the animals and mass rearing of larvae. Appreciable progress has been achieved in these fields, although further improvements are needed. But this cannot be said of the phase that follows, namely profitable grow-out from juveniles to market size. Only in areas where the price of products is high, as for kuruma shrimp in Japan, or where labour and food costs are low, has it been possible to achieve economic production. Data supporting the viability of “culture-based fisheries” or sea ranching of shrimps in Japan are now becoming available. Since 1974 a total of 150–200 million juveniles has been released into the Inland Sea and has apparently contributed to increased capture fishery landings. The recovery rate is estimated to be about 5.7 percent and it is hoped to raise it to 10 percent. This and the results of polyculture of Macrobrachium with fish give hopes for initiating large-scale production programmes in the near future. Experience in the United States indicates the possibility of what is termed “bay farming” of shrimps under semi-controlled conditions in natural bays.

Shrimp farming

A major breakthrough in recent years has been the maturation and spawning of several species of penaeid shrimps. Several species, such as Penaeus merguensis, P. semisulcatus, P. japonicus, P. aztecus and P. monodon, have been matured and spawned under controlled conditions. Some of these, notably P. merguensis, matured and spawned under natural conditions. P. japonicus spawned by carefully manipulating environmental factors (mainly temperature and photoperiod), while most matured only after ablation of one eyestalk. Adoption of this technique may eventually serve to solve the problems associated with dependence on the reproductive cycle of wild shrimp. It often proves difficult and expensive to obtain enough mature shrimps from the wild. This operation also restricts the period of availability of larvae and juveniles for farming.

Several improvements have been effected in the methods of larval rearing of shrimps and prawns. Some of these methods involve a high degree of environmental control and the use of monospecific diatom cultures and compounded feeds. Such improvements have resulted in high survival rates.

In discussions on larval culture, special attention was devoted to the supply of the larval food Artemia. There are over 60 strains of Artemia salina worldwide and many unexploited resources exist. It was suggested that FAO should assist in the collection of information on such resources. Further studies on the biology and ecology of Artemia should be undertaken to provide the basis for more efficient production and exploitation in natural or artificial environments. There is a need for developing more efficient and cost-effective procedures for hatching and utilization of Artemia cysts in order to conserve available supplies.

Work is now underway in a number of countries to identify suitable substitutes for Artemia and already some success has been achieved. Gammarus, Brachionus and chironomids have been tried with considerable success. Further efforts on these lines should be encouraged.

In the rearing of shrimps for the market, the recent trend has been toward intensive monoculture. In some of the Asian countries increased yield per unit area has been achieved in brackishwater ponds through the improvement of traditional practices. P. monodon shows considerable promise in Asia, where satisfactory production has been obtained in pond culture using wild juveniles. With the development of easy methods of maturation and spawning, P. merguensis culture is likely to intensify in most countries of Southeast Asia.

Attempts are being made to introduce more intensive shrimp culture techniques in Japan and the United States. A flowing-water system that produces 20–30 tons/ha annually and 4 tons/man-year has been developed. Closed cycle growing units are being tried in the U.S.A. In both cases the main constraint is the cost involved.

Significant progress has been achieved in the development of compounded diets for shrimps which give good results in terms of growth response and cost effectiveness. However, overall there appears to be a need to devote greater attention to production of natural food for shrimps in ponds and the adoption of combination feeding regimes, utilizing ecologically-balanced systems with supplemental feeding. Attempts along these lines are underway in some centres in Asia and Latin America. In considering nutrition and feeding, it was pointed out that the possible differences between various species of shrimps have to be taken into account. There is some indication of significant differences in protein requirements between cultivated shrimps. This may apply also to ecological requirements. A plea was therefore made to return to the study of the basic biology of shrimps after years of concentration on culture techniques.

Experience in “sea farming” or development of “culture-based fishery” for shrimps in the Inland Sea area of Japan shows that the major factor restricting the survival of juveniles released in the sea is intensive predation by certain species of fish. To overcome this “artificial tide lands” have been designed with a view to controlling the environmental conditions and preventing predation of the relatively sedentary juveniles.

Detailed economic assessments of shrimp culture in different situations are not yet available, but it is clear that a major cost of production in intensive systems is the cost of feed. In view of its great significance to the success of operations, there is a need to concentrate greater research effort on producing less expensive feed and improving feed conversion efficiency. As already pointed out, the profitability of shrimp farming in many areas of Japan is primarily due to the high price of live cultured shrimps in the country. This has enabled the culturists to adopt intensive culture methods involving heavy capital investment and high production costs.

Macrobrachium farming

The artificial propagation of the freshwater prawn Macrobrachium rosenbergii in Malaysia in 1962 led to worldwide interest in the culture of this large prawn and research to develop an economically-viable culture system is now underway in several countries. At present there are over 20 organizations engaged in studies of Macrobrachium in the United States alone. Considerable improvement in the larval rearing techniques were achieved in Hawaii (U.S.A.) and this has been followed by the development of a small number of commercial farms. In Southeast Asia, particularly in Thailand, small-scale private hatcheries and grow-out operations are increasing. In developed countries the emphasis is on intensive culture systems and one of the major problems faced in their development is the high cost of feed. Formula feeds have been used for the culture of M. rosenbergii in larval and juvenile phases, but success with larvae has been limited.

The possibilities of culturing about a dozen species of Macrobrachium have been tested, but to date the most widely used species is M. rosenbergii. M. lanchesteri and M. malcolmsonii have also shown marked farming potential.

Lobsters and crabs

Culture of the American lobster Homarus has received more concerted attention in recent years. It is possible to breed the species routinely in captivity. The time from mating to hatching of eggs has been reduced to eight months in the laboratory compared to two years in the wild. The technique of larval culture has been considerably improved and 70–80 percent survival obtained. Closed-system rearing with automated feeding has given very encouraging results. Culture of post-larvae through four larval stages has been achieved in ten days at 22°C. Due to their cannibalistic habits individual holding arrangements have been adopted for the culture of post-larvae. Different types of individual holding systems have been tried, such as the stacked tank arrangement with water supply from below in Bodega Bay and the circular system with water provided from above as in San Diego. Experience has shown that by warming the water to 22°C the time to produce a marketable 450-g lobster can be reduced from 7–9 years in the sea to approximately 2 years. Thus the key to commercial culture of the American lobster may be the provision of adequate quantities of warm water at low cost. Various means of providing low-cost heat are being evaluated, including closed systems, partial re-use of water coupled with waste treatment and utilization of thermal effluents from power plants. Progress has been made in defining the protein and fatty acid requirements of H. americanus. Work is underway to formulate low-cost diets with improved growth characteristics, but further work on feed composition and stability is clearly required.

Hybrids of H. americanus and the European lobster H. gammarus have been obtained and the characteristics of the progeny are now being evaluated. Selective breeding for eyeless lobsters which grow approximately 35 percent faster than normal lobsters has been reported. This seems to indicate that a 500-g animal can be produced in 12–15 months at 22°C. If enough supply of heated water at a reasonable cost is available, the production of market size Homarus at a competitive cost may become possible. It therefore appears that experimental work has reached a stage when pilot-scale operations are necessary to evaluate economic viability.

Although most of the recent work on lobster culture has been related to the American lobster, some investigations on the possibility of culturing spiny lobsters have also been undertaken in the United States, Australia and the Bahamas. Since spiny lobsters are not cannibalistic, rearing them should be easier. Post-larvae and juveniles caught from lagoons have been used for experimental culture in the Bahamas and Tahiti. It is reported that they could be grown to market size of about 500 g in about one year in Tahiti. There is much more work to be done to enable their reproduction in captivity and the culture of larvae under controlled conditions.

But for small-scale culture using wild juveniles in some Southeast Asian countries, there appears to have been only very limited progress in crab culture. The cannibalistic nature of adults is one of the major problems and economic means of preventing this or achieving minimum survival rates have yet to be developed. A number of research groups are at present working on the reproduction and larval culture of different species.

(Section 3)
Culture of Molluscs

P. Korringa
K. Mackay

Panel Members

J.B. Glude:Oyster farming
A.M. Figueras:Mussel farming
S. Mizumoto:Pearl oyster farming
P. Korringa:Economics of mussel farming
K. Chew:Potentials for the expansion of mussel farming
D.A. Hunt:Depuration of molluscs
Relevant Documents:FIR:AQ/Conf/76/R.3, R.7, R.11, R.13, R.16, R.19, R.34,
/E.7, E.28, E.37, E.52, E.58, E.69

Present state of mollusc culture

Molluscs form an important group of cultivated organisms and account for over 1 million tons of aquaculture production at present. They offer the best immediate means of developing marine farming. Being efficient converters of primary production, they have a number of advantages over many of the other cultivated species and generally production costs are relatively less. While most species are cultured for human food, some are used as animal feed, as, for example, mussels in Thailand. The culture of oysters and other molluscs for pearl production, which originated in Japan, has spread to other countries like China and Australia. Since 1966, when pearl production reached peak levels, the industry has declined considerably. This is ascribed to the mass production techniques adopted and consequent deterioration of pearl quality. Pearl culture has also been adversely affected by aquatic pollution causing high mortality of pearl oysters and deterioration of pearl quality.

Oysters and mussels are the most important molluscs now farmed on a large scale. Clams, cockles, abalone and scallops are cultivated in some countries. Even though environmental pollution and other problems have affected oyster production in certain areas, the total world production is definitely on the increase. All the standard methods evolved during the years continue to be employed, but off-bottom culture is being adopted in more areas than before. The floating longline method makes it possible to utilize less-protected areas for oyster and mussel production. The longlines offer less resistance to waves and wind and are less exposed to predatory fish. The capital cost is not higher than for rafts, but longlines allow more flexibility. There is need for greater engineering inputs in the design and construction of mollusc-growing facilities. Methods of increasing primary production, such as fertilization, have also to be adopted to obtain satisfactory yields.

As for the species used for culture, large-scale importation of Crassostrea gigas to Europe, especially France, has been undertaken to maintain oyster populations decimated by extensive mortalities of the local species. Four new species of mangrove oyster are being evaluated for culture, viz. Crassostrea rhizophorae in Cuba, C. tulipa in Sierra Leone, C. braziliana in Brazil and C. belcherii in Sabah.

The most significant trends in techniques are the use of hatcheries to produce seed, the beginnings of the genetic modification of stocks, and experiments to grow oysters to market size in a controlled environment. There are over 12 commercial oyster hatcheries in the United States at present. Strains of oysters resistant to the haplosporidian Minchinia nelsoni and strains with improved shell shape which results in a greater meat yield have been developed in Virginia (U.S.A.). The closed cycle culture of oysters in the University of Delaware (U.S.A.) was reported at the session.

Mussel farming

Interest in mussel farming is becoming more widespread and more species are now used for culture. The culture of Perna perna in Venezuela, Mytilus edulis aoteanus and P. canaliculus in New Zealand are new developments. Choromytilus choro and M. edulis chilensis, which are large species, have been shown to grow faster than M. edulis in Chile.

Five types of techniques are in use for mussel farming and they are adapted to the local hydrographical and socio-economic conditions. These include bottom culture as practised in the Netherlands, the so-called “bouchot” culture used on the Atlantic coast of France, raft culture in Spain, rack culture as practised in Italy and Yugoslavia and the system of submerged bamboo collectors adopted in the Philippines. All these systems have their advantages and disadvantages and the socio-economic conditions largely determine the system of farming adopted in any particular area.

A system like that in the Netherlands in which rather big ships equipped for fishing and planting of mussels are used requires enterprises of a large enough dimension to make farming remunerative, whereas the Philippines system makes operation on a small scale, for instance, family basis, possible.

Bottom culture, as practised in the Netherlands, has the advantage that it can be mechanized to a high degree, leading to a high production figure per man. A disadvantage is that crabs or starfish, both benthic predators, and the parasite Mytilicola intestinalis can more easily reach the mussels. A hanging culture, either making use of a raft in areas with great tidal range, or a rack where the tidal range is small, has the advantage that mussels can be grown where the water is rich enough in plankton but where the bottom deposits are too soft and muddy to allow the planting of mussels.

Disadvantages of hanging cultures are the limited possibilities for mechanization and the fouling of the mussel strings by ascidians, barnacles, hydroids, bryozoa and sponges.

A large increase in production has occurred in recent years in Spain. The increase of world production of mussels from 300 000 to 400 000 a year is mainly due to the growth of the Spanish industry. About 40 percent of the Spanish production goes to the fresh mussel market and the remainder is processed. The increased density of mussels achieved in raft culture causes problems because of accumulation of detritus in the vicinity of rafts. Investigation of this problem to find a suitable solution was suggested.

There are undoubtedly great possibilities for the introduction of mussel farming in countries where suitable sites are available. However, marketing and promotion of a mussel product may present problems in some countries where consumer acceptance is low. Production conditions are generally favourable in tropical areas where sea temperatures are high and labour costs relatively low. Although the basic technology of production is available there is need for improvement of the existing techniques and the development of new ones to solve the problems faced by the producers. It was suggested at the session that an international commission should be established under the auspices of FAO to review the problems and plan the necessary biological, technological, economic and regulatory or administrative studies involved.

Depuration of molluscs

The bacterial quality of the products is of special importance in mollusc farming, because in many countries they are consumed raw. This has led to the adoption of quality standards for products in some countries and water quality standards in others. Depuration or controlled purification of molluscs harvested from polluted waters is often enforced. Similar processing is sometimes adopted by the shellfish industry to freshen, condition or remove sand and extraneous materials prior to marketing.

The old technique of chlorine treatment is now being replaced by ultraviolet light or ozone treatment. Engineering design and operations of a depuration plant are predicated on the maintenance of favourable conditions for the shellfish during the depuration process. Bacteriological testing is the only method to determine whether depuration has actually occurred. Although a number of studies has been made, the maximum permissable number of viral particles which can be tolerated in shellfish harvested for depuration has not been established. Microbiological standards recommended or adopted in different countries vary. However, the need for selecting pollution-free waters for mollusc culture and depuration of products if waters are polluted, are generally accepted.

(Section 4)
Integration of Aquaculture with Agriculture and Animal Production

S.W. Ling
V. Gopalakrishnan

Panel Members

E. Woynarovich:Combination of aquaculture with animal husbandry
M.J. Vincke:Ricefield fish culture
K.G. Rajbanshi:Problems associated with combining aquaculture, agriculture and animal husbandry
S.W. Ling:Potentials for the expansion of aquaculture combined with agriculture and animal husbandry
Relevant Documents:FIR:AQ/Conf/76/R.6, R.10, R.19, R.22, R.35,
/E.17, E.20, E.29

It is expected that a good part of future aquaculture will be closely associated with integrated rural development in developing countries, where the improvement of the living conditions of rural populations has high national priority. Under-employment and low income of farmers are major problems in most of these countries and experience in Asia has clearly demonstrated that the combination of aquaculture with agriculture and/or animal husbandry can be a very effective means of solving these. The session therefore attempted an evaluation of the existing practices and discussed the possibilities of future expansion.

Combination of aquaculture with animal husbandry

The recycling of animal wastes through aquaculture is a widespread practice in China and fish farming is combined with production of other animals. Ducks and geese are raised in combination with fish in many East European countries and this practice has been introduced successfully on a pilot basis in some Asian and African countries. In fish-cum-duck farming the fertilization effect of the bird droppings enhances biological productivity and consequently fish production. Experience in Eastern Europe indicates that about 500 birds can be raised on one hectare of pond. They are estimated to yield about 3 tons of duck manure per year which, in turn, can contribute to an increased production of 120–180 kg of fish.

Average annual production rates of up to 3 500 kg/ha have been reported in this type of operation in Taiwan, Province of China. Experience in Hungary has shown that duck-cum-fish culture can be employed for improving sodic soils and making them suitable for agriculture.

In China pig manure is as important a product of piggeries as pork, ham and bacon. Also in other countries where fish-cum-pig farming has been tried it has proved to be an efficient means of waste disposal with considerable savings in fertilizer costs for fish production. Particular care has, however, to be taken to avoid pollution of pond water and contamination by infectious organisms. The maintenance of sanitary conditions is of special importance in this type of operation.

One of the problems faced in combining pig or duck raising with aquaculture is the difficulty in integrating the necessary expertise in fish and animal husbandry. The need for keeping these two in balance is important because over-concentration on one may work to the detriment of the other. For example, in fish-cum-duck farming it is possible to produce a ton of duck meat every 45–50 days and this can provide the farmer with a more frequent cash inflow than fish which he may be able to harvest only at less frequent intervals. This may lead to greater attention being paid to the ducks than to the fish. On the other hand, it is often the case that in such enterprises adequate hatchery and nursing facilities are provided only for fish and difficulties are experienced in obtaining ducklings of the right quality when required. During discussions on the subject the need for a field manual on combined farming of fish and ducks or pigs was emphasized.

Combination of aquaculture with agriculture

The most common form of aqua-cum-agriculture is combined cultivation of fish and rice. Basically there are many advantages in combining these forms of food production. However, since rice cultivation is the main concern, fish culture has to be adapted to the requirements of rice production such as water level, draining, harvesting, etc. Ricefield fish culture, and to a lesser extent some form of shrimp and prawn production in ricefields, has existed in some Asian countries for many years. It has been tried in a number of countries in Africa and is practised widely in Madagascar. At least four countries in Europe, two in Latin America and some of the southern states of the U.S.A. have adopted this type of culture on a limited scale. Depending on the nature and level of operations, fish production ranges between 100 and 2 250 kg/ha. In none of these countries has there been any expansion of ricefield fish culture in recent years; on the contrary there have been definite signs of decline in many. Some of the main reasons for this are the use of high doses of fertilizers, persistant pesticides and herbicides; increasing use of high-yielding short varieties of rice in fields maintaining low water levels; and fragmentation of ricefields in some countries due to land settlement and inheritance laws. However, the possible benefits from the use of ricefields for fish culture in developing countries that are in dire need of increasing the production of animal proteins are so great that the temptation to conclude that modern rice cultivation practices are incompatible with fish culture has to be resisted. Even if only a small percentage of the existing irrigated ricefields were to be used for this purpose, the resulting increased production of fish would be appreciable. Possible means of reconciling the conflicting requirements have therefore to be investigated with a view to developing an appropriate technology for combined culture. As was pointed out in Session I of the Conference some progress has already been reported on the development of insect-resistant strains of rice which may lead to the reduction or elimination of the use of insecticides. The root application of insecticides and the use of pre-fermented fertilizers also appear promising.

Combination of aquaculture with agriculture and animal husbandry

While in most cases attempts are made to combine aquaculture with either agriculture or animal husbandry, there are a few cases where integrated systems combining all three are practised. Such a system offers many possibilities for the profitable use of ponds and adjacent land areas for production of fish, vegetables, cereals, poultry, pigs and even cattle. In some areas even silviculture can be practised in conjunction with pond farming. Such integrated systems are of special significance in rural development programmes and deserve support of national governments and international funding agencies. Appropriate planning of the various activities will be essential if the system has to be integrated and harmoniously implemented to achieve maximum production and optimum use of resources. The necessary infrastructure and support services have to be made available besides adequate financing and managerial skills. Benefits from integrating various forms of animal, plant and fish culture should be demonstrated and potential protein yields established.

(Section 5)
Aquaculture in Raceways, Cages and Enclosures

V.R. Pantulu
A.G. Coche

Panel Members

J. Kato:Design of aquaculture installations
D. Møller:Cage and enclosure culture
M. Delmendo:Comparative economics of cage, raceway and enclosure culture
V.R. Pantulu:Potentials for the expansion of cage and enclosure culture in developing countries
Relevant Documents:FIR:AQ/Conf/76/R.15, R.20, R.26, R.37,
/E.5, E.10, E.19, E.30, E.32, E.35, E.43, E.51, E.53, E.54, E.72, E.73

The culture of fish in cages, enclosures, raceways or other types of running-water aquaculture systems is relatively old in some parts of Asia. Its significance and application have, however, become specially relevant under present-day conditions. Much of current aquaculture is land-based and availability of land near sources of adequate and suitable water supply is fast becoming a limiting factor in industrially advanced, as well as some of the developing countries, of the world. Other countries are also likely to be faced with such a situation in the not too distant future and this has led to what may be termed a rediscovery of such systems. Through experimentation and innovations they have been very considerably improved and adopted on a commercial scale in many developed countries.

Sites for cage and enclosure culture

Cage or enclosure culture is generally carried out in protected bays, lakes, reservoirs, small rivers or irrigation canals. While in most countries there are still enough sites available for such types of development, in those areas where culture operations have expanded, crowding of cages or construction of too many enclosures have tended to affect water circulation and increase silting. There are also cases where serious water pollution problems have arisen due to crowding of cages in enclosed areas. Consequently there is now a tendency to move them off-shore and this calls for considerable engineering inputs. Studies are underway in Japan to develop suitable off-shore floating breakwaters of the rigid and flexible types. An experimental “sea ranch” enclosed by netting has been in operation in Japan for some time and it produces about 500 tons of yellowtail (Seriola) annually. It is submerged off-shore for protection from typhoons. Legal and environmental considerations are of particular importance in the siting of such installations.

Cage and enclosure culture

Cages and enclosures of different designs have been developed in recent years and successfully used. Salmons (Oncorhynchus, Salmo), trout (Salmo spp.), channel catfish (Ictalurus) and yellowtail are the most commonly used species for modern cage culture. In traditional practices local species of catfish and common carp are used in some Asian countries. The culture of milkfish in pens has developed on a large scale in the Philippines in recent years. Cage culture of tilapia has also been undertaken on a small scale in a number of places. The floating net-cage culture method adopted in Japan, which accounts for a production of about 100 000 tons annually from some 7 000 cages, was considered capable of being utilized in developing countries. The problems of fouling and erosion of nets are now receiving special attention. In the Federal Republic of Germany this problem has been overcome by the use of rotating globular cages. In the majority of cases, particularly in cage culture, production is to a very large extent dependent on feeding efficiency. The nature of the site and environmental factors, especially dissolved oxygen, velocity and circulation of water, are also important factors. Modern developments in these types of culture are largely restricted to developed countries. The exception is the pen culture of milkfish in the Philippines, which has expanded very considerably in a short period of time. The main constraints to the wider application of these systems in other developing countries appear to be the lack of adequate financing, availability of suitable feeds and technical support. There is also the need to demonstrate modern methods of cage, enclosure/pen and raceway culture for which pilot projects have to be established in key localities. During discussions on the subject, it was suggested that a manual on cage culture should be prepared, incorporating details of different cage designs, culture techniques and economics of operations. The representative of “The Commercial Fish Farmer and Aquaculture News” reported that the journal will be publishing a series of articles on cage culture later this year and will be glad to include a catalogue of cage designs.

Comparative economics of cage, enclosure and raceway culture

Although cage, enclosure/pen and raceway cultures all have their application in fish and shellfish production, the economics of operations will be an important factor in their adoption on a wider scale. Of the three methods, raceways require the highest initial capital costs and cages the least. However, when the capital costs are amortized, enclosures/pens used for extensive culture involve the highest annual costs. This points to the need for research directed toward reducing initial capital costs without losing efficiency or increasing maintenance and annual operating costs. Feed cost is the single highest annual production cost in all three methods and averages over 55 percent. The use of herbivorous or plankton-feeding species in enclosure culture may serve to reduce feed costs, but this is possible only in waters of high primary production as in Laguna-de-Bay in the Philippines. Labour constitutes a relatively high cost in enclosure culture because of harvesting costs. The protection of the stock from poaching or theft is a widespread problem and the cost of this can be significant.

There appears to be no significant difference between the three types of culture in the biological aspects, such as feed conversion, growth rate and survival, if the water quality is favourable and the culture techniques are followed properly.

In discussing the potential for expansion of these forms of high density culture worldwide, the session considered sub-tropical and tropical lagoons as of special importance. In order to meet the growing demand for fish in urban areas, it will be advantageous to establish such intensive culture systems in the neighbourhood of towns and cities. It was suggested that planners of future cities should be encouraged to incorporate facilities for intensive fish culture in their plans. In developing countries where these practices are currently used, steps should be taken to provide necessary technical and monetary support to fish farmers who operate these installations. Technical support should be provided for establishing feed mills to prepare feeds using indigenous ingredients, establishing fish nurseries to produce reliable supplies of stocking material and inducing banks to advance loans. In other countries, where these culture systems have not yet been adopted, pilot projects should be implemented.

(Section 6)
Aquaculture in Recirculating Water and Recycling of Wastes in Aquaculture

G.H. Allen
J.E. Stewart

Panel Members

G.H. Allen:Recycling of wastes through aquaculture
J. Tanaka:Use of waste heat in aquaculture
R. Mayo:The use of recirculating water
Relevant Documents:FIR:AQ/Conf/76/R.19, R.30,
/E.3, E.9, E.18, E.19, E.21, E.22, E.23, E.27, E.29, E.37, E.41, E.51, E.59, E.62

Recycling of wastes through aquaculture

The use of certain types of domestic and animal wastes in fish farming is an ancient practice in Asia and continues in at least some of the countries of the region. This can be termed planned use of wastes. Unplanned use of waste water has also been in existence and has been increasing steadily in the last decade. Waste water in drinking water supplies throughout the world, especially in the industrialized world, has reached such a level that there is now serious concern about its possible deleterious effects. Attitudes and approaches to the problem have undergone considerable change and it has become acceptable to discuss the negative as well as positive aspects of it. The many successful programmes of reclaiming waste waters for drinking water accepted by the public health authorities and the general public have now made it possible to discuss objectively the use of waste water as a medium for rearing fish and as a source of nutrients for growing fish or shellfish food. The planned use of waste waters, especially those of domestic origin, is certainly growing in some parts of the world. Many factors have contributed to increased interest in the use of waste waters in aquaculture, the more important of which are:

  1. scarcity of fertilizers and low-cost protein sources for fish feeds,
  2. successful demonstration of polyculture as an efficient waste treatment system,
  3. growing evidence that a well-managed waste water aquaculture system can provide suitable environmental conditions for fish, and
  4. the finding that effluents from waste water treatment lagoon systems containing fish are of higher quality.

Despite all this, the aquaculturists face problems, especially in the utilization of domestic wastes. Concern over the possible accumulation of human pathogens, especially viruses, and their transmission to consumers has to be considered. Depuration techniques have been developed, at least for molluscs. No evidence has been found so far to show that fish cultured in such waters have been harmful when consumed in cooked form, but the fear continues. There is therefore a distinct need for research with the active cooperation of public health personnel to establish the safety of the products. In many areas of the world non-biological problems may seriously limit the acceptance of products reared in waste waters of domestic origin due to social, aesthetic or cultural reasons; efforts have to be made to develop programmes that can overcome these constraints to their planned, controlled and safe use. As a part of a strategy to expand the use of waste waters in aquaculture, it was suggested that when effective depuration cannot be ensured efforts should be concentrated on raising products not meant for direct human consumption, for example bait fish, forage species, juveniles for further culture in other environments and food for larval stages of cultivated species. The active assistance of social scientists may be needed to assess public attitudes and develop scientifically-sound and sociologically-acceptable procedures to promote public approval of such uses, particularly in areas where there are over-riding needs for water, fertilizers and food. As public health hazards generally arise from eating raw or improperly prepared products, waste water aquaculture projects should include an effective programme of consumer education on methods of handling and cooking wastewater-grown aquatic products to break the cycle of human pathogens or parasites.

In a working group session on the subject the recommendations made by the International Conference on the Renovation and Recycling of Waste Water through Aquatic and Terrestrial Systems in Bellagio, Italy (16–21 July 1975) were discussed and endorsed. They were considered to provide the basis for ensured safety and enhanced opportunities for waste-water utilization in aquaculture.

Use of waste heat in aquaculture

The use of waste heat in aquaculture is a relatively new development and has been motivated by the need for:

  1. cheap sources of heat to enhance the growth and survival of cultivated organisms in temperate and boreal climates, and
  2. controlling thermal pollution.

With increasing industrial development and the establishment of thermal and nuclear power stations, the availability of heated water effluents is steadily increasing. During the last 10–15 years much progress has been made in a number of countries in the beneficial uses of the effluents. In Japan cooling water from electric power generating plants averaging about 7°C above ambient water temperature is used in the culture of kuruma shrimp (Penaeus japonicus) and yellowtail (Seriola quinqueradiata) and the seed production of species such as the abalone (Haliotis discus hannai) and the red seabream (Pagrus major). In Hungary the age at first maturity of Chinese carps has been considerably reduced by culture in heated water effluents. In such environments food consumption is increased and higher growth rates achieved, showing improved food conversion efficiency.

All thermal effluents may not necessarily be clean or safe for cultured species. Suitable sites for aquaculture may be difficult to find in the vicinity of power plants. Shut-downs or anti-fouling measures adopted by power plants may render aquaculture in association with them risky. There is often the fear that aquaculture products raised in effluents from nuclear power plants would have accumulated harmful levels of radionuclides. These are some of the constraints, but they can generally be overcome by appropriate joint planning to make full use of opportunities and to reduce risks and costs.

Early in the design phase of any electric power plant, provision should be made for the probable engineering requirements of a thermal effluent aquaculture installation, so that such an installation would not be precluded in advance of the completion of the plant by the prohibitive cost of retro-fitting or other costly modification of plant design. Such provision could include, for example, use of ozone instead of chlorine or other biocides to prevent fouling of intake screens, or the use of titanium instead of brass or other alloys as lining material for condenser tubes.

Detailed comparative studies should be carried out on the ecological, social, economic and engineering implications of various thermal effluent aquaculture installations to provide practical information for appropriate government agencies to aid their future planning.

Studies have also to be carried out on the potential risk and physiological mechanisms of accumulation of radionuclides, heavy metals or other substances in the fish or shellfish cultured in thermal effluents of power plants, including consideration of public health implications and possible remedial methods such as depuration.

The most appropriate way to attain the objectives listed above is through pilot projects in order that design criteria and economic feasibility data necessary for management decisions will become available.

Use of recirculating water

The need for recycling and reconditioning water in aquaculture had also received some attention in previous sessions. The main uses of recycled or reconditioned water are:

  1. to grow more fish with the same amount of water,
  2. to control more economically the environmental conditions in which fish and shellfish are grown, such as temperature, and
  3. to reduce the quantity of effluents so as to minimize post-treatment costs.

Citing the Columbia River hatchery as an example, the development of reconditioning systems in the United States was traced. At present there are some 13 major reconditioning systems in operation in North America. The annual production from these is about 576 tons of salmonids with a total flow through the combined rearing units of 9.3 m3/sec. Despite initial and continuing problems they serve to suggest that reconditioning has a place in aquaculture. This is a clear case where scientific understanding of practices and processes is steadily being enhanced through research contributing to the improvement of the technology. For example, in one study by the Corps of Engineers, a better understanding of the nitrification process was developed. The process involves the conversion of ammonia to nitrate with an intermediate state of nitrite. As nitrification takes place in a heavily loaded system it was found that there was a brief period at startup when nitrite is high, relative to the steady state condition. If the nitrite concentrations were allowed to exceed 0.2 ppm high salmonid mortalities would occur. When this research by the Corps of Engineers provided a basis for understanding the mechanism (and the resulting mortalities), earlier designs and operating instructions were rationally modified and a new level of confidence in reconditioning systems was achieved. Thus understanding followed application.

The aggregate cost of the 13 operative reconditioning systems in North America is in the order of U.S.$ 10 million and the unit capital cost is U.S.$ 40–80/gal (U.S.$ 10.6–21.1/litre) per minute for the more complex systems. Though considered highly economical for hatcheries used for “sea-ranching” programmes, such systems are still too expensive and uneconomical for normal commercial fish farming operations. Future work should therefore be aimed at reducing the cost of the process to enable its wider application. In this connexion the collection and publication of specific data on the effects of metabolites on the growth, survival and health of cultivated species was recommended. Guidelines should be developed, using existing data on salmonids, catfishes, penaeid shrimps or other species on which there is sufficient information, and on the application of bio-engineering criteria to successful recirculating systems. It was also suggested that construction of case histories would illustrate how preliminary modelling analysis for the application of bio-engineering principles has prevented infructuous expenditure of money and effort.

Pollutants from aquaculture installations

During discussions in the working group session on recirculating water and recycling of wastes, the problem of pollution due to aquaculture was raised. It was pointed out that converting ammonia into nitrate may not solve this problem as, if water from the installations were discharged into natural water bodies, serious problems of eutrophication may arise. In cases where closed recirculating systems cannot be adopted it will be necessary to introduce a suitable waste-water treatment system. The denitrification process already used in some places for the treatment of industrial waste water may offer a solution to this. Based on the work carried out in the Battelle Institute in the Federal Republic of Germany, it was reported that denitrification does not pose serious problems when only small stocks of fish are involved. In higher stock densities, of about 10 kg fish/m3 of water, it will be necessary to remove the solid waste from the water and treat only the dissolved substances in the waste water. For large-scale production this is not a satisfactory solution and a closed circulating system which includes an additional denitrification stage was adopted. In the first stage the treatment is based on an activated sludge process. It is followed by an efficient denitrification stage which operates without aeration. Denitrifying bacteria convert the nitrate and nitrite to gaseous nitrogen that escapes into the atmosphere. In this system all the organic waste materials and nitrogen compounds, both solid and dissolved, are converted into carbon dioxide, water and gaseous nitrogen. It was reported that in a small laboratory-scale system it has been possible to maintain 25 kg fish/m3 of water with a growth rate of 1 percent/day.

Nutritional Requirements of Cultivated Organisms and Feed Technology

J.R. Brett
J.E. Stewart

Panel Members

J.R. Brett:Efficiency of protein production through aquaculture
J.E. Halver:Nutritional requirements of cultivated species
B. Hepher:Formulation of feeds and economics of feeding
H. Koops:New sources of proteins for feeds
Relevant Documents:FIR:AQ/Conf/76/R.17, R.23, R.31,
 /E.5, E.6, E.11, E.12, E.23, E.24, E.25, E.30, E.32, E.33, E.36, E.40, E.42, E.43, E.47, E.53, E.66, E.70, E.72, E.79

Efficiency of protein production through aquaculture

The term “efficiency of production” is expressed in two forms:

  1. that most frequently used in the feed industry, in fish farming and in many diet studies, viz. “feed efficiency” or “feed conversion ratio or factor”, expressed as a ratio of weight of “dry” feed (usually 10–30 percent moisture content) to wet weight gain of fish (usually 72–80 percent moisture); and

  2. that used in many scientific reports, viz. “gross food conversion efficiency” or simply “conversion efficiency” which is the percentage of the absolute dry weight gain over the dry weight fed.

Alternatively this may be expressed in terms of nitrogen content or energy content. The first form is the reciprocal of the second when adjusted for relative water content. The highest natural efficiencies recorded occur in the conversion of yolk by the embryonic fish, which can reach 73 percent in herrings. This conversion value ranges right down to 5 percent and less for brood stock of mature fish.

The concept in aquaculture production, for example protein production in ponds, is somewhat different. Here the nitrogen input from fertilizer and other natural processes can be assessed in relation to the nitrogen content of the harvested fish. Observations on herbivores like the milkfish show that a good proportion of the intake is lost in faeces. But the biological productivity of a system which is recycling nitrogen through faeces and bacterial action can greatly upgrade its protein conversion efficiency. The reported feed efficiency of 2.7 of cow manure can be cited as an example.

Most of the contributions to the Conference dealt with the feed efficiency of carnivorous fish. Taking into account the nutritional and environmental principles, it was suggested that a 20 percent efficiency is quite attainable. The basic reasons for low efficiencies were pointed out to be: poor food availability and physiological, environmental and management stress. Under optimal conditions up to 40 percent conversion efficiency has been obtained for young salmon. Recent multifactorial experiments involving combinations of ration level in relation to temperature, salinity and photoperiod in well-oxygenated medium were reported to have yielded subtle optimum combinations that greatly accelerate growth, with improved efficiency of 35 percent and in one case close to 50 percent. Because the first call on food intake is for energy, caution against factors inducing high metabolic rates such as excessive activity, forced swimming, aggression and nervous excitability must be avoided if high efficiency of stored energy is to be achieved. Achievement of target efficiency may similarly be limited by low dissolved oxygen content or accumulation of nitrogenous excretory products, particularly ammonia and nitrite.

An important area of consideration in respect of conversion efficiency is the energy content of the food, the so-called “energy density”. Since fish may expend well over half their food intake in energy and they readily deaminate protein as an energy source, proper balance of digestible carbohydrate and fat is of paramount importance if efficient protein utilization is to be achieved. High conversion efficiencies are achieved by using proteins of high biological value. Further advances in improved efficiency can be expected to couple effective diets with a combination of growth-promoting hormones, environmental manipulation and feeding strategy, based on physiological insight on rate of digestion. If these can be combined with the promise of selective breeding for disease-resistant, docile, domesticated strains of aquatic organisms, the proposed minimum target of 20 percent efficiency can be substantially stepped up.

Nutritional requirements of cultivated species

All finfish so far studied have been found to require the same ten indispensable amino acids in balanced amounts for growth. The remainder of the protein component may be made up of dispensable amino acids but the total has to reflect the amino-acid pattern of tissues being formed for most efficient growth. It should, however, be noted that the specific quantitative amino-acid requirements are known for only a couple of species and mathematical projections based on these for other species have been shown to be erroneous. The need for research to establish the specific values for all culturable species is obvious.

The gross digestible protein requirements have been estimated to be 45–50 percent of the diet for young salmonids, 40–45 percent for ictalurids, 35–40 percent for cyprinids, 35–45 percent for Anguilla and 50 percent for crustaceans. These requirements increase with size and decrease with salinity. It should be repeated that only few species and protein sources have been studied. The preparation of a catalogue of protein sources and the nutritional value of each for cultivated species should receive high priority.

Fats are a ready source of energy for fish and most studies show that fish can use 20–30 percent of the diet as fat and can almost completely digest it. They can thus spare protein which might otherwise be used for the energy cost of living. Many fish appear to need the polyunsaturated C22 or C24 Omega-3 type for good growth and health.

Water-soluble and fat-soluble vitamins are required for metabolism of other nutrients into tissue components. Specific requirements differ between species and new clinical techniques have to be developed to assess the state of health of the species reared. Adequate vitamin intake is often assumed when the diet is supplemented with vitamins, but can only be guaranteed by proper clinical monitoring.

Although not clearly known, minerals are required for the maintenance of salt and water tissue balance, for the metabolism of other nutrients and for major structural elements in the tissues. New tracer techniques and new instruments to measure micro-quantities of elements have been developed and can be used to elucidate the roles of micro-nutrients in normal growth and life processes.

Fish can use fat, protein or carbohydrate to meet energy demands, but the most economical source is carbohydrates. Even if most carnivores are poorly equipped to metabolize sugars and starches, the specific and careful balance of the carbohydrate sources will spare costly protein and in addition furnish optimum amounts of fibre to move other nutrients down the gastrointestinal tract for proper digestion and obsorption.

The session recognized that very little is known of the needs and utilization of these various food components of most of the animals cultured and emphasized the need for research to accumulate the basic knowledge.

Formulation and economics of feeds

In many forms of aquaculture, feeding constitutes a major cost of production, often 40–70 percent of the operating costs. The more intensified aquaculture becomes, the higher the costs for feed also become relative to other operational costs. However, distinction has to be made between systems such as stagnant-water pond culture and flowing-water culture systems and cage culture. In the pond culture system cost reduction can be achieved by increasing the natural productivity of the pond by fertilizing, as natural food forms a major food resource. In the others the fish get very little, if any, natural food and are almost entirely dependent on added feed. The main factors affecting the cost of feeding are composition of the diet and the feed conversion rate. Some studies have already been conducted to determine whether the protein content of feeds could be reduced without loss of food conversion efficiency. The results are not yet conclusive and further work is warranted. But the search for new and less expensive sources of protein has begun. In all the commercially-produced fish feeds, fish meal forms a major source of proteins and accounts for a good proportion of feed costs. Though it is reasonable to upgrade low quality fish in this manner into fish of high market value, it does not receive general acceptance in a strategy for food production to feed the hungry people of the world. Also it has become necessary to reduce feed costs to make certain aquaculture systems economically viable. It was reported to the Session that in experiments conducted in the Federal Republic of Germany, fish meal in trout feeds could be successfully replaced entirely by a mixture of poultry by-product meal and hydrolyzed feather meal, when lysine, tryptophane and methionine were supplemented in small quantities. This is at variance with experience with pig and poultry feeds in which substitution of even 5–10 percent feather meal gave significant growth depression. Partial replacements could also be made with corn gluten meal, a mixture of meat and bone meal, blood meal, alkane yeast or soybean concentrate.

There is need for more concentrated studies on new sources of proteins for fish and crustacean feeds. Possible sources of animal proteins to be investigated were suggested as different types of krill meal and cultured aquatic animals. Single cell proteins, like yeasts, bacteria and algae may be other suitable sources if supplemental amino acids are added. Grasses, leaves and aquatic weeds are other possible sources, but the problems of aromatic fractions or phenol content in grasses have to be solved. In many areas it should be possible to find unutilized agricultural wastes which may be very suitable ingredients for feeds.

In discussing future work relating to the assessment of nutritional requirements of cultivated species and the formulation of feeds, the scarcity of experienced nutritionists and feed technologists was emphasized. It is necessary to develop suitable integrated research and training centres on a high priority basis to fill this need. A comprehensive picture of the nutritional requirements of each priority species at different stages of its life history has to be obtained. In this connexion the usefulness of establishing a centralized data bank with facilities for information retrieval, and also the formation of an international panel of experts, was underlined.

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