Status of Fish Culture
In reviewing the present status of fish culture in different parts of the world, the Symposium recognized that the major developments in the field have taken place mainly in areas where there has been a tradition of fish culture or in areas where people with such a tradition have settled. Although it has been demonstrated that fish culture can make very substantial contributions to the food supply and economy of countries and form a valuable and integral part of land and water development projects, there has also been a large number of significant failures of fish culture programs. It was recognized that such failures have resulted mainly from over-selling and the over-ambitious and ill-balanced nature of programs undertaken without appropriate surveys and pilot studies. Although it is true that fish culture requires less investment and skill than many other means of food production, the over-simplified picture of fish culture activities often presented by enthusiasts can do irreparable damage to fish culture development and should be discouraged. Participants from all parts of the world agreed that the training of personnel at all levels should be given high priority for the success of fish culture programs, and in this connection stressed the need for regional manuals of the type that FAO has recently published in cooperation with the United Nations Children's Fund (UNICEF) 1.
Discussing the over-all possibilities of commercial fish culture, the vast areas of coastal and estuarine tidal lands and swamps were identified as offering unique opportunities for reclamation into fish ponds and for production of food fishes, crustaceans and molluscs. Brackish-water fish culture has not yet received the attention it deserves in most countries of the world and it was felt that wherever facilities existed, special efforts should be made to develop this industry.
Fish Culture Statistics
In reviewing the progress of fish culture development and in assessing the results of developmental programs, the lack of adequate statistics came into particular focus. Data required for proper economic evaluation of the effectiveness of different techniques or of the industry itself were conspicuous by their absence in most areas. The Symposium felt that efforts should be made to collect and compile such data and publish these regularly.
Fish Pond Soils and Fertilizers
In spite of their great influence on water quality and on the nutrient cycle in ponds, the characteristics of pond soils have not been studied in any great detail. This was recognized to be due largely to the insufficient number of soil scientists associated with fish culture research and lack of facilities in many of the research centres for soil studies. The Symposium agreed that the study of soils should be fully encouraged. It was felt that the extensive literature that exists on rice field soils could be of great value in the investigations on fish pond soils and should be utilized by fish culture workers.
Use of fertilizers was recognized to be the most economical way of increasing production in ponds, but the fertilizer requirements of ponds vary so widely that there can be no universal pond fertilizer. However, the data presented at the Symposium clearly showed that phosphate was the most important limiting factor in practically all pond waters. With regard to the use of nitrates, there appears to be a clear difference between tropical and temperate zones. Addition of nitrates gives rise to better production in temperate zone ponds, especially during the cold months, whereas in tropical ponds there is very little response to added nitrogen, probably because in the existing higher temperatures nitrogen fixation by bacteria or by blue-green algae is adequate to meet the nitrogen requirements.
Though considerable attention has been paid to the study of fish pond fertilizers in recent years, much more work is required, especially on the exact fate of fertilizers applied to ponds, nitrogen fixation agents, effect of fertilization on the relative abundance of desirable algae, lime requirements and the effect of various levels of hardness upon phosphorus fixation and the composition of the biota.
Feeds and Feeding
Very high production reported from ponds has invariably been obtained by intensive artificial feeding and this has proved to be a very efficient means of converting low quality agricultural products and waste material into high quality protein. Fish can be grown mainly on artificial feeds as in running water ponds, or partially on artificial feeds that supplement the natural foods. The availability and cost of feed are the main limiting factors in their wide-spread use, especially in developing countries where there is a shortage of agricultural products commonly used as fish feeds.
As there is an over-riding need to obtain the maximum production per unit area from ponds, particularly in countries that are backward in agricultural production, it is urgently required to evolve a process to prepare a nutritive fish feed from organic wastes or other easily and cheaply available materials. Microbial digestion and biosynthesis were indicated as processes to be tried. There was general agreement that research on this aspect should receive very high priority. To make feeding operations economical, it was considered essential to develop efficient and cheap formulations of feeds for use even in countries with fish feed resources.
Breeding and Selection
The documents presented at the Symposium and the discussions that ensued clearly showed that most of the research work carried out on this aspect of fish culture and the field experience that has accumulated, relate largely to the breeding of fish in ponds or under controlled conditions. The prevention or control of spawning has received very little attention even though it is of great importance in fish culture operations.
The need for genetic selection to obtain stocks with the required form, growth, food conversion and resistance properties was brought out during the discussions and it was observed that very few countries in the world have at present effective selection programs. This is attributable to a very large extent to the lack of appreciation of its importance and the paucity of specialists in this field among fish culture biologists.
The usefulness and need for hybridization as exemplified by the tilapia (Tilapia spp.) hybrids were fully recognized, but the Symposium cautioned against indiscriminate attempts at hybridization and appealed to workers that hybrids that did not possess the required qualities should be destroyed and not allowed to enter natural bodies of water.
Biological Means of Increasing Productivity
The comparative merits of various biological methods of increasing production in ponds were considered. Species combinations, use of fast growing species, multiple stocking and multiple harvesting which have been in practice in many parts of the world, still remain the proven means of increasing yield from ponds.
Weed Control
The eradication of water weeds is a problem of world-wide importance insofar as fish ponds are concerned, but there are considerable differences between countries and regions in its relative importance. Clearance of weeds from ponds forms a major operation involving a considerable proportion of maintenance expenses of ponds in some areas, whereas it is of low significance in others. There was general agreement that biological methods of weed control are the best to be adopted in fish ponds, but it was also recognized that in many situations a combination of techniques including the use of herbicides may have to be employed. Further research is urgently needed to formulate more efficient, safer and cheaper herbicides.
New Systems and New Fishes for Culture
Of the new systems of fish culture that have developed in recent years, the use of enclosures, made of netting or other materials, in natural bodies of water such as lakes, received particular attention. This system enables rearing very dense populations and can raise production to a very high level, avoiding such attendant dangers as pollution, disease, etc. The high costs of pond construction and maintenance can also be minimized. In colder climates, this system enables the utilization of the warmer waters in the top layers of lakes and similar bodies. In running waters such as irrigation canals the culture of fish in cages and large baskets holds great possibilities of extension.
Culture of common carp (Cyprinus carpio) in tanks with recirculating water system, developed in Japan, though still in an experimental stage may prove of great value in areas with limited water supplies, if the capital and running costs of the installations are not too high.
With respect to the species used for culture, the data assembled at the Symposium showed that even though some new species are now used for culture in certain parts of the world, the main-stays of fish culture continue to be species that have been under cultivation from olden times. Even though these fishes have proved most valuable, it is obviously necessary to find new cultivable species to meet consumer preferences and to build up species associations to fill unoccupied ecological niches. It is highly desirable that fish culturists devote greater attention to this aspect of studies.
Diseases and Parasites
With the adoption of more and more intensive methods of fish culture, the hazards of fish diseases and large-scale mortality are increasing. International exchange of fishes is also increasing rapidly, resulting in greater hazards of new diseases and introduction of parasites in areas where they do not occur. Even though there is a definite need for expanded research to identify causal agents of diseases and develop efficient methods of control, the use of disease-resistant strains for culture should be encouraged as far as practicable and in this connection selective breeding is of special significance.
The Symposium recognized the need for proper controls to prevent the spread of parasites and diseases and in this connection supported the recommendation made by the Fourth Session of the European Inland Fisheries Advisory Commission (EIFAC), Belgrade (1966) to survey the laws and regulations governing imports and exports of live fish and fish eggs and suggested that all countries of the world should be covered in such a survey.
Future Research
The reviews of existing information and the discussions that took place in the Symposium focussed particular attention on the wide gaps in knowledge in many aspects of fish culture and the need for critical researches using comparable, if not standardized, techniques. To improve the quality of research carried out in fish culture and the adoption of standardized techniques in research, it will be extremely useful to have a manual of fish culture research methods.
Considering the fact that there are only a small number of fish culture research institutions in the world with adequate facilities for detailed experimental studies, close cooperation between institutions was considered essential to enable full utilization of resources. FAO could promote such cooperation by the quick dissemination of information on current research programs through a directory to be revised at regular intervals and the results of research and extension through a newsletter.
Investigations of most of the existing fish culture research institutions are tied up with production programs and consequently very little long-term basic research in fish culture has been carried out. The Symposium recognized the need for basic research and felt that every effort should be made to stimulate such work and noted with satisfaction the importance given by the International Biological Programme (IBP) to the study of the productivity of fish ponds.
Special attention was devoted to the alleged public health hazards of fish culture and emphasized that there should be close cooperation between public health and fishery workers in ensuring the prevention of such hazards if they exist and that studies in this field should be coordinated at an international level.
The Symposium was unanimously of the opinion that FAO should assume a leading role in the promotion and international coordination of fish culture research and development policies, for which it should have adequate fish culture staff and the benefit of advice from a panel of experts. If actions as formulated at the Symposium are taken, it was estimated that in about five years' time there would be sufficient advances in knowledge in the field of warm-water pond fish culture to warrant holding another world symposium on the subject.
