Geographically and historically, utilization of marine products, which has been quite significant to the Japanese people and fisheries, is one of the most important industries of the Nation.
Before the World War II, Japan expanded her fishing area and Japanese fishermen worked all over the world to obtain their foods. The catch was mainly consumed as the protein source for nutrition of the people, and the expansion of production was most important. This situation continued until about a decade ago.
During recent years the situation has changed remarkably. The Japanese people have demanded greater variety of fishery products of high quality with improvement of their living standard. However, high-quality species occur along the coast of our homeland, and these stocks had decreased because of overfishing and/or water pollution. Under these circumstances, fish farming has become necessary.
In 1962, the Seto Inland Sea Farming Fisheries Association was established, and by 1966 five operation centers were completed and began operation. At present, the tasks of fish farming are expanding as scheduled, but some problems remain. Through cooperative research, biologists and fish farming specialists are searching for solutions to these problems in order to advance the operations. Fish farming is somewhat different from ordinary aquaculture. The differences are explained briefly and some constraints are discussed in this paper.
When the Seto fish farming operation was started, it was planned to release the larvae following the procedures used with salmon and trout. At that time the Inland Sea was regarded as a fish culture pond, and early stages of larvae were released directly from the operation centers without any care because no effective technique had been developed for rearing marine fish through their larval stages in captivity.
Subsequently, it became apparent that more effective utilization of artificially produced larvae was required, and some new techniques were developed for larval culture and for acclimation to natural waters. Also, procedures were developed for maintaining a brood stock in captivity for earlier production of seedlings and production of more healthy seedlings. As a new idea, some civil engineering techniques were proposed to rehabilitate growing and releasing grounds.
Thus, the present farming fisheries are really equivalent to agriculture in water areas. Artificially produced seedlings are held or planted in shallow coastal regions, and these seedlings utilize natural productivity of these waters for their growth. Recapture or harvest occurs within a certain period (Fig. 1) when the products are ready for market.
In this process, the utilization of natural productivity is an indispensable condition for farming fisheries which is different from ordinary aquaculture in which the growth of species, such as trout and eels, depends almost entirely upon introduced foods.
The following items are considered in selecting suitable organisms for farming:
As a special case, geographical transplantation of organisms is ideal for some species. Rapid growth and greater production can be expected when northern species are transplanted to southern regions. Some places isolated from a source of organisms sometimes have few native species, but have food and space capacity for additional species. So, when the investigation for farming is carried out, the idea of introducing a new species should be considered.
Present and/or proposed farming fisheries could be classified into two types: 1) stock recruitment and 2) artificial control. as shown in Figure 2.
In stock recruitment type of farming. the seedlings are transferred from the operation centers or hatcheries to a temporarily constructed acclimation facility. This procedure allows the seedlings to adapt to the environmental conditions of the receiving waters and to naturalize their behavior while protected from predators. After certain periods, they are released into natural waters forgrowth. In this case, the planting sites are determined from the results of scientific investigation of the environments and distribution and behavior of natural stocks.
For example, when a shrimp release program is planned, investigations are carried out in advance to determine the suitability of various places for shrimp growth and the best place is selected for the planting. Places where natural shrimps thrive are likely to be satisfactory release sites.
When environmental conditions in an area are acceptable for the planned species and when results of scientific investigations show that the adaptation and the naturalization are unnecessary, seedlings are released directly into the waters. Otherwise, acclimation techniques are applied. In the case of shrimp, the seedlings are acclimated in net enclosures for 1-3 wk depending upon the situation.
The stock recruitment type of farming is practiced at present with prawn. blue crab, and several species of fin fish.
The artificial control type of farming is usually smaller in scale than the stock recruitment type, and frequently some facilities or mechanical equipment are involved. The farming of oyster, abalone, clam, algae in Japan, and of ~milkflsh in South Asian countries are of this type.
A new experiment in the culture of red sea ~bream is based on conditioning the fish to respond to sounds. The seedlings, 20-50 mm in total length, are kept in floating cages and trained with sound and feeding of pellets. Within 2-8 wk, they are adapted to sound of certain frequency (100-600 Hz) and develop the habit of gathering around a feeding place every time the sound discharges. After they obtain this habit, the fish are liberated into natural waters, and most of them retain the habit and do not scatter. Although a small amount of pellets is necessary to feed them, they can eat more natural foods for their growth. Therefore, this idea could be categorized as a fish farming.
The first step and one of the key points of fish farming process is the seedling production. At the incipient period, zygotes, larvae, and young fish collected from natural waters are mainly used as seedlings, but artificial seedling production techniques have been developed for important species and these techniques are applied for the actual farming operations. The process is briefly shown in Figure 3.
Matured adults from wild stocks are still used to obtain eggs and sperm in most cases, but research to develop techniques for obtaining eggs from adults reared to maturity in captivity are in progress.
In order to obtain zygotes, stripping and artificial spawning methods arc sometimes used, but most species can be induced to spawn naturally in artificially controlled tanks. Matured adults are put in a tank of water, and the zygotes are collected after spawning and fertilization occur. Then, the eggs are transferred into a rearing facility such as a tank or aquarium. For some species, matured adults are put directly into the larval rearing tank and removed after spawning.
The zygotes are reared in tanks of still water, but slow running water can be used for larvae after they reach certain sizes. With some species, the larvae are transferred to floating cages until they reach seedling size, but with shrimp, the larvae are kept in the same tank till they reach seedling size. In this case, control of population density to achieve the desired numbers of final stage is important. The size of seedlings varies depending on the purpose and environmental conditions of receiving waters.
The planned numbers of seedlings to be produced in five centers in 1971 fiscal year are shown in Table 1. The prefectural centers are also producing some seedlings, but their main purpose is the development of culture methods.
Although fish farming is in progress in Japan, some problems and constraints remain.
Technical constraints include problems concerning seedling production, nutrition of larvae, disease and parasite control, and feeding. Among these, seedling production techniques are being developed rapidly, and experience with the successful culture of several species should be applicable in the future to other species. Among other problems, however, fundamental research for the advancement of techniques for nutrition of larvae and control of disease and parasites are the most important. Aquatic organisms go through several larval stages with selective food habits, and the most suitable food has to be found for each stage. At present, phytoplankton and zooplankton cultured and/or collected from natural waters are fed to the larvae, but the supply frequently becomes the limiting factor for seedling production. Thus, the development of a stable supply of foods for larval stages is necessary for the advancement of seedling production. The development of artificial foods is especially needed.
As the history of aquaculture has shown us, disease and parasite control is also significant. In fish farming, disease control for larval stage will have to be developed. Usually, larvae are weaker than adults, and contagious diseases are most serious. It is not unusual to have several millions of larvae killed during a short-time period in actual farming.
In aquaculture, practical methods for treatment of diseases and parasites have been developed. For instance, chemotherapy has assisted the treatment and prevention of fish diseases. These kinds of advanced techniques should be applicable to fish farming, but some fundamental problems such as resistant strains and human public health considerations remain.
As an effective method for preventing disease mortality, it may be possible to breed resistant strains but little research has been done for this purpose.
The most significant constraint concerning the utilization of seedlings is the hypothesis that artificially reared seedlings are equal to those from natural reproduction. As mentioned before, the release of seedlings is based on the results of preliminary investigations on the environmental conditions of planting area and the behavior of natural organisms. In most cases, the suitability is estimated from the presence of natural larvae indicating a fundamental hypothesis that artificially produced seedlings are equivalent to natural larvae. However, the results of farming trials along the coast of the Inland Sea and surrounding districts have been variable. Successful results have not always been obtained in spite of the determination, based on preliminary investigations, that these places were suitable for fanning. These circumstances raise doubts concerning the validity of this hypothesis.
The larvae reared under the artificial conditions are pampered. They are kept in optimal environmental conditions as far as possible, with adequate food supply, and protected from competitors and predators.
On the other hand, larvae in natural waters must survive the fluctuation of environmental conditions, effects of competitors and predators, and, in addition, they must find food for themselves. Thus, they are hardened in nature. Therefore, it is likely that there are some differences in the biological characteristics of natural larvae and artificially produced seedlings as diagrammed in Figure 4.
In order to obtain more successful results of farming, evaluation of suitability of the receiving waters should include consideration of biological characteristics of seedlings.
There have been suggestions that comparative research should be carried out to define the difference in biological characteristics between natural and artificially produced larvae. However, this is sometimes impractical because of the difficulty in collecting samples of natural larvae. In some species, the natural larvae have not been observed and, with the present state of knowledge, could not be identified even if some larvae could be found. The best method is to experimentally establish expected environmental conditions and to observe the effect of these conditions on biological characteristics, such as, resistance to the fluctuation of environments, physiological activity, avoidance reaction from predators, and ability of shrimp and crab to bury themselves in the bottom sediments.
Techniques for acclimating artificially produced seedlings should be varied with the species and the results desired. At present, almost standardized facilities and methods are used for acclimation of seedlings without adequate consideration of objectives. These include net enclosures and net cages for shrimp and crab and floating cages for fish, in which seedlings are kept with feed for several weeks. Although this procedure is helpful for adaptation to natural water conditions, it does not train the seedlings to find natural foods or to avoid predators. Conditioning and training, based on biological requirements to achieve the intended purpose, should be tried in the acclimation facility; otherwise, successful acclimation cannot be expected.
The greatest problem connected with the future of fish farming is the pollution of natural waters. Although water pollution is a matter of concern among the people and plans for pollution control are being developed, the adverse effect on fish farming is not fully recognized.
Some aspects of this biological problem have been investigated to find ways to reduce the effects of pollutants on-fisheries, and water quality criteria and water quality standards have been described for some aquatic organisms. However, most of the research data are on adult organisms.
In fish farming, the situation is more severe. For example, the period of larval development is the weakest stage of the life history of organisms, and even seedlings have lower resistance to pollution than adults. Brood stocks require a high quality of water to maintain healthy adults which will produce active larvae.
As the mass production of seedlings is possible, a limited number of hatcheries can supply the demand for seedlings. Places chosen for hatching facilities should have the best environmental conditions in unpolluted regions. Farming, especially of the stock recruitment type, requires extensive areas of unpolluted water for the production of large amounts of fish or shellfish. Complete water pollution control will be needed to keep released organisms safe. For this purpose, the cooperative research will have to be carried out by fishery biologists and specialists on pollution control. Without this cooperation the advancement and expansion of fish farming will be hopeless.
The history of aquaculture in Japan is quite long. Mariculture of oysters and algae was started sometime before the beginning of science. Procedures were established by fishermen, and the techniques have been developed and reformed year by year based on their experiences.
Since the beginning of fisheries science about a century ago, the scientists have verified the suitability of techniques developed by fishermen, though some technical contributions have been offered. Therefore, it cannot be said that scientists have developed the fundamental concepts for the advancement of aquaculture.
Considering the period in which it was developed, the idea of fish farming should be esteemed highly as an epochal accomplishment. At the present time, however, ancient and new ideas of aquaculture in Japan are mixed together. These ideas should be reorganized systematically to establish efficient operation plans and research projects.
Among the old aquaculture techniques, there are some helpful ideas and methods for the development of new farming fisheries. For example, an artificial fish shelter of concrete blocks is an effective method to build a new fishing ground. A larger scale shelter would form an "artificial bank." If the technology of artificial shelter or bank and fish farming could be combined, greater fish production may be expected. Therefore, the combination of differently categorized ideas or techniques will accelerate the advancement of practical fish fanning.
Fish farming is becoming of global interest and Japan is considered as the most advanced country in this field. People concerned with fish farming and ~aquaculture expect to obtain the information from Japan, and sometimes they are apt to apply the Japanese methods and techniques directly. Biological techniques are so complicated, however, that direct application in other environments may be unsuccessful and some modifications will be required. Certainly fish farming should be encouraged on a universal basis, but many problems remain to be solved. Greater advancement can be expected with the international cooperation of experts in this specialized field.
1 Nansei Regional Fisheries Research Laboratory, Maruishi, Ohno-cho. Saeki-gun. Horoshima-ken. Japan.