CONSTRAINTS AND PROBLEMS 



Although fish farming is in progress in Japan, 

 some problems and constraints remain. 



Technical constraints include problems concern- 

 ing 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 tech- 

 niques for nutrition of larvae and control of disease 

 and parasites are the most important. Aquatic or- 

 ganisms go through several larval stages with selec- 

 tive 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 fre- 

 quently becomes the limiting factor for seedling pro- 

 duction. Thus, the development of a stable supply of 

 foods for larval stages is necessary for the advance- 

 ment of seedling production. The development of 

 artificial foods is especially needed. 



As the history of aquaculture has shown us, dis- 

 ease and parasite control is also significant. In fish 

 farming, disease control for larva! 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 offish diseases. These kinds of ad- 

 vanced techniques should be applicable to fish farm- 

 ing, but some fundamental problems such as resis- 

 tant 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 artifi- 

 cially reared seedlings are equal to those from 

 natural reproduction. As mentioned before, the re- 

 lease of seedlings is based on the results of prelimi- 

 nary investigations on the environmental conditions 

 of planting area and the behavior of natural or- 

 ganisms. In most cases, the suitability is estimated 

 from the presence of natural larvae indicating a fun- 



damental hypothesis that artificially produced seed- 

 lings 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 in- 

 vestigations, that these places were suitable for 

 farming. These circumstances raise doubts concern- 

 ing the validity of this hypothesis. 



The larvae reared under the ailificial conditions 

 are pampered. They are kept in optimal environmen- 

 tal conditions as far as possible, with adequate food 

 supply, and protected from competitors and pred- 

 ators. 



On the other hand, larvae in natural vsaters must 

 survive the fluctuation of environmental conditions, 

 effects of competitors and predators, and. in addi- 

 tion, they must find food for themselves. Thus, they 

 are hardened in nature. Therefore, it is likely that 

 there are some differences in the biological charac- 

 teristics of natural larvae and artificially produced 

 seedlings as diagrammed in Figure 4. 



In order to obtain more successful results of farm- 

 ing, evaluation of suitability of the receiving waters 

 should include consideration of biological charac- 

 teristics of seedlings. 



There have been suggestions that comparative re- 

 search should be carried out to define the difference 

 in biological characteristics between natural and ar- 

 tificially produced larvae. However, this is some- 

 times impractical because of the difficulty in collect- 

 ing 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 environmen- 

 tal conditions and to observe the effect of these 

 conditions on biological characteristics, such as, re- 

 sistance 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 objec- 

 tives. 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. Al- 

 though this procedure is helpful for adaptation to 

 natural water conditions, it does not train the seed- 



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