Septic conditions account for the majority of bacterial diseases of fishes. For this reason, in fishes, the period from infection with pathogens to their death is short and, therefore, it is very difficult to treat fish diseases excepting the case in which it is possible to diagnose a fish disease early and treat it at its early stage. Pathogens of fish diseases usually live in the water at a fish farm but their pathogenicity is not potent, therefore, they do not cause infection in healthy fish. But when fish become unhealthy and more susceptible to pathogens, they are infected and great damage is caused. As mentioned above, the majority of pathogenic bacteria in fish diseases are facultative pathogens.
To protect fish from various bacterial diseases, it is first necessary to improve the technology for fish culture and to culture healthy fish, which are highly resistant to diseases. Secondly, early treatment methods for fish diseases, as well as diagnostic procedures for early detection of fish diseases, should be established. Thirdly, it is necessary to carry out studies on artificial immunization with vaccine and prevent diseases of cultured fishes. Then it becomes necessary to direct the studies made at the FCRI for the facilitation of the studies in the three above mentioned fields. For this purpose, it is recommended that qualified research workers be trained and facilities, equipment and supplies be provided to fully support these studies.
The most important objectives of the studies should be as follows:
To make studies on optimum nutrition contained in feed for cultured fishes and on the optimum amount of feed to be given to cultured fishes.
To make studies on environmental conditions suitable for cultured fishes and establish a feeding procedure which does cause any trauma in cultured fishes.
To treat cultured fishes in a manner which does not cause any trauma in fishes, since indigenous pathogens invade the body of fish via such trauma.
To make studies on a method to culture fishes which are healthy and highly resistant to pathogenic bacteria so as to inhibit development of diseases.
In order to achieve these objectives, it is recommended that young research workers of the FCRI be sent to Kochi University in Japan for training.
Studies are needed to speed up isolation and identification of pathogenic bacteria. For this purpose, facilities where various pathogenic bacteria are preserved and diagnostic anti-sera are produced should be reinforced. The rapid identification procedure for various pathogenic bacteria, which is used at Kochi University in anticipation of development of new diseases in the future, is shown in Figs. 1 through 11. In addition, a serological diagnostic procedure and a diagnostic procedure using the fluorescent antibody method should be established. For this purpose, it is necessary to provide complete facilities where these studies are made (see Appendix 1 for list of facilities required).
Studies on mass immunization of cultured fishes for the prevention of fish diseases should be facilitated. Mass immunization of fishes may be performed with three types of vaccines, i.e., oral vaccine, immersion vaccine (bath immunization) and spray vaccine. The manufacturing processes and immunization methods for these three types of vaccines, which have proved to be practicable as a result of the studies made at Kochi University, are shown in Figs. 12 through 16. On the basis of these vaccines, studies to develop new immunization vaccines suitable for various fish diseases should be made. Since the effectiveness of immunization vaccines depends on the kinds of fishes and the types of fish diseases, an immunization vaccine should be studied for each kind of fish and for each type of disease.
