Marine parasitology with special reference to Japanese fisheries and mariculture

Marine parasites with special relation to Japanese fisheries and mariculture include various types of pathogens: those causing mortality, deformity, weight loss, etc.; those giving unesthetic appearances to the hosts; those which are zoonotic. Japanese mariculture typically utilizes net cage culture systems in coastal areas. Parasite invasion in such systems is more difficult to control practically than in freshwater facilities. The limited use of chemicals and drugs for treatment makes the situation even more difficult to handle. About five species of parasites from marine organisms are known to be zoonotic. This is closely associated with the Japanese tradition of eating raw fishes and invertebrates. Infection of maricultured species with zoonotic trematodes, cestodes and nematodes has not been confirmed. On a more positive side, attempts have been made to utilize parasites as biological tags to obtain information on host biology, ecology, etc. Recent trends in Japanese mariculture include technical improvement in seed production and importation of large quantities of various species of culture seedlings. Drastic increase in the supply of seedlings of selected fish species has resulted in changes in culture methods and created parasite problems on a much larger scale. International trade of live fishes and shellfishes has introduced parasites hitherto unknown to Japan. An efficient quarantine system to prevent and control introduction and spread of marine parasites urgently needs to be established.