VIRAL AND BACTERIAL DISEASES IN LARVAL AN D JUVENILE MARINE FISH AND SHELLFISH - A REVIEW

In Japan, seed production techniques have been developed for about 80 species of marine fish and shellfish. However, mass mortalities due to infectious and non-infectious diseases have often occurred in larvae and juveniles reared in hatcheries. Among these problems the viral and bacterial diseases are reviewed in this paper. Since around the middl e of 1980's some new viral diseases such as viral epidermal hyperplasi a (herpesvirus infection) in the Japanese flounder, viral ascites (bir navirus) in yellowtail, viral nervous necrosis (VNN) (nodavirus) in st riped jack and some other fishes, and baculoviral mid-gut gland necros is (BMN) in kuruma prawn have been reported. It was demonstrated that the selection of virus-free spawners based on the diagnosis by polymer ase chain reaction (PCR) could serve as a control measure against vert ical transmission of the pathogen in striped jack. Vibriosis, pasteure llosis, gliding bacterial infection and other bacterial diseases have occurred in various marine fishes during their juvenile stages. On the other hand, larval fish most frequently develop intestinal infections represented by bacterial enteritis with Vibrio sp. INFL in the Japane se flounder. Live foods contaminated with pathogenic bacteria have bee n suspected to serve as an important source of these intestinal infect ions.