Viral and bacterial diseases of marine fish and shellfish in Japanese hatcheries

In Japan, seed production techniques have been exploited 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 marine hatcheries. Among these problems the viral and bacterial diseases with their control measures are reviewed in this paper. Since around the middle of the 1980s, viral diseases such as viral epidermal hyperplasia (herpesvirus infection) in the Japanese flounder, viral ascites (birnavirus infection) in yellowtail, viral nervous necrosis (VNN) (nodavirus infection) in Japanese parrotfish and striped jack, and baculoviral mid-gut gland necrosis (BMN) (baculovirus infection) and penaeid acute viremia (PAV) (unclassified virus infection) in kuruma prawn have been reported. It was demonstrated that the selection of virus-free spawners based on the detection of the pathogen by polymerase chain reaction (PCR) serves as an effective control measure against vertical transmission of the pathogen in VNN and PAV. Vibriosis, pasteurellosis, gliding bacterial infection and other bacterial diseases have occurred in various marine fishes at their juvenile stages. On the other hand, larval fish most frequently develop intestinal infections represented by bacterial enteritis with Vibrio ichthyoenteri in the Japanese flounder. In the last part of the article, control measures for viral and bacterial diseases were discussed in each step of seed production process. (C) 2001 Elsevier Science B.V. All rights reserved.