As described so far, a considerable amount of studies have been done on various infections in marine hatcheries, and some of the diseases, such as VNN in striped jack and PAV in kuruma prawn, have been well controlled in hatcheries mainly by avoidance of exposure to the pathogens. However, mortality among larvae and juveniles still often occur in marine hatcheries, many of which are due to less virulent viruses like birnaviruses and opportunistic bacterial pathogens like Vibrio species, or due to their combination. These diseases caused by minor pathogens are usually not submitted to detailed investigations owing to a shortage of fish pathologists compared with tremendous number of fish and shellfish species dealt in hatcheries. Therefore, not only major pathogens but also such minor pathogens should be put on the stage for concentrated
investigations.