HISTOPATHOLOGICAL STUDY OF BLACK BODY DISEASE ON GROUPER REARED IN HATCHERIES

Abstract

Mass mortality of hatchery-reared juvenile cantang-hybrid grouper have occurred in North Bali. The juveniles exhibited mainly black body color with abnormal swimming and slept on the bottom of the tank. Light microscope observation revealed that vacuolation was found in the brain tissue of the fish which showed erratic swimming and rested on the bottom. Moreover, the results of singe step RT-PCR diagnosis using primers specific to the T4 target segments of striped jack nervous necrosis virus (SJNNV) RNA2 genes suggest that this virus is a fish nodavirus. On the other hand, fish with normal swimming were not contained vacuolation in the brain and eyes, and also negative to VNN using single step PCR, which indicated that the fish were likely to be early infected or just recovered from infections. These results also assumed that the virulence of the VNN virus at North Bali waters was increased with the frequent occurrences of mass mortality due to VNN infections. The increase in the virulence was indicated by fast clinical symptoms leads to the black coloration of the body, and the fish were rested and slept on the bottom of the tank. Mass mortality of juvenile cantang grouper had occurred in North Bali. The juveniles exhibited mainly black body colour with erratic swimming (abnormal swimming) and lies on the bottom of the tanks. Histopathology observation showed vacuolation which was found in the brain and eye tissues of the abnormal fish. Moreover, results of single-step RT-PCR diagnosis using primers specific to the T4 target segments of striped jack nervous necrosis virus (SJNNV) RNA2 genes indicated that the fish were infected with a fish nodavirus (NNV). On the other hand, the brain and eye tissues of the normal swimming fish were not contained vacuoles, and also negative to VNN infections.