Abstract

Fish nodavirus was first isolated in moribund grouper larvae at 1994 in southern Taiwan. The outbreak of viral nervous necrosis disease among grouper larvae and juveniles has occurred every year. In this study, we screened many species of hatchery-reared or cage-reared fish in Taiwan for nervous necrosis virus (NNV) infection in order to know the spread and the evolution of fish nodavirus among warm water fish. Twenty species of fish have been examined by RT-PCR and semi-nested PCR using primers specific to T2 and T4 target region of NNV capsid protein gene. Twelve species of fish, belonging to three orders, seven families and eight genuses, were found to be NNV natural hosts with or without outbreak of mass mortality. Nucleic acid extracted from the brain tissue of barramundi (Lates calcarifer), hump-back grouper (Cromileptes altivelis), yellow-wax pompano (Trachinotus falcatus), European eel (Anguilla anguilla L.) and cobia (Rachycetron canadum) were amplified using T2 specific primers, sequenced, and compared with other Taiwan isolates from groupers (Epinephelus sp.) and Japan isolate red-spotted grouper nervous necrosis virus (RGNNV). Nucleic acid alignment and amino acid alignment of T2 region among the above NNV isolates revealed high similarity (>98%), and all belong to RGNNV genotype. The distribution of point mutation of those NNV isolates is random. These results showed that GNNV has low host specificity among warm water fish, and is highly possible to be the cause for the spread of VNN disease among other fish species reared in Taiwan. Moreover, Hump-back grouper, yellow-pompano, European eel and cobia are first reported to be NNV host around the world.