Molecular detection of betanodavirus in orange-spotted grouper (Epinephelus coioides) broodstock maintained in recirculating aquaculture systems and sea cages

Abstract

Wild collected orange-spotted grouper were domesticated in Recirculating Aquaculture Systems (RAS) and sea cages for fish breeding. While breeding, viral nervous necrosis (VNN) infection was observed in both the systems after 18\xa0months of domestication. Out of 50 domesticated broodfish used in the study, 11 (22%) fishes were found positive for VNN examined by reverse transcriptase polymerase chain reaction (RT-PCR) method. Quantitative real-time PCR (qPCR) study also confirmed the presence of VNN in the suspected fish, and detectable amount of virus copy number was observed in the brain, optic nerve, caudal fin, muscle, and gills. Analysis of the isolated viral gene sequence from the fish was closely related to the red-spotted grouper nervous necrosis virus (RGNNV) genotype and suggests that the isolates are probably endemic to Indian coast. The study also indicated that the sub-adults of orange-spotted grouper infected in the wild and remained as carrier during domestication and subsequently disease outbreak has occurred when water temperature was increased in culture environment. This is the first report on VNN in orange-spotted grouper broodstock from India. The results of the study illustrated that large population of the wild marine fishes are sub-clinically infected with betanodavirus and therefore, early detection of the disease should be adopted as best management practices in breeding for sustainable aquaculture development of the species.