Study On The Viral Nervous Necrosis In Grouper

In recent years, some cultured groupers in southern Fujian, China have been suffered a fulminant infectious disease causing mass mortalities. The main pathogens and their epidemiological properties were illustrated by using epidemiological investigation. It indicated that the viral nervous necrosis virus has been the most important pathogen infected by the fishes, and heavy mortalities often occur from juvenile to young stages due to this virus. This disease is characterised by a variety of neurological abnormalities such as erratic swimming behaviour and vacuolation of the central nervous tissues and nuclear layers of the retina. The sick or dying fish did not show any pathological signs other than neurological abnormalities, no significant external or internal lesions or parasites were observed. The disease is transmitted both horizontally via the water pathway and vertically via the egg. Vertical transmission from infected spawners is a major route for larvae and juveniles infection. All of the groupers have a high susceptibility to this pathogen, but younger fish have more severe lesions. It outbreaks in special season, generally from March to August every year. More than ten bacteria such as Vibrio alginolyticus, V. parahaemolyticus and V. fluvialis had been identified. Most of them were conditional pathogen that caused secondary infection and made for aggravation of the disease. The Pleistophora and Benedenia were mostly common parasites found in the farmed grouper and made the fish decreased in immunity and resistance to diseases.A regulation of the reverse transcription polymerase chain reaction (RT-PCR) to detect nervous necrosis virus was developed and used in the infection investigation and fish disease quarantine of intro-exit animal in...