Preliminary study of a new virus pathogen that caused the white-gill disease in cultured Larimichthys crocea

By using histopathology and polymerase chain reaction (PCR) methods, studies were carried out to find the cause of the white-gill disease in Larimichthys crocea cultured in cage in Zhejiang Province. White-gill diseased fish had the typical symptom of pale gills and there is no ulcer in the body surface of infected fish. However, the blood and blood cell counts in the white-gill disease fish were significantly decreased. Pathological observation showed serious pathological changes in internal organs. In white-gill diseased fish, haemocytes, in particular, erythrocytes reduced sharply in the blood vessels of liver, spleen and other organs and degenerative changes occurred in red blood cells, too. Under electron microscope, a large number of viral particles were observed in the cytoplasm of spleen, with an average diameter of 40 to 45 nm. With the primers derived from RSIV, no fragments of the RSIV DNA could be amplified from the white-gill diseased fish. The results indicated that although white-gill disease and RSIVD both can lead to the symptom of pale gills, but the pathogen that caused each disease was completely different, and the white-gill disease that broke out in Zhejiang may be associated with another virus.