In situ hybridization of a marine fish virus, Singapore grouper iridovirus with a nucleic acid probe of major capsid protein.

A DNA probe of 531 base pairs for Singapore grouper iridovirus (SGIV) was generated by polymerase chain reaction and labeled with nonradioactive digoxigenin. An in situ hybridization based method was developed to detect SGIV in formalin-fixed tissues from maricultured Malabar grouper, Epinephelus malabaricus Bloch and Schneider. The in situ hybridization detected SGIV in the kidney, spleen, liver, intestine, stomach and gills from naturally infected fish. Strong hybridization signals were obtained from the kidney and spleen tissues, while intermediate intensity signals were observed in the intestine and liver tissues. The weakest signals were obtained from the stomach and gills. The signals were located specifically within epithelial, endothelial and sub-endothelial hypertrophic cells in all tested tissues. The in situ hybridization procedure will provide an important diagnostic tool to complement histopathological methods, and contribute to epidemiological studies on the origin and distribution of iridovirus in mariculture.