EXPERIMENTAL-INFECTION OF ATLANTIC HALIBUT, HIPPOGLOSSUS-HIPPOGLOSSUSL, YOLK-SAC LARVAE WITH INFECTIOUS PANCREATIC NECROSIS VIRUS - DETECTION OF VIRUS BY IMMUNOHISTOCHEMISTRY AND IN-SITU HYBRIDIZATION

Three different concentrations (10(7), 10(5) and 10(3) TCID50 ml(-1)) of infectious pancreatic necrosis virus (IPNV) serotype Sp isolated fr om Atlantic halibut, Hippoglossus hippoglossus L., were used to bath-c hallenge Atlantic halibut yolk-sac larvae. The larvae challenged with 10(7) TCID50 ml(-1) suffered significantly higher cumulative mortality than the other challenged groups and the control group, and affected individuals displayed necrosis of the intestine, liver and kidney. In larvae from the groups challenged with 10(7) and 10(5) TCID50 ml(-1), IPNV was detected by immunohistochemistry and in situ RNA/DNA hybridiz ation in the intestine, liver and kidney. In addition, some individual s stained IPNV-positive in the heart and eye/brain region. Detection b y in situ hybridization did not appear to be more sensitive than immun ohistochemistry. However, background staining was virtually absent in comparison with immunohistochemistry, and the staining seemed to be mo re distinctly localized to the cytoplasm of infected cells. The result s show that farmed halibut yolk-sac larvae can be infected by IPNV imm ediately after hatching, with resulting high mortality. As the larvae are not immunologically mature at this stage of development, vaccinati on is not recommended.