HEPATIC MEGALOCYTOSIS IN WILD AND FARMED CHINOOK SALMON ONCORHYNCHUS-TSHAWYTSCHA IN BRITISH-COLUMBIA, CANADA

Hepatic megalocytosis in fish has been used as a bioindicator for expo sure to xenobiotics. However, this lesion is also induced by natural t oxins and has been observed in fish from apparently unpolluted waters. Hepatic megalocytosis was observed in 16.0 % of chinook salmon Oncorh ynchus tshawytscha that had returned to spawn at 3 freshwater hatcheri es on Vancouver Island, British Columbia (B.C.), Canada, and was obser ved in 7.0 % of ocean-caught chinook in this area. The lesion was not detected in 175 wild-caught sockeye salmon O. nerka. A greater proport ion of wild chinook were affected when compared to farmed chinook of a similar age that were reared in seawater netpens (12.3 vs 1.5 %). Thi s survey demonstrates that hepatic megalocytosis is prevalent in wild chinook salmon in B.C., but the cause of the lesion is unknown.