Studies of a fatal pollutant-Induced hyperbilirubinemia in spawning Atlantic salmon

Freshly run adult Atlantic salmon (Salmo salar) returning to the River Don (Aberdeenshire, Scotland) show periodic epidemics of a fatal disease of the blood and liver, characterised by hyperbilirubinaemia, haemolytic anaemia and structural damage to the liver. Since previous studies have ruled out agents of infectious aetiology, attention has focused on the possible causative role of xenobiotics present in the River Don. In this study the activities of inducible biotransformation and detoxication systems, plasma and tissue components were investigated in farmed salmon, in wild salmon from the River Don and from the non-polluted River Esk, and in Esk salmon held in tanks containing water from a paper mill effluent, an effluent from an industrial drain or a mixture of the two. The results indicated that the diseased and many of the apparently healthy River Don salmon had induced mixed function oxygenase activities and metallothionein levels indicative of both organic and heavy metal pollutant impact. In fish exposed experimentally to paper mill effluents hepatic MT levels were not induced but effluents from industrial drains in the lower river induced MFO activities up to 35-fold. Bilirubinaemia was inducible by sequential exposure to the industrial drain effluent and effluent from the paper pulp mill, indicating that some aspects of the disease are due to synergistic pollutant effects.