Sublethal effects in Atlantic salmon (Salmo salar) exposed to mixtures of copper, aluminium and gamma radiation

The present study was designed to investigate the effects in presmolt of Atlantic salmon (Salmo salar) exposed to copper (Cu), aluminium (Al) and gamma radiation, individually or in combination. Fish were exposed for 48 h to metals added to lake water; 10, 40 and 80 μg Cu/L, 250 μg Al/L and a combination of 40 μg Cu/L and 250 μg Al/L. In addition, gamma radiation (4–70 mGy delivered over 48 h) was added as an additional exposure stressor. Selected endpoints were chosen to reveal different toxic mechanisms and included Cu and Al accumulation on gills, blood chemistry and haematological variables (plasma sodium and chloride, haematocrit, glucose), hepatic levels of reduced and oxidised glutathione (GSH and GSSG) and hepatic transcriptional response of glutathione peroxidase (GPx), gamma-glutamylcysteine synthetase (GCS), metallothionein (MT) and ubiquitin. Exposure to Cu alone resulted in gill accumulation of Cu, reduction of plasma ions and increased transcriptional response of GPx, MT and ubiquitin. Exposure to Al alone reduced plasma ion levels but did not affect any of the hepatic biomarkers except for ubiquitin. The combined metal exposure (Cu + Al) altered the GSH levels, however GPx and MT were not affected suggesting a different mode of detoxification in the combined exposure. Gamma radiation appeared to influence GSH and ubiquitin levels. The observed effects seemed to be both stressor and concentration dependent.