Influence of seasonal changes in water temperature on cadmium inducibility of hepatic and renal metallothionein in rainbow trout

Abstract

Changes in metallothionein (MT) levels in liver and kidney of juvenile rainbow trout ( Oncorhynchus mykiss) were followed for 8 months, as the water temperature was allowed to follow the natural temperature decrease in Tvären, a bay in the Baltic Sea. The temperature dropped from 15 °C to 2 °C during the experimental period. The liver and kidney were analysed for MT, zinc, copper and cadmium. Both the hepatic and renal MT levels were found to increase in the control group during the first 4 months of the experiment, as the water temperature dropped to 4 °C. Once the temperature had stabilized at 2 °C there was a noticeable decrease in both hepatic and renal MT levels. One group of fish was exposed to water-borne cadmium (100 μg Cd/litre) for the duration of the experiment. Cadmium accumulated in both liver and kidney, and reached the highest levels in the kidney. Exposure of the fish to cadmium resulted in marked elevations of kidney MT levels. In the liver the MT levels did not increase above the control levels as the temperature dropped to 2 °C after 6 months. However, once the temperature stabilized at 2 °C (after 8 months) the hepatic MT levels were significantly higher in cadmium-exposed fish than in the control fish.