Cadmium toxicity to rainbow trout Oncorhynchus mykiss Walbaum and brown trout Salmo trutta L. over extended exposure periods.

The toxicity of cadmium in water is well known, but there have been few reports on the long-term effects of this metal on fish at concentrations near the European inland water standard of 5 micrograms Cd liter-1. This paper describes experiments in which adult rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta were exposed to cadmium concentrations near water quality standard levels for periods of up to 90 weeks. The survival and growth of these fish were assessed, and sperm and eggs were stripped from them to conduct early-life-stage tests. Continuous exposure of rainbow trout adults to cadmium concentrations of up to 5.5 micrograms Cd liter-1 did not affect their survival or growth. However, eggs obtained from rainbow trout exposed to 1.8 and 3.4 micrograms Cd liter-1 failed to develop to the fry stage. Oogenesis appeared to be delayed in brown trout exposed to 9.3 and 29.1 micrograms Cd liter-1, but the eggs and fry that were produced developed normally after fertilization. Adult brown trout suffered considerable mortality in the 29.1 micrograms Cd liter-1 treatment, with a median period of survival of 54 weeks.