RELATIONSHIP OF CADMIUM-INDUCED HYPOCALCEMIA WITH MORTALITY IN RAINBOW-TROUT (SALMO-GAIRDNERI) AND THE INFLUENCE OF TEMPERATURE ON TOXICITY

Cold-acclimated (6°C) rainbow trout, exposed to lethal concentrations of cadmium, survived longer than warm-acclimated (12 and 18°C) trout. Ten-day lethal thresholds indicated that cold-acclimated trout could also resist greater concentrations of cadmium. Calcium concentrations in the plasma of fish, exposed to 0.3 mg Cd/L, declined steadily during the period of exposure when subjected to five thermal regimes, different combinations of acclimation and experimental temperatures. The rate of decline in calcium concentrations was correlated with the rate of mortality. Survival times of 12°-acclimated trout subsequently exposed to cadmium at 6, 12, and 18°C were inversely dependent on temperature, whereas survival times of trout acclimated to 6, 12, and 18°C and subsequently exposed to cadmium at acclimation temperatures do not show the same temperature dependence. Survival times of 12 and 18°-acclimated and exposed fish were similar, indicating that temperature compensation may promote longer resistance of 18°-acclimated and exposed fish than when they are acclimated to 12°C and abruptly transferred and exposed to cadmium at 18°C. Symptoms of cadmium poisoning of the fish are consistent with the effects of extreme hypocalcemia and are similar to those reported in the literature for various fish. The decline of calcium concentrations in the plasma may be the direct cause of mortality.