INVOLVEMENT OF CORTISOL AND METALLOTHIONEIN-LIKE PROTEINS IN THE PHYSIOLOGICAL-RESPONSES OF TILAPIA (OREOCHROMIS-MOSSAMBICUS) TO SUBLETHAL CADMIUM STRESS

Exposure of freshwater tilapia to a sublethal cadmium concentration in the water (10 μg Cd/l) induced a rapid elevation (within 1 h) of plasma cortisol levels. Concentrations remained increased for at least 4 days during which time hypocalcemia, hyponatremia and hyperglycemia were observed; concurrently the opercular chloride cell density doubled. After this time, cortisol levels gradually decreased, plasma cadmium, natrium and glucose returned to (near) normal levels while a concomitant rise in the metallothionein-like protein content of gill, kidney and liver was observed. We conclude that, in tilapia, cortisol, by initiating physiological responses and via possible synergism with other hormones like prolactin, enables the fish to counter-act the adverse effects of Cd. This hormonal response apparently forms an intrinsic part of a general adaptation response of fish to sublethal Cd-stress. © 1990.