Effect of mercuric chloride and cadmium chloride on gonadal function and its regulation in sexually mature common carp Cyprinus carpio.

Gonadal function in fish, Cyprinus carpio was significantly affected by sublethal doses of mercuric chloride (HgCl2) and cadmium chloride (CdCl2) in chronic (45 days) exposure. Parameters investigated were nonesterified (NE) and esterified (E) cholesterol of ovary, liver and serum and ovarian 3 beta-Hydroxysteroid and 17 beta-Hydroxysteroid dehydrogenase enzyme activity and serum and pituitary gonadotropin (GtH) levels. Both the pollutants were able to reduce the hypothalamic extract (HE) or gonadotropin releasing hormone (GnRH) induced pituitary GtH release in vitro. Short term (96h) exposure of the fish to the pollutants had no significant effect on the gonadal function. In addition to the deleterious effect of pollutants on the gonadal steroidogenesis and pituitary gonadotropin release, using [4-14C] cholesterol as a tracer it was found that for 45 days exposure, HgCl2 had an adverse effect on the transport of cholesterol from circulation to ovary.