REPRODUCTION OF FISH IN CONDITIONS DISADVANTAGEOUSLY ALTERED WITH THE SALTS OF ZINC AND COPPER
The study consisted of incubating the oocytes and of fertilised eggs of common carp and goldfish in different zinc and copper concentrations. Also guppies and goldfish were reared in various zinc concentrations, whereas carp were given zinc with feeds. Determinations were performed of an increase of mature oocyte fractions, percentage of normal hatched larvae, gonadotropin (GtH II) level and gonadosomatic (GSI) index. It was found that zinc concentration as low as 3 mg/l and copper concentration 0.2 mg/l decreased hatchability and increased fractions of larval deformations. It was also discovered that rearing of guppies and goldfish in the concentrations which did not inhibit growth nor increased mortality (1.0 and 2.5 mg/l respectively) could result in a statistically significant reduction of progeny number. In the case of goldfish reared in 2.5 mg/l zinc concentration, a significantly lower level of GtH II than in the control was found after 456 days in both sexes. This implies adverse effect of zinc on reproduction processes at the level of hypothalamus and pituitary gland.