Gamete Quality and Reproductive Performance in Clarias gariepinus   Chronically Exposed to Industrial Effluent Mixtures

Clarias gariepinus fingerlings were raised to adulthood for nine months in sublethal concentrations (7.67%, 3.83%, 2.56% and 1.92%) of binary mixtures (75:25%) food:beverage effluents and an unexposed control group in a static/renewal bioassay to investigate the effects of industrial effluent on gamete quality and progeny survival. Body weight and GSI of female broodstock were determined. Gamete qualities were also evaluated. To determine reproductive outcomes and larval survival, half of the stripped eggs of female broodstock from all exposure groups were fertilized with milt of males from control exposures in the first experimental setup while for the second experimental setup, the other half of exposed female eggs were fertilized with milt from male broodstock from the same exposure concentrations. Significant concentration dependent decreases were recorded in broodstock body weight, sperm motility and milt volume, egg weight and diameter in all experimental exposures compared with control. Significant concentration dependent decreases were also recorded in hatching period, total number of hatched eggs, % egg viability and larval survival at 21 days. The observed decreases in gamete indices are consistent with lower reproductive outcomes and poor larval survival in higher exposure concentrations, and may influence recruitment and population growth in natural environments.

Keywords
gamete quality; industrial effluents; hatching success; Clarias gariepinus