Effects of in vivo and in vitro zinc and cadmium treatment on sperm steroidogenesis of the African catfish (Clarias gairepinus)

Low-level pollution of aquatic ecosystems may decrease the fecundity of fish populations either indirectly via accumulation in the reproductive organs, or acting directly on sperm and ovum. The activity of highly active hydroxy steroid dehydrogenase (HSD) enzyme in fish sperm has been used as indicator of water contamination with zinc, cadmium or zinc + cadmium. Three groups of six male African catfish were fed from the sexually immature juvenile stage, with diet containing 1000 ppm zinc, cadmium or zinc + cadmium for 110 days and 20aHSD activity in milt of these fish were compared with six other control fish fed with normal diet. The 20aHSD enzyme activity was also measured in in vitro incubation of milt from six control fish with different concentrations (0, 0.1, 1, 3, 10, 30, 100, 1000 and 3000 ppm) of zinc, cadmium or zinc + cadmium. A very high 20a hydroxy steroid dehydrogenase enzyme activity was found in all sperm incubations of African catfish. This enzyme converts 17-hydroxy progesterone (17P) substrate to 17,20a-dihydroxy progesterone (1720aP) product and the rate of enzyme activity is related to substrate (17P) concentrations. Significant differences (P<0.05) in enzyme activity in converting 17P to 17,20aP were found between in vitro incubations of sperm with different concentrations of zinc, cadmium or zinc + cadmium and control group (0 ppm). Significant differences (P<0.05) in enzyme activity and 17,20aP production were found between fish fed with diet containing 1000 ppm zinc or cadmium and the group fed with diet containing 1000 ppm zinc + cadmium and control groups. The results showed that 20aHSD enzyme activities in fish sperm may be used as indicator of water contamination with heavy metals and their bioaccumulations in testis of aquatic animals.