Effect of tributyltin on adenylate content and enzyme activities of teleost sperm: a biochemical approach to study the mechanisms of toxicant reduced spermatozoa motility.

The effects of tributyltin (TBT) on the energy metabolism and motility of fish spermatozoa were investigated in vitro in African catfish and common carp. A significant (P<0.05) decrease of the duration and the intensity of motility was observed in catfish spermatozoa exposed to 0.27 microg/l TBT for 24 h. Exposure of catfish spermatozoa to 2.7-27 microg/l TBT caused an instant decrease in ATP content. In the presence of 27 microg/l TBT approximately 55% of the initial ATP concentration in catfish semen was lost after 60 min incubation while AMP concentrations increased and the total adenine nucleotide (TAN) pool remained unchanged. The reduction in sperm ATP levels could not be attributed to cell death since viability decreased only slightly over the period of exposure. In carp by contrast, none of the adenylates concentrations studied (ATP, ADP and AMP) were affected by TBT exposure at any experimental condition. However, carp sperm motility was significantly reduced by exposure to 2.7 microg/l TBT. Among the enzymes investigated only lactate dehydrogenase (LDH) in catfish sperm was significantly (P<0.01) affected by 27 microg/l TBT treatment with a reduction in activity of approximately 75%. Compared with carp sperm before TBT exposure, that of catfish had lower adenylate contents and overall lower enzymatic activities; this explains its slower sperm velocity and shorter duration of movement as measured by computer assisted sperm analysis (CASA). The present in vitro study shows that catfish spermatozoa are more sensitive to TBT exposure (and probably to other toxicants) than those of carp.