Effect of pH and cation concentrations on spermatozoan motility of sea trout (Salmo trutta m. trutta L.)

Environmental conditions during external fertilization in fish have a significant effect on spermatozoan motility (MOT) and fertilization ability. Even in the same family of fish, spermatozoa might differ in sensitivity to ions present in the external medium. Elucidation of such differences within a species would help to understand spermatozoan biology and to determine external conditions that would optimize spermatozoan MOT and successful fertilization. Objectives of the current study were to determine the effects of pH and of sodium, potassium, and calcium ion concentrations in the activation solution on sea trout spermatozoan MOT. Six parameters characterizing MOT (MOT, curvilinear velocity [VCL], linearity, amplitude of lateral head displacement, beat cross frequency, and duration of MOT) in spermatozoa activated in prepared buffers were traced by computer-assisted sperm analysis. Sea trout spermatozoa were motile over a wide range of pH values, and increasing pH did influence MOT, VCL, linearity, amplitude of lateral head displacement, and MOT duration. The optimum pH for sperm MOT was established at approximately 10. Increasing K+ ion concentration within the observed range caused a decrease in MOT and VCL. Spermatozoan movement ceased at 8 mM KCl concentrations. In Ca2+ buffers, sperm were motile within the range of 0 to 70 mM CaCl2 concentration; although beyond 8 mM concentration, VCL and MOT gradually declined. Spermatozoan aggregation was observed at the highest ion concentrations tested. Increasing CaCl2 concentration affected MOT pattern from initiation to termination of spermatozoan movement in a similar manner as changes associated with increasing pH. At concentrations of CaCl2 higher than 0.5 mM and in buffers with pH values 10 to 11, movement of spermatozoa was characterized by high initial linearity followed by its gradual reduction. In contrast to the effects of KCl and CaCl2, increasing NaCl concentration up to 90 mM Na+ concentration prolonged the duration of spermatozoan movement and, up to 60 mM Na+ concentration, slightly increased sperm velocity as well. Above the concentration of 90 mM NaCl, these parameters decreased; and at 240 mM of Na+, spermatozoa did not activate.