Physiological functions of osmolality and calcium ions on the initiation of sperm motility and swimming performance in redside dace, Clinostomus elongatus

Reproductive potential of fish stocks is critically dependent on sperm performance in an aquatic environment. The aim of this study is to test hypotheses, which govern the initiation of sperm motility and swimming performance, through physiological functions of osmolality and Ca2 + ion, in a threatened species of freshwater fish, the redside dace, Clinostomus elongatus. Spermatozoa motility was activated in either ionic or non-ionic media spanning a range of osmolalities. The role of Ca2 + channels on induction of spermatozoa motility and velocity was experimentally investigated by diluting sperm in media that contain various Ca2 + channel blockers. Results show that initiation of spermatozoa motility is a hypo-osmolality dependent mechanism. Inhibitors for L-type Ca2 + channels partially prohibited initiation of spermatozoa motility, while velocity was significantly reduced in both L-type and T-type Ca2 + channel blockers. Examination using W-7, an inhibitor for Ca2 +-dependent calmodulin, showed significant decreases in spermatozoa motility and velocity. Involvement for Ca2 + in axonemal beating was confirmed by significant increases in velocity after adding Ca2 + into the activation media, while motility remained unchanged in Ca2 + supplemented activation media. Together, these findings suggest the involvement of Ca2 + in hypo-osmolality-dependent initiation of spermatozoa motility mediated by activation of Ca2 + binding protein in the axoneme of a freshwater fish sperm. Blocking Ca2 + exchange through L- or T-type Ca2 + channel influences flagellar beating force and leads to decrease in spermatozoa velocity.