Osmolality and potassium ion: their roles in initiation of sperm motility in teleosts.

Spermatozoa that are quiescent in electrolyte and nonelectrolyte solutions isotonic to seminal plasma show motility when the semen is diluted with hypotonic solution in freshwater teleosts (four species tested) and with hypertonic solution in marine teleosts (five species tested). Decrease or increase, respectively, in osmolality of the environment may be the factor initiating sperm motility in these species. The motility of chum salmon spermatozoa in a sodium chloride solution isotonic to seminal plasma is completely suppressed by approximately 10 millimoles of potassium per kilogram; topminnow spermatozoa, however, were immotile in a nonelectrolyte solution, and motility was induced by electrolytes, especially potassium. Thus ions, rather than osmolality, may be an essential determinant of sperm motility in salmonid and viviparous teleosts.