Abstract
In the case of artificial fertilization practiced in salmonids, rinsing of unfertilized eggs with an isotonic solution (ISER), consisting of 154.7mM NaCl, 3.2mM KCl and 2.3mM CaCl2, has been widely used to avoid contamination of the yolk from broken eggs which often causes infertility of the spermatozoa. Experiments were carried out in the masu salmon Onchorhynchus masou to determine the effect of osmolality and ionic composition of the solution on sperm motility. In ISER, duration of sperm motility was about 6 and 2.5-3 times longer than that in distilled water and isotonic NaCl or CaCl2 solutions, respectively. The maximum duration of sperm motility was obtained in the isotonic condition (300mOsm/kg) when the semen was dilated with solutions of the same ionic composition as ISER. A complete lack of either NaCl or CaCl2 from the isotonic solution resulted in a significant decrease in sperm motility, but that of KCl did not affect the motility. Duration of sperm motility was prolonged successfully in varying mix-tures of NaCl and CaCl2 of the constant osmalality at 300mOsm/kg in the range from 1 to 50mM CaCl2. It is concluded that the isotonic solution of NaCl with 1-30mM CaCl2 is fully efficient as a sperm diluent for the masu salmon, and that the addition of KCl is not necessarily essential for the diluent.
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