A series of three experiments was carried out to investigate factors that affect the fertility of frozen-thawed rainbow trout sperm. (1) The concentration of DMSO added to the extender was varied from 5 to 20 ml/100 ml extender and simultaneously the sperm were equilibrated in these extenders for less than 1, 2, 4 and 60 min at 0°C. (2) The suitability of sucrose (0, 100, 200 or 300 mmol) and KCl (0, 6.7, 13.4, 20.2, 26.9 or 33.6 mmol) as extender components was tested. (3) By varying the concentration of the thawing solution (NaHCO3), the effect of osmotic pressure in the thawed sperm-thawing solution suspension was investigated. DMSO concentrations between 10% and 20% provided high post-thaw fertility (77%) when sperm equilibration time was kept at a minimum. With increasing DMSO concentration, the detrimental effect of any equilibration time was more pronounced. Sucrose did not influence the fertility of cryopreserved sperm in the presence of KCl. The use of 6.7 mmol KCl showed a slight advantage over KCl-free extenders. The absence of sucrose and KCl resulted in reduced sperm survival. Sperm thawed in solutions of different ionic strength had the highest fertility (85%) at the lowest osmolality tested (249 mOsm). Fertility dropped significantly with increasing osmolality to a lowest level of 61% at 365 mOsm. © 1983.
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