Effect of extender composition and freezing rate on post‐thaw motility and fertility of Arctic char, Salvelinus alpinus (L.), spermatozoa

The effects of extender composition and freezing rate on motility and fertility of frozen‐thawed Arctic char, Salvelinus alpinus , spermatozoa were investigated. Three freezing rates, two semen diluents and three cryoprotectants were tested. Semen frozen in 0.3 mol L −1 glucose diluent with 10% methanol as a cryoprotectant or in a diluent described by Lahnsteiner with 10% N,N‐ dimethylacetamide (DMA) resulted in the highest sperm motility. Fertility was the highest for semen frozen in a glucose–methanol extender but was not significantly different than that for semen frozen in Lahnsteiner's diluent with 10% DMA. Dimethyl sulphoxide (DMSO) at 10% was a relatively ineffective cryoprotectant with either semen diluent. Semen frozen at 6 cm above the surface of liquid nitrogen resulted in a higher post‐thaw sperm motility and fertility than semen frozen at 5 cm. The addition of 7% fresh egg yolk to glucose diluent containing methanol or DMSO did not improve the fertility of frozen‐thawed spermatozoa. However, the addition of 7% fresh egg yolk to glucose–DMA extender significantly improved the fertilization percentages of frozen‐thawed spermatozoa. In conclusion, dilution of semen 1:3 in 0.3 mol L −1 glucose with 10% methanol and freezing 6 cm above the surface of liquid nitrogen (freezing rate of 40±8°C min −1 , mean±SD from −5 to −55°C) is a promising protocol for cryopreservation of Arctic char semen.