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 degrees C min(-1), mean +/- SD from -5 to -55 degrees C) is a promising protocol for cryopreservation of Arctic char semen.