Efficient method for cryopreservation of European huchen (Hucho hucho L.) and grayling (Thymallus thymallus L.) semen

The objective of this study was to test the effect of cryopreservation with the use of a methanol-glucose extender on sperm motility parameters and fertilization rates of European huchen (Hucho hucho) and grayling (Thymallus thymallus), belonging to the Salmonidae family of Salmoniformes. Distinct differences between those species in absolute fertilization rates, sperm concentrations and sperm motility parameters were noticed. Post-thaw sperm motility of huchen was low (about 45%) compared to sperm motility of cryopreserved grayling semen (about 68%). Absolute fertilization rates of cryopreserved huchen semen were high: 87-88% of eyed embryos and 75-80% of hatched larvae. On the other hand, absolute fertilization rates of cryopreserved grayling semen were low (about 50%), but the relative fertilization rates amounted to 100% of control with fresh semen. To the best of our knowledge, this study is the first report to demonstrate that the post-thaw fertilization rate of semen can be comparable to that of fresh semen at a ratio as low as 1.5 × 105 and 5 × 105 spermatozoa per egg for grayling and huchen, respectively. The described method seems to be universal for the cryopreservation of semen of Salmonidae. In our opinion, it can be a very useful tool for ongoing efforts for conservation of European huchen and grayling in Central Europe, for aquaculture of those species, as well as this procedure can be implemented in hatchery conditions after scaling-up.