Optimal sperm concentration in straws and final glucose concentration in extender are crucial for improving the cryopreservation protocol of salmonid spermatozoa

Ensuring the precise conditions during cryopreservation relies on constant sperm concentration in straws with constant cryoprotectant concentrations, which are essential for standardizing cryopreservation protocols. The aim of our study was to test the effect of different sperm concentrations in straws with constant extender concentration on sperm motility parameters of cryopreserved semen of brown trout (Salmo trutta m. fario), sea trout (Salmo trutta m. trutta), brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar). At the same time, the usefulness of different straw sizes (0.25 and 0.5 ml) for cryopreservation of the semen of these species was examined. Additionally, the effect of the final glucose concentration at a constant sperm concentration on post-thaw sperm motility was evaluated. The final sperm concentration in straws at a constant cryoprotectant concentration influenced the post-thaw sperm motility parameters of salmonids. The optimal sperm concentration with high post-thaw sperm motility was 2.0 x 10(9) spermatozoa ml(-1) for brook trout, 3.0 x 10(9) spermatozoa ml(-1) for brown trout and sea trout and 4.0 x 10(9) spermatozoa ml(-1) for Atlantic salmon. The use of 0.5 ml straws led to higher or similar values of post-thaw sperm motility than the 0.25 ml straws. The final glucose concentration of 0.15 M produced the highest results of sperm motility after cryopreservation for all tested species. Our results demonstrated that the influence of sperm concentration in straws on cryopreservation success is species-specific within salmonids. On the other hand, the effect of glucose concentration did not appear to be species-specific. In our opinion, standardization of the semen cryopreservation protocol presented in this study is a prerequisite for the development of a repeatable procedure and hence the future implementation of cryopreserved semen in hatchery practice.