Cryopreservation of rainbow trout (Oncorhynchus mykiss) sperm: Evaluation of cryomedia and protocol optimization

A substantial body of research has been dedicated to the cryopreservation of rainbow trout sperm. However, the observed discrepancies across studies and the variability in outcomes highlight the need to optimize freezing protocols. The objective of this study is to provide support for the development of standardized, efficient protocols for utilization in cryobanking applications and selective breeding programs. In pursuit of this objective, two consecutive experiments were conducted to evaluate the efficacy of six distinct cryopreservation media. In these media, 10 % dimethyl sulfoxide (DMSO) or 7.5-10 % methanol (MeOH) were combined with various extenders, including FF (FreezeFish), V2 (Stein and Bayrle), MCR (Modified Cortland), 0.3 G (0.3 M glucose), and 0.15 G (0.15 M glucose). Additionally, the impact of pH adjustment and antioxidant supplementation on the efficacy of the 0.15 G-MeOH medium was examined. The findings demonstrated that the highest post-thaw motility rates could be attained with the FF-DMSO or 0.15 G-MeOH medium, and the FF-DMSO medium offers significant protection against freeze-thaw-induced DNA fragmentation. While neither pH adjustment nor antioxidant supplementation to the 0.15 G-MeOH medium had a significant effect on post-thaw motility parameters, both modifications significantly improved the fertilization success. However, the concomitant application of these two modifications resulted in a dose-dependent decline in both sperm motility and fertility. In light of the findings, it was concluded that both FF-DMSO and modified 0.15 G-MeOH media, particularly those incorporating either alkaline pH or an antioxidant, are promising candidates for the effective cryopreservation of rainbow trout sperm in cryobanking applications.