Cryopreservation of Atlantic cod (Gadus morhua) sperm in large-volume straws: applications for commercial production and gene banking
In our study, we used a full factorial analysis of variance design to examine the effects of diluent [Mounib's sucrose-based diluent+hen's egg yolk (EY) and Hanks' balanced salt solution (HBSS)+EY], freezing rate (−2.5, −5.0 and −7.5 °C min−1) and thawing rate (2.5, 5.0 and 7.5 °C min−1) on motility and velocity of Atlantic cod sperm cryopreserved in 2.5 mL cryogenic straws. We found that post-thaw sperm performance was strongly influenced by the presence of higher-order interactions of the factors we tested. For all models broken down by diluent, the 2.5 °C min−1 thawing rate had the lowest sperm motility recovery index. Mounib's sucrose-based diluent+EY had the highest motility recovery index at all thawing rates. Mean per cent motility for fresh sperm (87.7±2.9%) was not significantly different than of sperm cryopreserved using Mounib's sucrose-based diluent+EY, frozen at −2.5 °C min−1 and thawed at 5.0 °C min−1 (77.1±2.9%). For Mounib's sucrose-based diluent+EY, velocity was significantly higher with sperm thawed at 7.5 °C min−1, than sperm thawed at 2.5 °C min−1, while thawing rate had no effect for HBSS+EY. Our findings have implications for cod mariculture and aiding in conservation efforts for a dominant marine fish species.