Cryopreservation of spotted halibut (Verasper variegatus) sperm

Spotted halibut (Verasper variegatus) is now regarded as being endangered in China because of its continuous decline in the last three decades. Preservation and protection of its genetic resources were demanded in order to protect this rare fish species. In this project, cryopreservation technique for sperm of spotted halibut was developed. The effects of various extenders and cryoprotectants on motility of frozen–thawed sperm were examined. The motility of frozen–thawed sperm in TS-2 was higher than that in ASW and MPRS (p < 0.05) and was not significantly different from that of fresh sperm (p > 0.05). While the motility of frozen–thawed sperm cryopreserved with 13.3% EG (ethylene glycol), 13.3% glycerol, 13.3% MeOH (methanol) and 13.3% DMF (dimethylformamide) was less than 5%, no significant differences were observed in the motility between fresh sperm and frozen–thawed sperm cryopreserved with 13.3% DMSO (dimethyl sulfoxide), 13.3% PG (propylene glycol) (p > 0.05). Using the above method, we cryopreserved spotted halibut semen with extender TS-2 and 13.3% DMSO or 13.3% PG. As a result, the fertilization rate (34.52 ± 10.92%) and hatching rate (23.53 ± 11.80%) of frozen–thawed sperm were not significantly different from that of fresh sperm (p > 0.05). Motility and time delay in the activation of frozen–thawed sperm activated by artificial seawater at different salinity were different. Low salinity (low osmolality) could delay the activation of frozen–thawed sperm. The highest motility was observed with artificial seawater of 30‰ (p < 0.05). The most suitable temperature of seawater to activate spotted halibut frozen sperm was determined to be 18 °C (p < 0.05). However, temperature of seawater has no significant effect on time delay in the activation of frozen–thawed sperm (p > 0.05).