Cryopreservation of the sperm of spotted halibut Verasper variegates (Pleuronectiformes, Pleuronectidae)

Abstract

The sperm of spotted halibut Verasper variegates was cryopreserved by a simple and convenient protocol. The cryoprotectants used were dimethyl sulfoxide (Me₂SO), glycerol (Gly), methanol (MeOH), Me₂SO + egg yolk, Gly + egg yolk and MeOH + egg yolk. The percentage of forward motile sperm in semen cryopreserved in the different extenders with Me₂SO, Gly, MeOH, Me₂SO + egg yolk, Gly + egg yolk and MeOH + egg yolk was 40.5 ± 4.2%, 49.5 ± 4.2%, 38.3 ± 2.4%, 65.0 ± 4.0%, 67.5 ± 2.9% and 49.5 ± 8.4%, respectively. The fertilization and hatching rates of cryopreserved sperm were from 59 ± 2.4% to 70 ± 3.0%, and from 11 ± 3.0% to 18 ± 2.6%, respectively. These tended to be highest when Gly + egg yolk or Me₂SO + egg yolk were used as cryoprotectants. Under SEM, it could be seen that while the majority of the freeze-thawed sperm remained morphologically normal, some exhibited damaged or lost mitochondria, which possibly caused the decrease in motility and fertility of the freeze-thawed sperm