Application of glucose–methanol extender to cryopreservation of semen of sex-reversed females rainbow trout results in high post-thaw sperm motility and fertilizing ability

• Semen of rainbow trout neomales was effectively cryopreserved with glucose-methanol
• The post-thaw sperm fertilization ability was similar to that of fresh semen
• The post-thaw sperm viability was well correlated with fertilization ability

We tested the usefulness of 0.18 M glucose in 9% methanol as an extender for the cryopreservation of semen of sex-reversed rainbow trout females (n = 9). The semen-to-extender ratio of 1:9 and 15 min equilibration were used. Motility and viability parameters as well as the fertilization rate at the eyed stage and hatching were assessed for post-thaw sperm. The fertilization success of cryopreserved semen was about 80% for both 500,000 and 1,000,000:1 sperm-to-egg ratios. The application of the cryopreservation procedure resulted in remarkably high post-thaw sperm motility and viability (55 and 56%, respectively). Our results for the first time show that the post-thaw fertilization ability of rainbow trout sex-reversed female semen can be similar to that of fresh semen at a sperm-to-egg ratio as low as 500,000:1. The sperm motility pattern characterized by low linearity, high amplitude of lateral head displacement and curvilinear velocity seems to be beneficial for the fertilizing ability of thawed sperm. Sperm viability appears to be a reliable indicator of the quality of thawed semen of rainbow trout sex-reversed females. The cryopreservation procedure using glucose–methanol extender after scaling up can be recommended for routine hatchery practice.