Comparative analysis of sperm freezability of sex-reversed female brook trout and sex-reversed female rainbow trout semen

The aim of our study was to compare quality of fresh and cryopreserved semen of sex-reversed female rainbow trout and sex-reversed female brook trout. The effect of different final sperm concentrations in straws with a constant extender concentration and final glucose concentration on the sperm motility parameters of cryopreserved semen was tested. Furthermore, we examined the effect of post-thaw storage time on sperm motility parameters at optimal sperm and glucose concentrations. The effects of semen cryopreservation from sex-reversed female rainbow trout and sex-reversed female brook trout on sperm fertilizing ability at the sperm-to-egg ratios 500,000:1 and 1,000,000:1 after 0 and 60 min of post-thaw storage of semen were investigated. We have demonstrated that final sperm concentrations in straws as well as final glucose concentrations in extended semen influenced post-thaw sperm motility parameters in both species. The high post-thaw sperm motility was recorded for sperm concentrations within the range of 1.0-4.0 × 109 spermatozoa ml−1 for both species. Furthermore, the glucose concentration appeared to be very important for cryopreservation success and its effect was species-specific. The final glucose concentrations of 0.15 M and 0.19 M, for sex-reversed female rainbow trout and sex-reversed female brook trout, respectively, produced the highest results for sperm motility after cryopreservation. The post-thaw sperm motility was unaffected by 60 and 360 min after thawing for sex-reversed female rainbow trout and sex-reversed female brook trout, respectively. The fertilization rates of cryopreserved semen of sex-reversed female rainbow trout were high and did not differ between the investigated sperm:egg ratios after 0 and 60 min of post-thaw storage. However, fertilization rates of cryopreserved semen of sex-reversed females brook trout were lower and decreased after 60 min of post-thaw storage of semen at sperm: egg ratio 1,000,000:1. In conclusion, our results demonstrated differences in freezability between the semen of sex-reversed female rainbow trout and sex-reversed female brook trout. The semen of both species can be cryopreserved at the final sperm concentration of 3.0 × 109 spermatozoa ml−1. However, the influence of final glucose concentration on cryopreservation success, as well as the duration of post-thaw storage time and fertilization rates, are species-specific. In our opinion, standardizing the procedure of semen cryopreservation presented in this study is a prerequisite for the development of repeatable procedures and the future implementation of cryopreserved semen from sex-reversed females into hatchery practice.