Cryopreservation of semen from the endangered Caspian brown trout (Salmo trutta caspius)

Semen cryopreservation of the endangered Caspian brown trout (Salmo trutta caspius) and effects of two extenders and three thawing rates on fertilizing ability were studied. After assessment of semen quality, one part of semen was diluted with three parts of extender and filled into 0.5-ml straws. Freezing was carried out at 2 cm above surface of liquid nitrogen and thawed at 5 °C for 90 s, 15 °C for 45 s and 25 °C for 30 s in water baths and used for fertilization. Use of the extender: 0.3 M glucose + 10% methanol + 10% egg yolk, and 0.6 M sucrose + 10% DMSO + 10% egg yolk, yielded 66.6% ± 2.2 and 59.8% ± 5.1 eyeing rates, respectively. Thawing of cryopreserved semen was best at 25 °C water bath for 30 s and significant differences were seen in the eyeing and hatching rates between 25 °C water bath with 5 °C, 15 °C (p < 0.05). Significant interactions (p < 0.05) were found between extender type and thawing rate in this study.