The effects of extender type, freezing and thawing rates on fertility of the cryopreserved semen of the Caspian brown trout (Salmo trutta caspius )

Cryopreservation of semen from the Caspian brown trout (Salmo trutta caspius) and effects of extender type, freezing and thawing rates on fertilization ability were studied. After assessment of semen quality, one part of semen was diluted with three parts of different extender and decanted into 0.5ml straws. Freezing was carried out at two freezing levels, 1.5cm and 2cm above surface of liquid nitrogen. The semen was thawed at 5&deg;C for 90s, 15&deg;C for 45s or 25&deg;C for 30s in water baths and used for fertilization. Using the extender: 0.3 M glucose+10% methanol+10% egg yolk, and 0.6 M sucrose 10% DMSO + 10% egg yolk, yielded the highest post-thaw fertilization rates, with 67.05%&plusmn;8.76 and 59.78%&plusmn;5.08 eyeing rates, respectively. No significant differences were found in the fertilization rates with two freezing levels (P>0.05), however eyeing and hatching rates were higher for 2cm above the surface of the liquid nitrogen than for 1.5cm. Thawing of cryopreserved semen was best using the 25&deg;C water bath for 30s and significant differences were seen in the eyeing rates between 25&deg;C and 5&deg;C or 15&deg;C (P<0.05). Significant interactions (P<0.05) were found between effects of extender type and thawing rates and extender type and freezing rates.