The effects of extenders and sperm‐egg ratios on fertilizing ability of cryopreserved testicular sperm of northern pike (Esox lucius L.)

The effects of four different extenders and two sperm‐to‐egg ratios on fertilizing ability of cryopreserved testicular sperm of northern pike (Esox lucius L.) were tested in the present study. Testicular sperm was diluted with each of the four extenders (0.6 m sucrose + 15% DMSO, 0.3 m glucose + 15% DMSO, 0.6 m sucrose + 10% methanol and 0.3 m glucose + 10% methanol, all supplemented with 10% egg yolk and 1.7 g KCl L^?1) and frozen in 0.5‐ml straws at 2 cm above the surface of liquid nitrogen and thawed at 25°C for 30 s. Then 125 μl or 50 μl of frozen‐thawed testicular sperm was poured onto about 1250 eggs for fertilization. The results showed that both sperm‐to‐egg ratio and diluent had no significant influence on cryopreservation efficiency of testicular sperm, whereas cryoprotectant had a significant influence. The highest fertilization rate (92.2%) was obtained from testicular sperm cryopreserved in glucose‐based extender containing 10% methanol at a sperm‐to‐egg ratio of 1 × 10⁶ spermatozoa per egg. The results indicated that glucose‐based extender containing 10% methanol, 10% egg yolk and 1.7 g KCl L^?1 was a useful combination.