Cryopreservation of paddlefish sperm in 5-mL straws

Abstract

Summary Experiments were conducted to test the feasibility of using 5-mL straws for the cryopreservation of paddlefish (Polyodon spathula) sperm. In experiment 1, the effects of 5% or 10% methanol as a cryoprotectant in combination with cooling times of 5 or 7 min on paddlefish sperm stored in 5-mL straws were evaluated for fertilization and hatching rates. Highest fertilization rate of 48 ± 5% (mean ± SE) and hatching rate of 47 ± 10% were observed using sperm cryopreserved with 5% methanol and a 5-min cooling time in liquid nitrogen vapors. However, fertilization and hatching rates were significantly lower with cryopreserved sperm than with fresh sperm (fertilization 77 ± 6%; hatching 66 ± 13%). In experiment 2, the effects of sperm : egg ratios on fertilization rates were investigated. When fresh sperm was used, fertilization rate was quadratically related to sperm : egg ratio (y = )13.19x 2 + 55.90x + 38.44, r 2 = 0.823) and the optimum range of sperm : egg ratios was between 1.379 · 10 6 and 2.758 · 10 6 . When sperm were cooled for 5 min with 5% methanol, fertilization rate was linearly related to sperm : egg ratio (y = 22.51x + 23.26, r 2 = 0.75) but optimum sperm : egg ratio was not reached. In experiment 3, the hatching rates were not significantly different between the three-straw treatment and the control. With cryopreserved sperm, the relationship between the sperm and egg ratios and the hatching rates were best described by a quadratic equation (y = )29.65x 2 + 119.2x ) 51.04, r 2 = 0.837). Therefore, when cryopreserved sperm is used, sperm : egg ratio should be increased significantly to optimize fertilization and hatching rates. This can be achieved either by increasing the total volume of cryopreserved sperm by at least 30% or by further research to improve the procedure to increase the viability of post-thawed sperm per straw.