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-= -13.19x2-+-55.90x-+-38.44, r2=0.823) and the optimum range of sperm-:-egg ratios was between 1.379×106 and 2.758×106. When sperm were cooled for 5-min with 5% methanol, fertilization rate was linearly related to sperm-:-egg ratio (y=22.51x-+-23.26, r2=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=-29.65x2-+-119.2x---51.04, r2=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.
ASJC Scopus subject areas
- Aquatic Science