Cryopreservation of channel catfish sperm: effects of cryoprotectant exposure time, cooling rate, thawing conditions, and male-to-male variation.

The purpose of this study was to extend previous work on the cryopreservation of channel catfish (Ictalurus punctatus) sperm. The objectives were to compare the effects of freezing and thawing on motility of sperm for: (1) 1 or 48-h exposure before freezing to 5% methanol and use of 0.5 or 0.25 mL straws; (2) 1 h or 5-day exposure before freezing to 5% methanol; (3) cooling at 45 or 3 degrees C/min; (4) thawing at 30, 40 or 50 degrees C using 5 or 10 s duration, and (5) cryopreservation with 5 or 10% methanol of samples from 50 males to analyze male-to-male variation. No differences were found in motility reduction for 1 or 48 h exposure times in 5% methanol, for use of 0.5 or 0.25 mL straws, or for 1 h or 5-day exposures in 5% methanol. A cooling rate of 45 degrees C/min resulted in lower motility reduction (33+/-9%) than a rate of 3 degrees C/min (83+/-13%) (P=0.002). A thawing temperature of 50 degrees C resulted in lower motility reduction (25+/-14%) than 30 degrees C (51+/-21%) or 40 degrees C (59+/-11%) (P=0.001). A thawing duration of 10 s resulted in lower motility reduction (38+/-12%) than a duration of 5 s (52+/-12%) (P=0.005), and there was an interaction between thawing temperature and duration (P=0.050). A concentration of 5% methanol resulted in lower motility reduction (43+/-17%) than 10% methanol (67+/-14%) (P=0.001). Regression analysis showed no relationship between motility before freezing and after thawing for 5% methanol (r2=0.012) or 10% methanol (r2=0.011).