Optimization of conditions for the cryopreservation of yellow catfish (Pelteobagrus fulvidraco) sperm

Yellow catfish (Pelteobagrus fulvidraco) is a promising aquaculture species in China with an increasing market demand. To serve the growing demand of male broodstock for artificial fertilization and the preservation of valuable strains for selective breeding, we tried to develop a species-specific cryopreservation protocol for yellow catfish sperm in this study. Important factors such as cryoprotectant, freezing height above the liquid nitrogen (LN) surface, dilution ratio, equilibration time, thawing temperature and cool storage before freezing were standardized. Among the cryoprotectants tested here, 10% Me2SO was the most suitable for sperm cryopreservation. Freezing at 7 cm above the LN surface for 10 min yielded the highest post-thaw motility. Further evaluation showed that dilution ratio of 1:3 and 1:5 produced higher post-thaw motility than semen diluted at 2:1, 1:1, 1:9 or 1:19. Equilibration times from 0 to 30 min did not cause significant differences in both equilibrated and post-thaw motility. Also, cool storage up to 24 h did not affect the suitability of sperm for cryopreservation. After thawing, sperm could be stored at 4 °C for 2 h without a reduction in motility parameters. With the combination of optimized freezing conditions, the fertilization and hatching rate of cryopreserved sperm were 87.1 ± 5.2% and 78.5 ± 7.4%, respectively, which were similar to those of fresh sperm (91.8 ± 3.5% and 83.7 ± 2.5%). In general, the cryopreservation protocol optimized here would facilitate breeding practice and hatchery operation in this economically important fish.