Catfish farming constitutes about 75% of total U.S. finfish aquaculture production, where the channel catfish, Ictalurus punctatus female × blue catfish, I. furcatus male hybrid accounts for >50% of the harvest. Current hatchery technology to produce hybrids is labor intensive and requires the sacrifice of males for in vitro fertilization. This is expensive and time-consuming, as blue catfish males take 4 to 7 years to mature. Sperm are then often of low quality/quantity and do not necessarily give high fertility and hatch. Therefore, paternal gametes should be used sparingly, using the minimum quantity of sperm for fertilization, while still maximizing offspring production. This is particularly the case when using cryopreserved cells, as each male’s sperm, whether frozen or in living gene banks, is in limited supply. The objectives were to (i) compare sperm swimming kinematics and health metrics before and after cryopreservation; (ii) determine minimum quantity of frozen-thawed sperm required to maximize hatching success; and (iii) decipher how early offspring development is affected when eggs are sired with fresh and frozen-thawed sperm. Sperm kinematics were evaluated by computer assisted sperm analysis, while health metrics (i.e., viability, oxidative stress, DNA fragmentation) were assessed using fluorescent imaging and flow cytometry. Over 2 spawning seasons, eggs from 19 females were collected and fertilized using cryopreserved sperm from 38 males at 10 sperm to egg ratios (range from 1.0×104 to 9.0×105 sperm per egg). Embryos were then incubated under common environmental conditions and growth performance documented over 40 days post-hatch.
Generally, sperm kinematic traits and health metrics decreased after cryopreservation (Fig 1A). Despite this, hatching success using cryopreserved sperm was high, but dependent on sperm to egg ratio. For instance, at ratios of 1.0×104 to 5.0×104 sperm per egg, hatch increased from 18.0% ± 8.5 to 43.9% ± 8.2 (Fig. 1B). Adding greater than 5.0×104 sperm per egg had no significant effect on hatching success. Preliminary analyses suggest cryopreservation will not impact offspring performance. These data improve understanding of frozen-thawed sperm quality and paternal effects for blue catfish to improve reproductive sustainability and reduce production costs.