Impact of of sperm density on hatch success for channel catfish (Ictalurus punctatus) ♀ x blue catfish (Ictalurus furcatus) ♂ hybrid production

Hybrid catfish, the progeny of channel catfish (Ictalurus punctatus) females x blue catfish (I. furcatus) males, are in high demand by the United States aquaculture industry because they outcompete each of the parent species for pond and raceway culture. Unfortunately, fry production can be a limiting factor due to a lack of natural hybridization between the two species and the necessity to sacrifice males for artificial fertilization. Males are costly to maintain in hatcheries and take longer to mature than channel catfish males. Therefore, it is essential to use the minimum quantity of sperm that allows for the highest fry production. In this study, channel catfish eggs from 9 females were collected from two different locations and fertilized with six different sperm to egg ratios ranging from 1.0 x 10(3):1 to 1.0 x 10(5):1. Embryos were then incubated under common environmental conditions until hatch. Overall average hatch success +/- SE using sperm to egg ratios between 1 x 10(3) and 1.0 x 10(5) ranged from 18.3 +/- 4.3 to 48.8 +/- 8.3%. Overall, there was a significant effect of sperm to egg ratio (P < .0001), where hatch success increased from 5 x 10(3):1 to 1 x 10(4):1 sperm per egg. Thereafter, adding > 1 x 10(4):1 sperm per egg had no significant improvement on hatch success. Both study locations indicated significant impacts of sperm to egg ratio (P < .0001) on hatch success, which ranged from 18.2% to 57.3% at location 1 and from 18.6% to 32.3% at location 2. For location 1, ratios higher than 1 x 10(4):1 sperm per egg yielded no increase in hatch. This density threshold was lower for location 2, where no improvement at ratios higher than 5 x 10(3):1 were detected. Thus, lower sperm densities may be optimal under certain conditions. Maternal effects were responsible for up to 93.6% of the hatch variability, indicating the importance of individual females and egg quality for fry production. Based on these findings, we suggest that implementing the 1.0 x 10(4):1 sperm to egg ratio will support the standardization of in vitro fertilization methodologies for hybrid catfish production. Simultaneously, sperm economy and hatch capacity can be maximized for each blue catfish male.