Impact of sperm density on hatching success for channel catfish (Ictalurus punctatus) male × blue catfish (Ictalurus furcatus) female hybrid production

Authors: MYERS, JAELEN - Auburn University; NICHOLS, ZOE - Auburn University; ABUALREESH, MUYASSAR - Auburn University; HUSSEINI, NOUR - Auburn University; TAYLOR, ZACHARY - Auburn University; COOGAN, MICHAEL - Auburn University; GURBATOW, JEREMY - Auburn University; MINH, KHOI - Auburn University; ZADMAJID, VAHID - King Abdulaziz University; Chatakondi, Nagaraj; DUNHAM, REX - Auburn University; BUTTS, IAN - Auburn University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2020
Publication Date: 1/30/2020
Citation: Myers, J., Nichols, Z., Abualreesh, M., Husseini, N., Taylor, Z., Coogan, M., Gurbatow, J., Minh, K., Zadmajid, V., Chatakondi, N.G., Dunham, R., Butts, I. 2020. Impact of sperm density on hatching success for channel catfish (Ictalurus punctatus) male × blue catfish (Ictalurus furcatus) female hybrid production. Aquaculture. 521:735024.

Interpretive Summary: Hybrid catfish fry are reliably produced in catfish hatcheries to meet the needs of the US farm-raised catfish industry. Even though hybrid catfish fry production is increasing in hatcheries, inefficiencies still exist in hatchery production that needs to be identified and addressed. Determining optimizing gamete ratio in the artificial fertilization production protocol is an essential step to maximize the efficiency of hatchery production. Hatching trials were conducted to fertilize eggs from 9 strip-spawned Channel catfish females in two locations fertilized with six sperm to egg ratios. Milt from 3 males were pooled to arrive at 6 pre-determined ratios to fertilize stripped eggs in four replicates per ratio under controlled hatching conditions in the following ratios: 100,000, 50,000, 25,000,10,000, 5,000, and 1,000: 1. The goal was to determine the minimum number of sperm to fertilize an egg to maximize hatching success. Based on two hatching trials, optimal ratio of blue catfish sperm to egg was 10,000 : 1 to maximize hybrid catfish embryo production efficiency. Implementing this sperm to egg ratio in commercial hatcheries will likely fertilize 7,000 to 10,000 eggs per mL, an increase of 7 to 10 folds of current levels fertilized in hatcheries. Findings suggest, US catfish industry can utilize lower sperm to egg ratio for consistent and efficient hybrid catfish fry production in hatcheries while conserving blue catfish males and their precious gamete resources.

Technical Abstract: Hybrid catfish, the progeny of channel catfish (Ictalurus punctatus) females X blue catfish (I. furcatus) males, are in high demand by the aquaculture industry due to their superiority for pond and raceway culture in the United States. 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. Therefore, it is essential to efficiently utilize gamete resources by using the minimum quantity of sperm that allows for the highest fry production from these valuable males. In this study, channel catfish eggs from 9 females were collected from two study different locations and fertilized with 6 different sperm to egg ratios ranging from 1,000 to 100,00 sperm :1. Embryos were then incubated under common environmental conditions until hatch. Average hatch success for the 9 females, using sperm to egg ratios between 1,000 and 100,000 sperm per egg ranged from 18.3% to 48.8%. Hatch for the lowest performing female ranged from 0% to 12.5%, while the highest ranged from 22.7 to 81.9% with much greater variability due to sperm density. Overall, there was a significant effect of sperm to egg ratio (P < 0.0001), such that hatch success increased from 5,000 sperm per egg to 10,000 sperm per egg. Thereafter, adding more than 10,000 sperm per egg had no significant improvement on hatch success. Independently, both study locations indicated significant impacts of sperm to egg ratio (P < 0.0001) 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 10,000 sperm per egg yielded no increase in hatch, while this density threshold was lower for location 2, where no improvement at ratios higher than 5,000 sperm per egg 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 for fry production. Based on these findings, we suggest that implementing the 10,000 sperm to egg ratio will standardize hatch success for hybrid catfish production, while conservatively using the least amount of sperm and maximizing the hatching capacity for each blue catfish male.