Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2003
Publication Date: 9/1/2004
Citation: Genetic effects for growth and resistance to Edwardsiella ictaluri estimated from a diallel cross among USDA-102 strain channel catfish Ictalurus punctatus, blue catfish Ictalurus furcatus, and their F1 hybrid. Journal of the World Aquaculture Society 35:418-424. 2004 Interpretive Summary: Offspring from crosses among species or breeds may exhibit improved performance relative to the performance of their parents. The improved performance, or hybrid vigor, has been used to improve production efficiency in livestock and crops and may be useful for improving production of farm-raised catfish. The purpose of this study was to determine the genetic basis for differences in juvenile growth and resistance to the bacterial disease, enteric septicemia of catfish (ESC) in channel catfish, blue catfish, and their hybrids. All possible matings were made among mature channel catfish, blue catfish, and channel x blue hybrids and resulting offspring were measured for weight at 160 days post-hatch, and survival and antibody level (an indicator of immune response) after ESC challenge. Weight at 160 days post-hatch (cross means ranged from 15.7g - 39.8g) and survival after ESC challenge (cross means ranged from 34% - 84%) increased as the percent of the offsprings' genes derived from channel catfish increased. Backcross offspring (matings between a purebred parent and a hybrid parent) and F2 offspring (mating between two hybrid parents) had the poorest survival suggesting that combinations of genes favorable for ESC resistance present in the purebred parents were lost in backcross and F2 matings. Antibody levels after ESC challenge increased as the percentage of channel catfish genes in the progeny increased but antibody levels were not related to survival. The strain of purebred channel catfish tested was as good or better than blue catfish or any of the channel x blue hybrid groups tested for growth and ESC resistance. Hybridization of the strains of channel and blue catfish used in this study would not improve performance for the traits measured.
Technical Abstract: Blue catfish and hybrids among blue and channel catfish typically are more resistant than channel catfish to the bacterium Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish. Information on the genetic basis for phenotypic differences in resistance to E. ictaluri among blue catfish, channel catfish and their hybrids will be useful in evaluating breeding strategies for improving resistance to E. ictaluri. All possible crosses among blue, channel, and blue x channel F1 hybrids were produced by manual spawning of 54 full-sib families (4-7 families/cross). At 160 d post-hatch, 90 fish from each full-sib family were weighed and stocked into polyethylene mesh baskets (30 fish/basket) in 3 replicate raceways, and exposed to virulent E. ictaluri by immersion challenge. Antibody levels (reported as optical density, OD) to E. ictaluri of 15 survivors/family and percent mortality for each family were determined 30 d post-challenge. Cross means ranged from 34.8 - 85.3% for survival, 0.052 - 0.095 OD for antibody level, and 15.7 - 39.8 g for weight at 160 d post-hatch. Channel catfish additive effects were positive for antibody level (0.052 OD) and weight at 160 d (29.4 g) indicating there was a linear increase in antibody level and weight as the proportion of channel catfish genes increased in offspring. Epistatic recombination loss was unfavorable (-31.4%) for survival indicating that loss of favorable epistatic combinations in the parent species resulted in increased mortality in backcross and F2 progeny. Heterosis was negative for weight (-7.5 g). Results indicate that hybridization of the channel and blue catfish strains used in this study would not improve resistance to E. ictaluri or growth of juvenile catfish.