|dc.description.abstract||The channel catfish, Ictalurus punctatus × blue catfish, I. furcatus hybrid shows increased performance over the channel catfish for many traits, including tolerance of low dissolved oxygen. Performance of hybrid offspring might be further improved by selecting for desired traits in the parents based on combining ability. In addition, analysis of combining ability may aid in identifying parental strains that produce better performing hybrid offspring. Using a full factorial 6 × 6 experimental design, fry from 36 different families of hybrid catfish were produced to measure general (GCA) and specific (SCA) combining abilities for resistance to low levels of dissolved oxygen (DO).
The dam GCA was observed and accounted for 9.5% of the variance for survival when hybrid progeny were exposed to 0.6 ppm, whereas the sire GCA and SCA were zero. Thus, selecting for channel catfish females with increased tolerance of low dissolved oxygen should improve, and would be predicted to be the best mechanism to enhance, the genetic ability of the hybrid progeny to tolerate low dissolved oxygen.
Interpretation of the time to death was more complicated. If the surviving fish are included in the analysis, dam GCA accounts for 25% of the variation, sire GCA only 3% and SCA, 0%. Again, the best genetic enhancement approach will be to select for channel catfish lines resistant to low oxygen. However, if the survivors are not considered in the analysis, the genetics of hybrid tolerance of low oxygen changes. Dam GCA reduces to 8%, sire GCA reduces to 0% and SCA becomes the most important genetic factor, increasing to 17% of the total variance. How the trait is defined and analyzed has a large impact on both interpretation and recommended breeding program practices. Results were similar, but not exactly like those obtained in another study when hybrid fingerlings averaging 58g were evaluated to determine combining ability for low DO tolerance.
The results of this study could influence genetic selection programs on a commercial scale for the selection of hybrid fry and fingerlings that have improved tolerance to low dissolved oxygen level. Using hybrids with improved tolerance to low dissolved oxygen allows for increased stocking densities and more fish available at harvest.||en_US