Improvements in Channel Catfish Growth after Two Generations of Selection and Comparison of Performance Traits among Channel Catfish, Blue Catfish, and Hybrid Catfish Fingerlings in an Aquarium Rack System

—A 9-week growth study was conducted to compare the fingerling performance of two genetic groups of channel catfish Ictalurus punctatus (U.S. Department of Agriculture [USDA] 103 and USDA303) with that of blue catfish I. furcatus and their hybrid in an aquarium rack system. Fish of approximately 20 g were randomly selected from multifamily populations and acclimated to the aquarium rack system for 2 weeks prior to the start of the 9-week study. Differences in growth indices, feed and protein efficiency, nitrogen retention, whole-body proximate composition, and plasma cortisol levels were determined at the completion of the study. The USDA303 channel catfish gained significantly more weight and consumed more feed than each of the other genetic groups. Feed and protein efficiency were similar among USDA103, USDA303, and hybrid catfish but were lower for blue catfish. Nitrogen retention was highest for hybrid catfish and lowest for blue catfish. No differences in final body composition were observed between genetic groups when final weight was used as a covariate. Plasma cortisol levels after 9 weeks ranged from 9.7 ng/mL in blue catfish to 24.5 ng/mL in USDA103 channel catfish but were not significantly different among genetic groups. This study demonstrates improved growth of the USDA303 channel catfish after two generations of selection for increased body weight and reports significant differences in performance among channel catfish, blue catfish, and hybrid catfish in an aquarium rack system. The majority of catfish grown and sold in the United States for human consumption are channel catfish Ictalurus punctatus. In the early 1990s, interest in another ictalurid, the blue catfish I. furcatus, as a potential culture species prompted several studies to compare culture characteristics of the blue catfish to those of the channel catfish (Dunham et al. 1990, 1993; Tidwell and Mims 1990). More recently, a slow economy and the threat of foreign fish imports to the profitability of U.S. catfish farming have prompted further interest in the blue catfish as well as renewed efforts in genetic improvement of channel catfish and hybridization between channel catfish and blue catfish. Several studies comparing the performance of channel catfish, blue catfish, and their hybrid in ponds have been published (Dunham et al. 1990, 1993; Tidwell and Mims 1990; Argue et al. 2003; Bosworth et al. 2004; Li et al. 2004). However, little has been published regarding the impact of genotype–environment interactions on performance evaluations. Efficient performance evaluations of large numbers of catfish strains or families require very large pond or tank facilities with good environmental control. Often, the constraints of space and environmental control dictate the use of aquaria for large comparative studies of juvenile performance. The choice of culture system may, however, skew the results of the comparison. In one study, Dunham et al. (1990) found that hybrid catfish grew faster than channel catfish in ponds but grew more slowly than channel catfish in cages. Dunham et al. (1990) suggested that the observed genotype–environment interaction might be caused by behavioral differences between the two genotypes, indicating that hybrids were more active and nervous in confined environments with closer contact to the culturist. Anecdotal evidence suggests that a similar genotype–environment interaction exists for channel catfish, blue catfish, and hybrid catfish reared in