Differences in Growth and Nutrient Efficiency Between and Within Two Channel Catfish Ictalurus punctatus Strains

A 6-wk growth study was conducted comparing fingerling (mean weight = 24.7 g) USDA103 strain channel catfish Zctulunrspunctatus to Norris strain channel catfish in an effort to determine strain dmerences in growth and nutrient efficiency. Variability within strains also was assessed by randomly selecting four families from each strain for comparison. On average, USDA103 fish gained significantly (P < 0.05) more weight (51.2 vs. 31.7 g) and length (4.7 vs. 4.1 cm) compared to Norris strain caffish. Significantly (P < 0.05) greater feed consumption (56.6 vs 41.3 g) and feed efficiency (95.7 vs. 89.9) for USDA103 catfish were also observed. Family differences in weight and length gain and feed intake were significant (P < 0.05) among USDA103 families; whereas, only differences in feed intake and feed efficiency were significant (P < 0.05) among Norris families. Nitrogen retention was higher (P < 0.05) for the Norris strain catfish (35.6%) relative to the USDA103 strain average (31.0%). The results of this study reiterate the superior growth and feed efficiency of the USDA103 strain of channel caffish. Observed differences among USDA103 families suggest that further improvements in weight gain can be made through selective breeding; however, improvements in feed and protein efficiency may be difficult. Improving channel catfish Ictalurus punctatus growth and feed efficiency are two important goals of a selective breeding program. An improved strain of channel catfish, NWAC103, was developed and evaluated at the USDA-ARS Catfish Genetics Research Unit under the experimental name USDA103 and jointly released to commercial producers in cooperation with the Mississippi Agricultural and Forestry Experiment Station, Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi, USA. Results of experimental trials have demonstrated that both the commercial (NWAC103) and experimental (USDA103) lines of catfish have excellent growth compared to other strains of catfish currently being used by commercial producers (Li et d. 1998, 2001; Silverstein et al. 1999, 2000; Jackson et al. 2003; Peterson et al. 2004). Comparison of the USDA103 line of catfish with Norris strain catfish, originating from the Norris fish farm in Arkansas (Dunham and Smitherman 1984) has consistently shown improvements in weight gain and feed consumption for USDA103 catfish, with feed efficiency also shown to be improved 'Corresponding author in some studies (Silverstein et al. 1999; Wolters et al. 2000). To date, no studies have evaluated nitrogen and energy efficiency of the USDA103 strain catfish. Since USDA103 catfish appear to consume more feed than catfish of other common strains, a comparison of nutrient efficiency with a commercially produced strain is warranted. The purposes of this study were to verify genetic differences between Norris and USDA103 catfish strains for growth rate and feed efficiency, determine whether differences exist for nitrogen and energy retention between these two strains, and determine if differences in growth and efficiency indices could be detected among families within the two strains. Methods and Materials