The USDA-ARS initiated a breeding program in 2006 to develop improved channel catfish germplasm for release to U.S. catfish producers. The Delta Select line was selected based on genomic breeding values for growth and carcass yield. In Spring 2020, 2-year-old channel catfish were released to qualified U.S. catfish producers. Twelve catfish producers, representing over 90% of the channel and hybrid catfish fingerling production, received Delta Select channel catfish. Producers report Delta Selects have superior growth compared to their existing catfish lines, with no reports of negative performance. At present, three major producers currently have transitioned to 100% Delta Select broodfish.
Researchers evaluated other production traits in the Delta Selects to determine indirect effects of selection and possible inclusion of additional traits in the selection index. The Delta Control line, a randomly selected population from the same base population as the Delta Selects line, has been maintained for comparison.
Delta Select fingerlings and Delta Control fingerlings were compared for feed conversion efficiency and whole-body proximate composition during an eight-week feeding trial, weight-loss during a two- week feed deprivation trial, and survival following bacterial challenges with virulent Edwardsiella ictaluri (immersion challenge) and Edwardsiella piscicida (injection challenge), bacteria that cause significant mortality in farm-raised catfish.
The feed conversion trial revealed that, compared to the Delta Controls, the Delta Selects had better feed conversion ratio (1.50 vs. 1.82, SE 0.06, p = 0.001), higher percent weight gain (121.3% vs. 95.8%, SE 3.4, p = < 0.0001), and lower percent visceral fat (1.01% vs 1.38%, SE 0.20, p = 0.0008). The feed deprivation trial, the Delta Selects had lower percent weight loss than the Delta Controls (4.71% vs. 5.15%, SE 0.15, p = 0.004). In both bacterial challenges the high dose resulted in greater mortalities than the low dose. There was no difference in cumulative percent mortality between the Delta Selects and Delta Controls following the E. ictaluri challenge (High Dose - Delta Select 54.8 % vs. Delta Control 48.1 %, SE 4.52, p = 0.15; Low Dose - Delta Select 29.8% vs. Delta Control 32.7%, SE 4.52, p = 0.53). Following E. piscicida challenge the Delta Selects had lower mortality than the Delta Controls at both challenge doses (High Dose - Delta Select 63.0% vs. Delta Control 79.8%, SE 5.20, p = 0.003; Low Dose - Delta Select 31.8% vs. Delta Control 48.6%, SE 5.20, p = 0.003).
Feeding trial results suggest selection for growth in the Delta Select line has resulted in improved growth, better feed conversion and reduced fat accumulation. The feed deprivation study suggests selection has impacted physiological processes related to weight-loss in the Delta Selects. Selection does not appear to have negatively impacted susceptibility to E. ictaluri, while potentially improving resistance to E. piscicidia.