Genetic studies on reproduction, bacterial disease resistance and tolerance of adverse water quality in channel catfish, Ictalurus punctatus

Five experiments were conducted to determine reproductive performance, bacterial disease resistance, parasite resistance and tolerance to adverse water quality among commercial and research populations of channel catfish, Ictalurus punctatus. In the first experiment, commercial populations of channel catfish were open pond spawned in pure strain and crossbreeding combinations and evaluated for reproductive success, spawning rate, fertility, egg weight, egg mass, fecundity, hatching rate and progeny survival on-farm. In the second experiment, progeny derived from commercial populations in the first experiment were compared to on-station research populations of channel catfish, to determine the effect of crossbreeding on resistance to two bacterial diseases: enteric septicemia of catfish (ESC) and columnaris. Tolerance to adverse water quality, low (<1.0 mg/L) dissolved oxygen and lethal (12 mg/L) levels of nitrite were also evaluated. The third and fourth experiments, respectively, assessed the efficiency of direct selection and indirect selection for improving bacterial disease resistance and tolerance to adverse water quality. In the fifth experiment, the effect of selection and crossbreeding for reducing external parasite load was determined.; Differences (P < 0.05) were observed in reproductive success among strain and crossbred matings of channel catfish derived from commercial populations. Genotype X environment interactions (P < 0.05) in fry survival were observed under hatchery, raceway and pond environments. Rate of albinism was different (P < 0.05) among strain and crossbreeds derived from the commercial genotypes.; Differences were observed among both commercial and research populations of channel catfish for ESC and columnaris resistance. Genotypes derived from the two populations also exhibited differences (P < 0.05) in oxygen and nitrite tolerance. Crossbreeding improved (P < 0.05) ESC resistance in the MSXKS genotype derived from research populations. Selection for increased body weight in the KS line improved columnaris resistance and tolerance to high nitrite. Oxygen tolerance and parasite resistance decreased when KS and MS lines were selected for increased body weight. Direct selection for ESC and columnaris resistance in the KDS line did not improve both resistance to these bacterial disease or tolerance of adverse water quality. The MSXKS crossbreed had the best overall performance for increasing tolerance of bacterial and parasitic pathogens and adverse water quality conditions.