GROWTH, FEED-EFFICIENCY AND BODY-COMPOSITION OF 2ND-YEAR AND 3RD-YEAR CHANNEL CATFISH FED VARIOUS CONCENTRATIONS OF DIETARY-PROTEIN TO SATIETY IN PRODUCTION PONDS

Two pond-feeding experiments were conducted with channel catfish (Ictalurus punctatus), one for second-year fish and the other for third-year fish, in which the fish in 400-m2 earthen ponds were fed five practical-type diets that contained 24, 28, 32, 36 or 40% crude protein. The diets were similar to those used commercially, with major ingredients being soybean meal, grain products, fish meal, and vitamin and mineral supplements. Protein concentration of the diets was increased by substituting a fixed ratio of soybean meal to fish meat (5:1) for corn. Energy concentration of the diets was not regulated. All diets were adequate in essential amino acids on a percentage-of-protein basis. In experiment 1, the fish were fed from an average size of 20 g to 488 g (151 days) at a stocking density of 13 590 fish per ha and in experiment 2 the fish were fed from an average size of 594 g to 1632 g (141 days) at a stocking density of 4942 fish per ha. Each diet was fed in four replicate ponds, once daily to satiation through the growing seasons. Increasing dietary protein concentration had no significant effect on weight gain of second-year fish and a negative linear effect on weight gain of third-year fish. Increasing dietary protein had no significant effect on feed consumption of second-year fish and a negative linear effect on food consumption of third-year fish. Weight gain was positively correlated with feed consumption in both groups and feed conversion was not significantly affected by the dietary protein concentration. Efficiency of protein utilization decreased linearly as dietary protein increased. Dressing percentage increased as dietary protein increased from 24 to 36% and decreased as dietary protein increased from 36 to 40% in second-year fish, but dressing percentage was not affected by dietary protein concentration in third-year fish. In both groups muscle fat decreased linearly, while protein and moisture increased, as dietary protein increased. Second-year fish had lower feed conversion, lower dressing percentage and less muscle fat than third-year fish. The results indicate that second- and third-year channel catfish in highly intensive cultures will gain maximally on feeds containing no more than approximately 24% crude protein with satiate feeding, although muscle fat content will be higher and dressing percentage (of second-year fish only) will be lower with the low-protein diet. Second-year fish have advantages over third-year fish in higher feed efficiency and less muscle fat, but have the disadvantage of lower dressing yield.