Protein-to-energy ratios in production diets and growth, feed conversion and body composition of channel catfish, Ictalurus punctatus

Abstract

Channel catfish fingerlings were stocked in 400-m 2 earthen ponds at densities of 75 fish per 100 m 2 and fed to satiety with diets containing 26, 31, 35 and 39% protein, or 91, 107, 120 and 127 mg of protein/kcal of digestible energy (DE), for 123 days. The diets were similar to those fed commercially, composed of soybean meal, corn, a small amount of fish meal and vitamin and mineral supplements. The protein-to-energy ratio ( P E ) was increased by substituting a fixed ratio of soybean meal and fish meal (5:1) for corn. All diets were adequate in essential amino acids on a percentage-of-protein basis. There was a general increase in live weight, dressed weight, and protein gains as dietary protein increased. Weight gain increased markedly, from 288 g/fish to 407 g/fish, when dietary protein increased from 26 to 31% ( P < 0.01), but less, from 429 g/fish to 476 g/fish, when protein increased from 35 to 39% ( P < 0.10). Feed conversion improved from 1.39 g feed/g gain in the 26% protein diet to the lowest value, 1.15 g feed/g gain, in the 35% protein diet. Dressing percentage was lowest for fish fed the 26% protein diet, 58.6, but not different among fish fed the three higher protein feeds, which averaged 61.3. Body fat was highest in fish fed the 26% protein diet, 9.3%, and lowest in those fed the 35% protein diet, 7.5%. The optimum P E ratio in a soybean meal-fish meal-corn catfish diet for rapid growth, efficient feed conversion and high ratio of protein-to-fat gain appears to be approximately 120 g of protein/kcal of DE. These results show trends in fish responses to variable dietary P E ratios which indicate that the amount of protein in commercial catfish feeds should be chosen on the basis of feed ingredient costs and fish prices.