Variable feed allowance with constant protein input for channel catfish (Ictalurus punctatus) cultured in ponds

A study was conducted to determine if channel catfish yield in ponds can be maintained with reduced feed allowance, while increasing protein concentration in the diet. Channel catfish (lctalurus punctatus) fingerlings (16.7 g average wt.) were stocked in twenty 400-m2 earthen ponds at a density of 13,750 fish/ha. Diets were prepared to contain three percentages of protein (P) at constant and variable digestible energy (DE) concentrations. One group of diets contained 28%, 32% or 36% protein and a constant level of DE, 3.08 kcal/g of diet. Another group of diets contained the same series of protein percentages and variable levels of DE, 2.70, 3.08 and 3.41 kcal/g, so that DE/P ratio was constant at 9.6 kcal/g. The diet containing 28% protein and 3.08 kcal DE/g diet was the control which was fed at satiation rate. The daily allowance of all the other diets was based upon the amount of protein consumed by the control fish; all treatments received the same daily protein allowance. Therefore, fish fed with the 32% protein diet received 12.5% less feed than the control and those fed with 36% protein diet received 22.2% less than the control. The feeding trial lasted 19 weeks, from June 1 to October 5. When DE level of the diets was constant at 3.08 kcal/g, weight gain of fish was not different (P > 0.05) from the 28% protein treatment (satiation fed) and the 32% protein treatment (87.5% of satiation), but weight gain was lower (P < 0.05) in the 36% protein treatment (77.8% of satiation). When the DE level of the diets changed in proportion to the protein content to provide a constant DE/P ratio, weight gain for the 32% protein treatment (87.5% of satiation) was higher (P < 0.05) than that of the 36% protein treatment (77.8% of satiation), but not different (P > 0.05) from the 28% protein treatment (100% of satiation). Feed efficiency ratio (FER) improved (P < 0.05) as protein level increased from 28% to 32%, with a 12.5% decrease in feed allowance, at constant and variable DE levels; however, FER did not improve (P > 0.05) as protein level increased from 28% to 36%, with a 22.2% reduction in feed allowance. There was no difference (P > 0.05) in total ammonia nitrogen (TAN), nitrite nitrogen, biochemical oxygen demand (BOD5), chlorophyll a or soluble phosphorus in pond water among treatments; however, TAN, nitrite nitrogen, and BOD5 changed (P < 0.05) over time as feed allowance increased. Among the treatments evaluated, commercial fish farmers may find the 32% protein, 3.08 kcal/g DE and 87.5% satiation regimen, the most practical since they can feed to less than satiation, obtain a better FER, and optimize production.