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

Abstract

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 ( Ictalurus punctatus) fingerlings (16.7 g average wt.) were stocked in twenty 400-m 2 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 (BOD 5), chlorophyll a or soluble phosphorus in pond water among treatments; however, TAN, nitrite nitrogen, and BOD 5 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.