Effect of Dietary Protein Concentration on Nitrogenous Waste in Intensively Fed Catfish Ponds

Abstract

AbstractChannel catfish were fed five diets containing 24, 28, 32, 36 or 40% protein in intensively stocked earthen ponds over a 141 d growing season. Mean standing crop at harvest was 7,559 kg/ha, and maximum daily feed allowance was 105 kg/ha. Dietary protein concentration had a negative linear effect on weight gain. Total ammonia‐nitrogen (TAN) in pond water increased linearly as dietary protein concentration increased and was positively correlated with total protein fed. However, unionized ammonia‐nitrogen (NH3‐N) was not influenced by dietary protein concentration. Dietary protein had a positive linear effect on nitrite‐nitrogen (NO1‐‐ ‐N) concentration, which was positively correlated with total protein fed and TAN. There was no significant correlation between NO2‐‐‐N and fish weight gain, although there was a significant positive correlation between NO2‐‐ ‐N/Cl‐molar ratio in pond water and concentration of methemoglobin in the fish. Results from this study indicate that when the feeding rate is as high as 100 kg/ha/d, or 3,000 kg protein/ha/season, dietary protein concentrations of 36% and above can result in harmful concentrations of NO2‐‐‐N when Cl concentration in the ponds is 2–3 mg/L. Although the NO2‐‐‐N/Cl‐ ratio in the ponds increased to harmful levels with protein concentration of the diets, this might not be the major cause of the reduction in fish growth rate as dietary protein increased because the greatest difference in weight gain occurred at the lower protein concentrations and the greatest difference in NO2‐‐‐N occurred at the higher dietary protein concentrations.