Nitrogen utilization from diets with refined and blended poultry by-products as partial fish meal replacements in diets for low-salinity cultured Florida pompano, Trachinotus carolinus

Three trials were performed to evaluate partial fish meal (FM) replacement with poultry by-products in a practical-type diet for Florida pompano, Trachinotus carolinus reared in low-salinity. Two blended poultry by-product meals (BP67, BP70), two blended chicken concentrates (CC66, CC70) and one standard pet-food grade poultry by-product meal (E150) were evaluated. The diets were formulated to contain 48% crude protein (CP) and 21 MJ/kg. Poultry by-products replaced 67% of the FM protein on an isonitrogenous basis. Trial 1 was a 10 week growth trial with juvenile (3.3 ± 0.10 g) Florida pompano. No differences were detected in growth, efficiency, feed intake, protein productive value, or body composition between the by-product diets and a FM reference diet. Trial 2 examined protein, energy, dry matter, and organic matter digestibility and amino acid availability in 50.0 ± 3.8 g Florida pompano. Apparent CP digestibility (65.6-72.9%) was significantly lower (P < 0.05) in the BP67 diet than the others, except BP70. No other differences were detected. In trial 3, Florida pompano (8.1 ± 0.66 g) were fed a morning meal, and postprandial total ammonia-N (TAN) and urea excretion measured at 8 hourly increments. Ammonia increased 3.1-3.4 fold within 1 h. Rate of TAN excretion (mg TAN/kg∙h) did not significantly decrease until 4-5 h postprandially. No differences in TAN accumulation were observed until 4 h when accumulation was significantly higher (P < 0.05) in CC66, and at 5 h lower in CC70 relative to the FM diet. Rate of urea excretion was constant. A slope ratio analysis indicated there were no differences in urea excretion among the treatments. Stepwise multiple regression suggested that methionine and lysine were the first and second limiting amino acids explaining 99.7% of the variability in weight gain. It is concluded that poultry by-products are suitable partial replacements for FM in Florida pompano diets.