Dietary tryptophan requirements of juvenile Nile tilapia fed corn-soybean meal-based diets

The objective of this study was to determine the dietary tryptophan (Trp) requirements to optimize growth performance of juvenile Nile tilapia. A hundred and eighty fish (38.2 +/- 0.09 g) were fed to extruded isonitrogenous (28% crude protein) and isoenergetic (14,5 MJ/kg digestible energy) diets, containing graded levels of dietary Trp (1.8, 2.3, 2.7, 3.2, and 3.7 g/kg). Fish were hand fed to triplicate groups of 12 fish, three times a day to apparent satiety for 45 days. The relationship between body weight gain, feed conversion ratio, protein efficiency ratio, and fish uniformity against dietary Trp levels could be expressed as a second-order polynomial regression analysis, where the best Trp levels were estimated to be 2.9, 3.1, 3.1, and 2.9 g/kg, respectively. No effects of dietary Trp on hepatosomatic index, visceral fat, survival, or body composition were observed. Whole body retentions of arginine, phenylalanine, and lysine were highest in fish fed 3.0, 3.1, and 3.1 g/kg Trp, respectively. The dietary Trp requirement of juvenile Nile tilapia was estimated to be 2.9 g/kg for maximum weight gain of fish.