Dietary threonine requirement to optimize protein retention and fillet production of fast-growing Nile tilapia

Abstract

Threonine is the third-limiting essential amino acid in diets based on cereal ingredients. A 4-week trial was conducted to determine the threonine requirement of large Nile tilapia based on fish growth, feed efficiency, body composition, protein and amino acid retention. Six hundred fish (563.3 ± 15.1 g) were distributed into twenty 1.2-m3 cages. Five diets containing 288 g kg−1 of crude protein, 12.7 MJ kg−1 of digestible energy and 8.9, 10.5, 12.2, 13.7 and 15.4 g kg−1 of threonine were elaborated. Fish were hand-fed five times a day to extruded diets. Significantly, differences in growth performance and amino acids retention among the treatments were observed. Fish fed 10.5 g kg−1 of threonine showed higher daily weight gain, gutted weight and fillet weight (P < 0.05) compared to fish fed with other experimental diets. Diets containing 8.9–15.4 g kg−1 of threonine did not affect whole body and muscle proximate composition. Based on second-order regression analysis, the dietary threonine requirement estimated based on final gain, fillet weight and fillet yield was 12, 12.1 and 11.5 g kg−1 diet, respectively. The dietary threonine requirement for maximum fillet yield of Nile tilapia was estimated to be 11.5 g kg−1.