Dietary lysine requirement to enhance muscle development and fillet yield of finishing Nile tilapia

The dietary lysine requirement has not been established for finishing Nile tilapia despite being considered the first limiting essential amino acid in many cereal grain ingredients. A feeding trial was designed to determine the dietary lysine requirement using 600 fish (274.9 +/- 3.3 g) distributed into 15, 1.2 m(3) net cages in a completely randomized design with five treatments and three replicates. Five extruded isoproteic (251.2 g of crude protein kg(-1)) and isoenergetic diets (13.1 MJ of digestible energy kg(-1)) containing 11.1, 12.5, 13.9, 15.1 and 16.4 g lysine kg(-1) were prepared. Fish were hand fed four times a day until apparent satiety. Fish fed 15.1 g lysine kg(-1) exhibited improved final body weight and daily weight gain compared to fish fed 11.1 g lysine kg(-1). Fillet weight and fillet yield of finishing Nile tilapia were significantly affected by dietary lysine levels and optimized at 15.1 g lysine kg(-1) compared to fish fed the other treatments. Whole-body and fillet compositions of fish were unresponsive to dietary lysine levels. Whole-body lysine, tryptophan, alanine, aspartic acid and tyrosine retention was significantly affected by dietary lysine levels. Although the recruitment of new fibers by hyperplasia continues in adult Nile tilapia, the predominance of muscle growth was by hypertrophy as observed in fish from all treatments. Based on second-order regression analysis, the dietary lysine requirement for maximum fillet yield of finishing Nile tilapia was estimated at 14.6 g kg(-1), corresponding to 5.8% of dietary protein. Statement of relevance: First mention of lysine requirements of large Nile tilapia (C) 2016 Elsevier B.V. All rights reserved.