Dietary histidine requirement of Nile tilapia juveniles based on growth performance, expression of muscle-growth-related genes and haematological responses

A 100-day feeding trial was carried out to determine the dietary histidine requirement of Nile tilapia juveniles based on growth performance, muscle development, expression of muscle-growth-related genes, biochemical and hematological responses. Nile tilapia juveniles (4.84 +/- 0.04 g) were fed six extruded practical isonitrogenous (265.7 g of crude protein kg(-1)) and isoenergetic (17.3 MJ of gross energy kg(-1)) diets containing graded levels of histidine (4.2, 5.4, 7.1, 8.9, 9.8 and 11.5 g kg(-1) dry diet). The feeding trial was conducted in a flow-through system (1.5 L min(-1)) at 28 degrees C water temperature, and triplicate groups of fish were hand-fed each diet four times a day until apparent satiation. Final weight, weight gain, feed conversion ratio, protein efficiency ratio and net protein utilization were optimized in fish fed 8.9 g of histidine kg(-1). Whole-body protein content was enhanced in fish fed 7.1 and 9.8 g of histidine kg(-1) compared to fish fed 11.5 g of histidine kg(-1). Active hypertrophic growth process was observed in fish fed 8.9 g of histidine kg(-1), as confirmed by lower frequency of occurrence of muscle fibers <20 mu m diameter and higher frequency of occurrence of muscle fibers >50 mu m diameter, compared to fish fed 5.4 g of histidine kg(-1). Fish fed 9.8 g of histidine kg(-1) showed the highest expression level of MyoD. However, myogenin expression was higher in fish fed 9.8 and 11.5 g of histidine kg(-1) compared to fish fed 4.2 to 7.1 g of histidine kg(-1). Myostatin expression was similar among fish from all treatments. Biochemical and haematological responses were not affected in fish fed graded levels of histidine. Based on second-order regression analysis, the dietary histidine requirement for maximum WG of Nile tilapia juveniles was estimated to be 8.2 g kg(-1), corresponding to 3.1% of crude protein. Statement of Relevance: Histidine is a limiting amino acid in Nile tilapia diets. (C) 2016 Elsevier B.V. All rights reserved.