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

Abstract

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±0.04g) were fed six extruded practical isonitrogenous (265.7g of crude protein kg−1) and isoenergetic (17.3MJ of gross energy kg−1) diets containing graded levels of histidine (4.2, 5.4, 7.1, 8.9, 9.8 and 11.5gkg−1 dry diet). The feeding trial was conducted in a flow-through system (1.5Lmin−1) at 28°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 8.9g of histidine kg−1. Whole-body protein content was enhanced in fish fed 7.1 and 9.8g of histidine kg−1 compared to fish fed 11.5g of histidine kg−1. Active hypertrophic growth process was observed in fish fed 8.9g of histidine kg−1, as confirmed by lower frequency of occurrence of muscle fibers <20µm diameter and higher frequency of occurrence of muscle fibers >50 µm diameter, compared to fish fed 5.4g of histidine kg−1. Fish fed 9.8g of histidine kg−1 showed the highest expression level of MyoD. However, myogenin expression was higher in fish fed 9.8 and 11.5g of histidine kg−1 compared to fish fed 4.2 to 7.1g 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 8.2gkg−1, corresponding to 3.1% of crude protein. Statement of RelevanceHistidine is a limiting amino acid in Nile tilapia diets.