Effects of dietary isoleucine on growth performance, enzymatic activities, antioxidant properties and expression of TOR related genes in rainbow trout, Oncorhynchus mykiss fingerlings

摘要

Abstract An 8‐week feeding trial was conducted to determine dietary isoleucine (Ile) requirement of rainbow trout, Oncorhynchus mykiss fingerlings. Six isonitrogenous (450 g kg−1) and isocaloric (20.90 kJ g−1, gross energy) diets were designed with varied Ile levels (6.0–18.5 g kg−1, dry diet). Twenty fish (1.66 ± 0.02 g/fish; 5.25 ± 0.34 cm/fish) were distributed in triplicate groups in 75‐L troughs attached to flow‐through system (2–2.5 L minute−1) and were fed twice daily (09:00 and 17:00 hours) at 5 BW day−1. Maximum live weight gain (LWG ), specific growth rate (SGR), protein efficiency ratio (PER) and the best‐feed conversion ratio (FCR) were observed at 13.5 g kg−1 Ile fed diet. Quadratic regression analysis of growth data predicts optimum Ile requirement to be at 13.73 (LWG ), 13.41 (FCR), 13.44 (PER) and 13.35 (BPD) g kg−1 respectively. Highest (p  0.05) changes among the groups, while as alanine transaminase (ALT), aspartate transaminase (AST) and uric acid levels showed significant (p ˂ 0.05) variations. Highest total protein content and lowest alkaline phosphatase (ALP) were observed at 13.5 g kg−1 Ile fed diet, while albumin and globulin content did not produce any significant (p > 0.05) difference among the groups. Significant (p ˂ 0.05) differences were also observed in intestinal enzymatic activities and antioxidant status. Highest (p < 0.05) TOR and 4E‐BP mRNA gene expression level were also found at 13.5 g kg−1 Ile fed diet. On the basis of above data, it is recommended that 13.48 g kg−1 Ile, corresponding to 29.95 g kg−1 of dietary protein, would be useful for optimum growth and best nutrient conversion of this species.