Effects of dietary protein levels on growth performance, digestibility, anti‐oxidative responses and expressions of growth‐related genes in triploid rainbow trout <i>Oncorhynchus mykiss</i> farmed in seawater
Guangxia Liu, Liu Wang, Haixia Yu, Mingzhu Pan, Mengxi Yang, Wenbing Zhang, Kangsen Mai
Abstract
An 8-week feeding trial was performed to investigate the effects of dietary protein levels on growth, feed utilization, digestive and absorptive capability, anti-oxidative ability and expressions of growth-related genes of triploid rainbow trout Oncorhynchus mykiss farmed in seawater. Fish (109.03 ± 0.04 g) were randomly fed one of the seven isolipidic and isoenergetic diets containing graded levels of protein (300, 350, 400, 450, 500, 550 and 600 g/kg, respectively). Dietary protein levels linearly and quadratically increased the final body weight and weight gain rate (WGR). Feed conversion ratio had significant negative linear and quadratic responses to the dietary protein levels. The apparent digestibility coefficients of dry matter and crude protein were linearly and/or quadratically increased by dietary protein levels. Pepsin, trypsin, chymotrypsin, γ-glutamyl transpeptidase, alkaline phosphatase, creatine kinase and Na+, K+-ATPase activities and expression of peptide transporter 1 were linearly and/or quadratically improved by dietary protein levels. Activities of glutathione peroxidase, catalase, superoxide dismutase and the total anti-oxidative capacity were affected positive linearly and/or quadratically by dietary protein levels. Expressions of growth hormone receptor 1 (GHR1), insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II) as well as target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6 K1) were linearly and/or quadratically increased by dietary protein levels, while insulin-like growth factor binding protein 1b (IGFBP1b) expression had a negative quadratic response to dietary protein levels. In conclusion, quadratic regression analysis of WGR displayed that dietary protein requirement of triploid rainbow trout (109.03 ± 0.04 g) reared in seawater was 467.6 g/kg. Dietary protein could influence the growth of seawater-farmed triploid rainbow trout through GH-IGFs axis and TOR/S6 K1 pathway.