Effects of dietary protein levels on growth performance, digestibility, anti‐oxidative responses and expressions of growth‐related genes in triploid rainbow trout Oncorhynchus mykiss farmed in seawater

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.

Dietary Effects of Lipid and Protein Levels on Growth, Feed Utilization, Lipid Metabolism, and Antioxidant Capacity of Triploid Rainbow Trout (Oncorhynchus mykiss)

“…In this study, there was no difference in WG, FCR, PR, PER between the P44 and P49 groups at the same dietary lipid level (P >0:05), suggesting that 44% crude protein level might have met the requirement of rainbow trout. The present findings were similar to the reported protein requirement of 45.8% [19] and 46.76% [28] (both at 20% crude lipid level) for triploid rainbow trout.…”

“…However, few research has been conducted on the nutritional requirements of triploid rainbow trout. The appropriate dietary protein level was 45.8% [14] and 46.76% [28] for 232.8 and 109.03 g triploid rainbow trout in dietary lipid level of 20%, respectively. In a diet with 46% crude protein, for 233 g triploid rainbow trout, the appropriate dietary lipid level would be 23.3% [19] or ≥22.8% [11], respectively.…”

Effects of Dietary Protein and Lipid Levels on Growth, Metabolism, Antioxidative Capacity, and Fillet Quality of Adult Triploid Rainbow Trout Farmed in Net Cage

“…They can minimize energy consumption for gonad development, avoid reproductive problems (i.e., high mortality and the decline in fillet quality), and shorten the culturing period. Triploid rainbow trout are particularly attractive commercial fish due to their large size (≥2.5 kg) and great economic worth [ 2 ].…”