Influence of differential protein levels of feed on growth, copper‐induced immune response and oxidative stress of Rhynchocypris lagowski in a biofloc‐based system

Abstract

This study compared the influences of differential protein levels of feed on growth, copper-induced digestive enzyme activity, immune response, oxidative stress and Nrf2 signalling molecules genes expression of Rhynchocypris lagowski in a biofloc-based system and traditional autotrophic system. Four hundred and fifty R. lagowski were fed four experimental dietary containing graded levels of protein from 25% to 37% (referred as biofloc technology [BFT]25, BFT29, BFT33 and BFT37, respectively) in a biofloc-based system, and 37% crude protein level (control group) were cultured in an autotrophic system in 8 weeks. At the end of the trial, there was an improvement of 50.35%–61.64% in terms of growth performance (weight gain rate); 0.25–0.53 (U/mg prot) amylase; 6.9–8.02 (U/ml) lysozyme (LZM); and 7.98–8.12 (U/ml) total superoxide dismutase (T-SOD) in R. lagowski cultured in BFT37 groups as compared to control. Obviously, the growth performance, digestive enzymes activity, immune response, antioxidant statue and antioxidant-related genes expression of R. lagowski fed with the same protein level in BFT system were significantly higher than those in the control group (p < .05). Furthermore, the level of T-SOD in liver and kidney and interferon-γ in liver of BFT33 group were also significantly higher than that of control group (p < .05). Moreover, there was no notable difference of LZM, alkaline phosphatase, complement C3, C4, heat shock proteins 70, heat shock proteins 90, insulin-like growth factor I, glutathione peroxidase, catalase, total antioxidant capacity, malondialdehyde, Ascorbic acid in gill, liver, kidney, gut and serum among the BFT29 groups and those in the control (p > .05). Besides, bioflocs assists in regulating the expression of Nrf2 signalling molecules including Nrf2, Keap1, Maf, HO-1, CAT, CuZn-SOD, GPX and GCLC. We summarized that despite the low protein content in feed, BFT system has the potential to promote growth performance, alleviate copper-induced immunosuppression and oxidative stress of juvenile R. lagowski.