Flavonoid‐enriched diets improved the growth and flesh quality of grass carp ( Ctenopharyngodon idellus ) based on metabolomics

This study investigated the effects of four flavonoids on growth and flesh quality of grass carp (Ctenopharyngodon idellus). Five diets were designed with the supplementation of quercetin (QC), rutin (RT), baicalein (BC) and catechin (CC) in basal diet (control) and were fed to grass carp (59.7 ± 0.2 g) for 60 days. The fish fed QC and RT diets, rather than BC and CC diets, showed higher weight gain (+4.0%, +3.9%) and lower feed conversion ratio (−0.07, −0.06) than the control fish. The contents of total collagen, heat-soluble collagen, total free amino acids and flavour amino acids in flesh were significantly increased by the supplementation of QC and RT in diets. The SOD activity and the contents of C22:5, C22:6 and n-3 PUFA were significantly increased, and the malondialdehyde and protein carbonyl contents were significantly decreased in the QC, RT and CC groups. In the metabolomics profiling of muscle, 102 and 68 named differential metabolites were identified in the QC and RT groups, and these metabolites were found to be involved in the pathways of “lipid metabolism” and “amino acid metabolism.” In addition, the mRNA expressions of IGF-1, PI3K, AKT and FAS in flesh were significantly up-regulated in QC and RT groups. In summary, dietary QC and RT promoted the growth and flesh quality of grass carp which might be associated with IGF-1/TOR, Nrf2, TGF-β/Smad4 and PPAR signalling pathway.