Effects of dietary selenium supplementation in high-plant-protein diets on the growth performance, body composition, PPAR gene expression and intestinal inflammatory response of juvenile turbot (Scophthalmus maximus)

Plant proteins have been increasingly used as sustainable substitutes for fish meal in aquafeeds, however, their high inclusion level compromises fish performance. Selenium (Se) is an essential micronutrient required for normal development and antioxidant protection, but its effects on the growth, physiological metabolism and immunity of marine fish in response to high plant protein diet need further research. To investigate the effects of sodium selenite on the growth performance, body composition, ppars gene expression and intestinal inflammatory response of juvenile turbot fed high plant protein diet. A total of 525 turbot with an average weight of (30.79±0.22) g were randomly divided into 7 groups(with 3 replicates in each group): DP, DN, D1, D2, D3, D4 and D5, respectively. After 52 days feeding trial, the results showed that sodium selenite supplementation alleviated the growth inhibition caused by the high plant protein diet, mainly by improving weight gain rate (WGR), specific growth rate(SGR), protein efficiency ratio(PER) and condition factor(CF). Feed coefficient showed the opposite trend and was significantly higher in DN group than in other groups. In the fish body composition, the crude lipid content of whole fish and dorsal muscle in DN group was significantly decreased, and the crude lipid content of liver was significantly increased. Appropriate sodium selenite can relieve liver lipid accumulation caused by low fish meal. In addition, sodium selenite mitigated the decreased serum activities(total cholesterol, lysozyme, alkaline phosphatase and total superoxidedismutase) of the high plant protein diet. Appropriate sodium selenite addition can inhibit the decrease of pparα1, pparα2 and pparβ mRNA levels and increase of pparγ mRNA levels induced by the high plant protein diet. Sodium selenite can also increased the content of TGF-β1 and decreased the contents of TNF-α and IL-6 in intestinal. In conclusion, sodium selenite mitigated the negative effects of the high plant protein diet on the growth performance, hepatic lipid deposition, immunity and intestinal health, and the recommended supplemental level of sodium selenite in the high plant protein diet was 0.6~2.4 mg/kg. This study lays a theoretical foundation for further exploring the application of sodium selenite in aquatic formulate feed.