Effects of silymarin on growth performance,antioxidant capacity and immune response in turbot (Scophthalmus maximus L.)

A 9‐week feeding trial was conducted using triplicate groups of turbot (6.50 ± 0.01 g) to explore the potential effects of silymarin. Three concentrations of silymarin (100, 200, and 400 mg/kg) were added to the plant protein‐based diet. Fish were randomly distributed into fiberglass tanks (30 fish per tank). The results showed that adding 100 mg/kg silymarin significantly improved the growth performance, with no effects on feed utilization. The antioxidant capacity in the liver was significantly improved in the 100 mg/kg and 200 mg/kg silymarin groups by not only inducing the activities of superoxide dismutase (SOD) and catalase but also increasing the messager RNA (mRNA) expression levels of SOD, glutathione peroxidase, and peroxiredoxin 6. Meanwhile, supplying 100 and 200 mg/kg of silymarin enhanced the heights of villi and enterocytes. Silymarin supplementation reduced the mRNA expression of interleukin‐8 and tumor necrosis factor‐α but induced the expression of transforming growth factor‐β (TGF‐β) in the intestine. These results indicated that silymarin was a potential nutraceutical that could enhance the growth performance and health status of turbot fed in a high plant protein diet. Adding 100 mg/kg silymarin to the plant protein diet achieved optimal performance in turbot.