The effects of dietary Eucommia ulmoides Oliver on growth, feed utilization, antioxidant activity and immune responses of turbot (Scophthalmus maximus L.)

The present study was conducted to evaluate the effects of dietary Eucommia ulmoides (EU) on growth, feed utilization, antioxidant activity and immune responses of turbot fed a basal diet (CON) or EU-supplemented diets with 5.0 g/kg (EU1), 10.0 g/kg (EU2) and 20.0 g/kg (EU3) EU leaf powder. After 70-day trial, EU supplementation did not affect nutrient utilization, but reduced feed intake (FI) and specific growth rate (SGR) of fish at doses above 5.0 g/kg. Superoxide dismutase (SOD), catalase (CAT) and total antioxidant capacity (T-AOC) activities in the EU-supplemented groups were significantly higher than those in the control group at a dose of 20.0 g/kg. Significantly reduced malondialdehyde (MDA) contents were observed in EU-supplemented groups at doses over 5.0 g/kg. Furthermore, fish fed 20.0 g/kg EU showed the highest lysozyme (LZM) activity among groups. The EU-supplemented diets with doses above 5.0 g/kg significantly enhanced the mRNA expressions of cytokines. The expression level of major histocompatibility complex II alpha (MHC II alpha) was significantly upregulated compared to that of the control fish when the supplemental level was at 20.0 g/kg. Taken together, the present study indicated that the EU could remarkably enhance the antioxidant activity, non-specific immunity and maintain an active immune response in turbot.