Effects of dietary chitosan oligosaccharide complex with rare earth on growth performance and innate immune response of turbot, S cophthalmus maximus L .

An 8‐week‐feeding trial was conducted to investigate the effect of dietary chitosan oligosaccharide complex with rare earth ( COS ‐ REE ) on growth performance and innate immune response of turbot, S cophthalmus maximus L . (Initial average weight was (12.1 ± 0.1) g) as well as disease resistance against E dwardsiella tarda . Six practical diets (approximately 53.01% protein and 12.57% lipid) were formulated to contain graded levels (0, 75, 150, 300, 600 and 1200 mg kg −1 ) of COS ‐ REE . Results of the present study showed that, compared to the control group (0 mg kg −1 ), the specific growth rate ( SGR ) was significantly higher in fish fed the diet with 300 mg kg −1 COS ‐ REE ( P  <   0.05), while the feed conversion ratio ( FCR ) significantly decreased ( P  <   0.05). The phagocytic index ( PI ) and the activity of super oxide dismutase ( SOD ) of serum in fish fed the diet with 300 mg kg −1 COS ‐ REE was significantly higher than fish fed the control diet ( P  <   0.05), but no significant differences were observed in malondialdehyde ( MDA ) and hepatic metallothionein ( MT ) concentrations. After 8 weeks, fish were challenged by intraperitoneal injection with E . tarda , and COS ‐ REE ‐treated fish demonstrated increased protection capability. These results suggested that COS ‐ REE could enhance growth, innate immunity and disease resistance in turbot, and the optimum dose was approximately 300 mg kg −1 .