Influence of dietary Se supplementation on aquaponic system: Focusing on the growth performance, ornamental features and health status of Koi carp ( Cyprinus carpio var . Koi ), production of Lettuce ( Lactuca sativa ) and water quality

In order to explore the influence of dietary selenium supplementation on growth, ornamental features and health status of Koi carp, yield of Lettuce, and water quality under aquaponic condition. Koi (125.26 ± 12.55 g) were fed diets containing 0, 0.6, 1.2 and 2.4 mg nano‐Se kg ‐1 for 8 weeks respectively. The weight gain rate in 0.6 and 1.2 mg/kg nano‐Se group was significantly higher than control group ( p  < .05), feed conversion ratio in 1.2 mg/kg nano‐Se group was significantly lower than control ( p  < .05). Carotenoids content in tissues was significantly increased in 1.2 mg/kg nano‐Se group compared with control ( p  < .05), and skin redness of 2.4 mg/kg nano‐Se group was significantly higher than control ( p  < .05). Malondialdehyde level in 1.2 mg/kg nano‐Se group was significantly lower than the control and 2.4 mg/kg nano‐Se group ( p  < .05). Total serum protein content increased significantly in 1.2 and 2.4 mg/kg nano‐Se groups compared with control ( p  < .05), and serum globulin increased significantly in 2.4 mg/kg nano‐Se group compared with control ( p  < .05). The yield of lettuce was not influenced by the dietary Se ( p  > .05). The ammonia and nitrite in 1.2 mg/kg nano‐Se group were significantly lower than that in control ( p  < .05). The quadratic regression model of growth and dietary Se levels showed that optimal amount of Se was 1.55–1.57 mg/kg. Overall, dietary nano‐Se supplementation could improve the growth, pigment deposition and health status of Koi and effectively improve the aquaculture environment under aquaponic condition.