Effect of mixture of Artemisia argyi and Houttuynia cordata Thunb extracts on growth performance, antioxidant activity, serum and hepatic lipid levels, and gut bacteria in grass carp (Ctenopharyngodon idella)

Artemisia argyi and Houttuynia cordata Thunb are common herbs in most regions of China. In order to test their composite effect as additives on fish, the effects of their extracts mixture on growth performance, antioxidant activity, serum and hepatic lipid levels, and gut bacteria in juvenile grass carp were evaluated. 180 fish were divided into 9 tanks with 3 replicate tanks per treatment, and fed with a control diet (A0) or one of two treatment diets containing 500 (A1) or 1000 mg/kg (A2) mixture of extracts, with equal mass of A. argyi and H. cordata, for 8 weeks. Water flow rate was 8.0 L/min, and water quality parameters were in normal range. At the end of feeding trial, fish weight gain, feed conversion ratio, and survival rate showed no difference among all groups. Significantly higher catalase (CAT) activity and lower malondialdehyde (MDA) content were observed in A1 and A2 groups. Serum triglyceride content was much lower in the A1 group and total cholesterol was lower in experimental groups compared with the control group. Transmission electron microscopy showed that the hepatic lipid droplets were smaller in the experimental groups. High-throughput sequencing identified 10 predominant phyla from gut samples, and Fusobacteria, Bacteroidetes, and Proteobacteria were the most dominant groups. Compared with the control group, in A1 group operational taxonomic unit (OTU) number, species richness (Chao1, and ACE), and α diversity (Shannon index) were higher, and gut bacteria composition was altered in A1 and A2 groups at phylum and genus levels. These results indicated that the extracts mixture of A. argyi and H. cordata can increase antioxidant activity, lower serum and hepatic lipid levels, and improve gut bacteria composition, which can be used as a green additive for grass carp.