Effects of Sophora flavescens dietary supplementation on the growth performance, haematological indices, and intestinal bacterial community of Oreochromis niloticus

Sophora flavescens is considered to be of various medicinal and economic importance. Previous studies have shown that it has antibacterial, antioxidant, and immune-enhancing functions. To explore the full potential of S. flavescens in fish feed development, we investigated the effects of different levels of S. flavescens added to the diet on the growth performance, haematological indices, and the intestinal bacterial community of Nile tilapia (Oreochromis niloticus). The feeding trial lasted for 56 days, and the initial weight of the fish was 40.00 +/- 5.00 g. Nile tilapia were randomly divided into six groups: a control group (CN) and five S. flavescens supplementation groups (0.02%, 0.04%, 0.08%, 0.16%, and 0.3% [w/w] of S. flavescens in diet). The growth performance of fish increased first and then decreased with the increase of S. flavescens supplemental level. Compared with other experimental groups, the growth performance of fish supplemented with 0.08% S. flavescens was significantly improved (p < 0.05). Haematological indices exhibited that erythrocyte (RBC), along with leucocyte (WBC) indices, exhibited a secondary trend of increasing and then decreasing with the increase of S. flavescens, reaching the highest level at 0.08% (p < 0.05). However, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), and mean corpuscular haemoglobin concentration (MCHC) exhibited a secondary trend of first decreasing and then increasing with the increase of S. flavescens and reached the lowest value at 0.08% (p < 0.05). Compared with the CN, alkaline phosphatase (AKP) significantly decreased and changed when the additional amount of S. flavescens was 0.04% in each treatment group (p < 0.05). In another way, the gut microbial profiles revealed that Bacteroides dominated the gut communities, and compared with the control group, two uncultured bacteria were suppressed. In addition, when the supplemental level of S. flavescens was more significant than 0.04%, the proliferation of Arcobacter cryaerophilus, Solibacillus silvestris, and Escherichia sp. in the gut of Nile tilapia was promoted. The results revealed that S. flavescens, as an additive to the Nile tilapia diet with levels ranging from 0.04% to 0.08%, can enhance the growth performance and immunity and promote the proliferation of intestinal beneficial bacteria of Nile tilapia.