Effects of three tested medicinal plant extracts on growth, immune function and microflora in juvenile largemouth bass (Micropterus salmoides)

This study aimed to explore the effects of three medicinal plant (Perilla frutescens, Illicium verum, and Artemisia annua) extracts on growth, immune function and microflora of largemouth bass (Micropterus salmoides). Four isonitrogenous and isolipidic diets were formulated: basic feed (control, CON), 0.075% extracts of Perilla frutescens (PFE), Illicium verum (IVE), or Artemisia annua (AAE) feed. Apparently healthy fish (initial body weight of 8.20 ± 0.03 g; total number of 300) were randomly assigned into four groups in triplicate 25 fish tanks, and fish were fed with each of the four experiment feeds for 80 days. Compared with the CON group, groups IVE and AAE fish significantly improved growth performance (final weight, weight gain rate, and specific growth rates; P < 0.05) and decreased hepatic lipid content and hepatopancreas somatic index. Groups IVE and AAE significantly enhanced the hepatic antioxidant capacity (Catalase, Glutathione peroxidase dismutase, and Superoxide dismutase), and up-regulated the mRNA levels of hepatic tight junction protein (Occluding-1 and Claudin-1; P < 0.05) and anti-inflammatory cytokines (interleukin-10 and transforming growth factor-β; P < 0.05). In addition, groups IVE and AAE decreased the transaminase activity and the contents of D-lactic acid in serum (P < 0.05). Groups PFE and AAE significantly improved albumin and globulin contents in serum immunity (P < 0.05). In addition, IVE and AAE groups significantly increased the α-diversity of intestinal flora, reduced the abundance of underlying harmful bacteria (Plesiomonas and Aeromonas), and increased the abundance of probiotics bacteria (Lactobacillus and Weissella; P < 0.05). These results demonstrate that supplementation of feed with IVE and AAE can improve the immune function and change the abundance of intestinal flora, ultimately increasing growth of largemouth bass. Overall, PFE group did not perform well compare with the IVE and AAE groups.