The aim of this study was to investigate the effects of an effective microorganism (EM)‐based microbial inoculum on the growth and expression of related genes in 1‐year‐old healthy Megalobrama amblycephala . The bacterial strains included Lactobacillus plantarum , Lactobacillus fermentum , Enterococcus faecium , Bacillus velezensis , Paenibacillus polymyxa and Lactococcus sp. The fish were randomly divided into five groups: one group was fed a basal diet (control group), and the other groups were provided feed containing EMs at levels of 5, 10, 20 or 40 g/kg. The growth performance, gastrointestinal digestive enzyme activity and expression of the growth hormone (GH), GH receptor A (GHRA), GH receptor B (GHRB) and insulin‐like growth factor‐1 (IGF‐1) genes in the liver of M. amblycephala after 60 days of outdoor cage culture were analysed. The weight gain rate for M. amblycephala significantly increased when EM was added to the feed, and the 10 g/kg EM group had the greatest weight gain, which was 7.34% higher than that of the control group; this group also presented the highest intestinal protease and lipase activities. Regarding hormone levels, GH, GHRA, GHRB and IGF‐1 expression levels were highest in the 10 g/kg EM group. Additionally, EM addition significantly improved lipoprotein metabolism in the liver, resulting in a decrease in low‐density lipoprotein levels and an increase in high‐density lipoprotein levels. The results of this study suggest that EM supplementation in feed improves the growth performance of M. amblycephala , reduces the risk of fatty liver and affects the expression of growth genes.
Zhu et al. (Thu,) studied this question.