Effects of dietary host-associated Lactococcus lactis on growth performance, disease resistance, intestinal morphology and intestinal microbiota of mandarin fish (Siniperca chuatsi)

Abstract

This study was conducted to evaluate the effects of dietary host-associated Lactococcus lactis 3-c-18 supplementation on the growth, serum biochemical indices, liver and intestine health, intestinal microbiota, and Aeromonas hydrophila resistance in mandarin fish (Siniperca chuatsi). Mandarin fish were fed with four experimental diets containing 0 CFU/kg−1 (CR), 0.95 × 108 CFU/kg−1 (R1), 0.86 × 109 CFU/kg−1 (R2), and 0.91 × 1010 CFU/kg−1 (R3) L. lactis 3-c-18 for ten weeks. The results showed that fish fed the R1 and R2 diets exhibited a higher percentage weight gain and lower feed conversion ratio than fish fed the CR and R3 diets. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity were significantly decreased by dietary L. lactis 3-c-18 supplementation. Glucose (GLU), total cholesterol (TCHO) and malondialdehyde (MDA) levels were significantly depressed by the inclusion of L. lactis 3-c-18 in the diet, however, serum CAT levels were enhanced by L. lactis 3-c-18. The hepatic and intestinal morphology of mandarin fish fed L. lactis 3-c-18 was better than the control group and the relative abundances of Spirochaetes and Proteobacteria in the mid-gut were significantly increased by dietary L. lactis 3-c-18 supplementation. Meanwhile, Linear discriminant analysis Effect Size (LEfSe) analysis showed that L. lactis 3-c-18 increased the abundance of Lactococcus in the intestines of mandarin fish. The challenge test demonstrated that fish in groups fed with L. lactis 3-c-18 diets had a lower mortality rate compared to the control group. In conclusion, L. lactis 3-c-18 can have beneficial effects on growth performance, liver and gut health, A. hydrophila resistance, and intestinal microbial diversity of mandarin fish. However, high levels of L. lactis 3-c-18 in the diet may reduce these beneficial effects. Based on the results of the current study, the recommended dose of L. lactis 3-c-18 in mandarin fish feed is approximately 1 × 108 CFU/kg.