Impact of supplementary Lactobacillus casei K17 on growth and gut health of largemouth bass Micropterus salmoides

Micropterus salmoides is one of the most economically valuable fish species in China. Currently, information in the effect of probiotics-supplemented feed on M. salmoides is rare. Present study investigated the impact of supplementary Lactobacillus casei K17 with six treatments on growth performance, gut digestion, absorption and non-specific immune, and gut bacterial biota and metabolomics of M. salmoides. A total of 450 M. salmoides (114 day of age, average 33.0 ± 0.5 g) were randomly allocated into six groups for a 69-day rearing experiments. M. salmoides was given commercial feed supplemented with: 1) live L. casei K17 (1 × 109 CFU/g), 2) live L. casei K17 protected by skim milk powder (10 %), 3) heat-killed dead L. casei K17, 4) its fermentation supernatant, 5) skim milk powder (10 %), and 6) normal saline (0.85 % NaCl), designated as LB, MB, DB, FS, MG, and SG, respectively. MB and DB diets significantly increased body weight and growth rate, but decreased feed conversion ratio of M. salmoides (p