Abstract:The present study aimed to assess the effect of Bacillus licheniformis on the growth, intestinal digestive enzymes activity, non-specific immunity and resistance against Aeromonas salraonicida in the fat greenling (Hexagrammos otakii). A total of 270 H. otakii with an average initial body weight of (22.0±2.0) g/tail were randomly allocated to three groups (the control group and two experimental groups with different B. licheniformis levels) with three parallels per group and 30 fish per parallel. Fish in the control group were fed a basal diet consisting of albumen, and the ones in the two experimental groups were fed basal diets supplemented with 5×107 (0.5%) or 1×108 CFU/g (1.0%) B. licheniformis, respectively. After 50 days, fish were infected with A. salraonicida, and the cumulative mortality rate was determined within 14 days. The specific growth rate was found to be significantly higher in fish fed diets containing B. licheniformis when compared with the control group (P<0.05). Furthermore, the activities of SOD, CAT, and T-AOC in the serum of H. otakii in the experimental groups were significantly increased compared with the control group (P<0.05). Conversely, the MDA levels in the experimental groups were decreased compared with the control group (P<0.05). The GSH-Px activity in the 1.0% B. licheniformis group was lower than that in the control group, but the activity in the 0.5% B. licheniformis group was higher than that in the control group. The activities of GS, MDH, and HK in the serum of fish in the experimental groups were increased compared with the control group (P<0.05). Compared with the control group, AST and ALT activities in the serum of fish in the experimental groups were decreased (P<0.05) and CHE and ADA activities were higher than those in the control group (P<0.05). The activities of trypsin, amylase and lipase in the intestines of fish in the experimental groups were increased to different degrees, with the highest activity observed in the 1.0% B. licheniformis group (P<0.05). The bacterial challenge test revealed that the 14 day cumulative mortality rate in the 1.0% B. licheniformis group was only 35.55% (P<0.05). The results obtained in the present study revealed that B. licheniformis can increase growth, activities of intestinal digestive enzymes, and non-specific immunity, as well as enhance resistance against A. salraonicida in H. otakii.
