Comparative evaluation of dietary probiotics Bacillus subtilis WB60 and Lactobacillus plantarum KCTC3928 on the growth performance, immunological parameters, gut morphology and disease resistance in Japanese eel, Anguilla japonica

The current experiment was conducted to evaluate and compare the efficacy of two different probiotics Bacillus subtilis WB60 and Lactobacillus plantarum KCTC3928 in diet of Japanese eel, Anguilla japonica. Seven experimental diets were formulated to contain no probiotics (CON), three graded levels of B. subtilis at 106 (BS1), 107 (BS2), 108 (BS3) and L. plantarum at 106 (LP1), 107 (LP2), 108 (LP3) CFU/g diet. Twenty fish averaging 8.29 ± 0.06 g were distributed in to 21 aquaria and were randomly assigned to one of the experimental diets in triplicate groups. Average weight gain (WG), feed efficiency (FE), and protein efficiency ratio (PER) of fish fed B. subtilis at 107 (BS2) and 108 (BS3) CFU/g diet were significantly higher than those of fish fed other experimental diets (P < 0.05). Nonspecific enzymatic activities including lysozyme, superoxide dismutase (SOD), myeloperoxidase (MPO) from fish fed B. subtilis at 107 (BS2) and 108 (BS3) CFU/g diet were detected to be significantly higher than that from fish fed CON diet (P < 0.05). Whereas, level of intestine glyceraldehyde-3-phosphate dehydrogenase (GAPDH), heat shock protein 70, 90 (HSP70, 90) and immunoglobulin (IgM) from fish fed B. subtilis at 107 and 108 CFU/g diet were recorded to be significantly higher than those of fish fed other experimental diets (P < 0.05). Parameters for intestinal morphology and histology suggested a healthier gut for the fish fed108 (BS3) CFU/g diet as compared to other treatment groups. Whereas, results from the disease challenge test with bacteria Vibrio angulillarum showed significantly lower survival rate for fish fed CON diet than those of fish fed other experimental diets. Therefore, these results indicated that oral supplement of B. subtilis at 108 (BS3) CFU/g diet could be a more effective source of probiotic compared to L. plantarum in Japanese eel.