The Effects of Two Dietary Synbiotics on Growth Performances, Hematological Parameters, and Immune Responses in Japanese eel, Anguilla japonica

Abstract

The effects of two dietary synbiotics; Bacillus subtilis with mannan oligosaccharides and Enterococcus faecium with fructooligosaccharides were evaluated for 8 weeks on growth performances, hematological parameters, and immune responses in Japanese eel, Anguilla japonica. Six experimental diets consist of a basal diet (CON), an antibiotic diet containing CON with 5 g/kg of oxytetracycline (OTC), and 4 synbiotic diets; Bacillus subtilis at 106 or 107 CFU/g plus 5 g/kg mannan oligosaccharides (BS6 and BS7) and Enterococcus faecium at 106 and 107 CFU/g plus 5 g/kg fructo oligosaccharides (EF6 and EF7). Eighteen tanks of fish averaging 6.00 ± 0.07 g (mean ± SD) were randomly assigned into six experimental diets in 3 replicates. Weight gain (WG) and specific growth rate (SGR) of fish fed BS6 and BS7 diets were significantly higher than those of fish fed CON and OTC diets (P<0.05), however, there were no significant differences among those of fish fed BS6, BS7, EF6, and EF7 diets. WG and SGR of those of fish EF6 and EF7 were significantly higher than those of fish fed CON diets (P> 0.05). Feed efficiency of fish fed BS6, BS7 and EF6 diets were significantly higher than those of fish fed CON and OTC diets, however, there were no significant difference among fish fed BS6, BS7, EF6, and EF7; among those of fish fed EF7 and CON; and among those of fish fed OTC and CON (P> 0.05). Protein efficiency ratio of fish fed BS6, BS7, EF6, and EF7 diets were significantly higher than those of fish fed CON and OTC diets (P < 0.05). Hematological parameters including total protein and glucose were not significantly different among those of fish fed all experimental diets. Average myeloperoxidase activity of fish fed BS7 diet were significantly higher than those of fish fed CON, OTC, BS6, EF6, and EF7 diets (P < 0.05). After the challenge test by Vibrio anguillarum, average cumulative survival rates of fish fed BS7 were significantly higher than those of fish fed CON diet, however, there were no significant differences among those of fish fed OTC, BS6, BS7, EF6, and EF7 diets (p > 0.05). These results suggest that four synbiotics; BS6, BS7 (Bacillus subtilis at 106 or 107 CFU/g plus 5 g/kg mannan oligosaccharides) EF6, EF7 (Enterococcus faecium at 106 and 107 CFU/g plus 5 g/kg fructo oligosaccharides) could be the potential feed additive and antibiotics replacer in Japanese eel feeding and farming. The results also indicated that B subtilis plus mannan oligosaccharides may be more effective to compare with Enterococcus faecium plus fructo oligosaccharides.