A REVIEW ON THE EFFECTS OF PROBIOTICS AND PREBIOTICS AS THE ANTIBIOTIC REPLACERS IN JAPANESE EEL Anguilla japonica

Japanese eel, Anguilla japonica, is one of the most important cultured fish species in East Asia. Along with the fast expansion and intensification of Japanese eel aquaculture, emergence of large varieties of pathogenic diseases are considered as limiting impediments. On the other hand, the excessive treatments of antibiotics has caused the appearance of bacterial resistance strains. In this regard, three experiments were conducted to identify probiotics such as Bacillus subtilis, Lactobacillus plantarum and Bacillus licheniformis with or without prebiotics such as mannan oligosaccharide (MOS), β-glucan and fructo oligosaccharide (FOS) as effective antibiotic replacers. Results for the first experiment indicated that based on growth performance, immunological parameters, gut morphology and disease resistance, B. subtilis at 10⁸ and 10⁷ CFU/g diet could be a more effective source of probiotic compared to L. plantarum in Japanese eel. In the second experiment, comparing different concentrations of B. subtilis (0, 0.5×10⁷ and 1×10⁷ CFU/g diet) with MOS and β-glucan (0 and 5 g kg^-1 diet) prebiotics showed that combination of B. subtilis+ MOS (0.5×10⁷ CFU/g+5 g kg^-1 diet) resulted in a better growth performance, immunological status, gut morphology and disease resistance. In the third experiment, comparison of Bacillus subtilis and Bacillus licheniformis with prebiotics such as MOS or FOS was performed. Results indicated that of B. subtilis with MOS or FOS could have beneficial effects on growth performance of Japanese eel. Therefore, it could be concluded that probiotics have the potential as antibiotic replacers while enhancing growth performance and immunity. In addition, application of selective strains of probiotics for specific fish seems to be vital in order to maximize the effectiveness.