The aim of this study was to determine the beneficial effects of Lactobacillus plantarum , Azotobacter vinelandii and its exopolysaccharides on fish health and their suitability for in vivo fish aquaculture. Ten lactobacillus strains were isolated from the intestines of frozen marine fresh water fish. Lactobacillus, A. vinelandii and its exopolysaccharide alginate were tested for in vitro antagonism to common fresh water fish pathogens identified as Aeromonas hydrophila and Escherichia coli, and human pathogenic microorganisms. The highest antagonistic Lactobacillus was tentatively named as Lactobacillus plantarum. L. plantarum and A. vinelandii proved resistant to gastrointestinal fluid, survived at pH 2, 2.5 & 3, and good adhesion to fish intestine. However, L. plantarum was more active than A. vinelandii and co-culture with exopolysaccharides stimulated L. plantarum for more viability, adhesion and salinity tolerance. After drying process of feed supplemented with L. plantarum and A. vinelandii, their counts slowly decreased by the time; A. vinelandii was more sensitive than L. plantarum. Both the probiotic organisms still viable up to 1 year in the feed stored at 4oC. L. planetarium lived at 25oC up to 2 months, while A. vinelandii started to loose viability after 1 month. Although both candidate bacteria showed good survival in cultures supplemented with alginate from A. vinelandii and NaCl up to 4-6%, L. plantarium was more tolerant than A. vinelandii. In conclusion, L. plantarum, A. vinelandii and alginate produced by A. vinelandii have potential applications as probiotics and prebiotic to fresh and marine water fish farms.
Key words: Lactobacillus plantarum, Azotobacter vinelandii, probiotic, prebiotic, exopolysaccharides, Oreochromis niloticus
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