THE VITAMIN-B12-PRODUCING ABILITY OF THE INTESTINAL MICROFLORA OF FRESH-WATER FISH

The vitamin B-12-producing ability of the intestinal microflora in six freshwater fishes (Japanese eel, carp, goldfish, ayu, tilapia and channel catfish) was examined. Aeromonas, Enterobacteriaceae and Pseudomonas were widely distributed in the intestinal tract of the freshwater fish examined. An obligate anaerobe, Bacteroides type A, predominated in carp and tilapia (which do not require dietary vitamin B-12), along with goldfish and ayu. However, this bacterium was not detected in fish which require dietary vitamin B12 (the eel and channel catfish). In general, the vitamin B-12-producing ability of obligate anaerobes including Bacteroides type A, other Bacteroidaceae and Clostridium was much higher than aerobes and facultative anaerobes. It also was found that there is a close relationship between the amounts of vitamin B-12 and viable counts of Bacteroides type A in the intestinal contents of carp. These results strongly suggested that the Bacteroides type A is closely involved in vitamin B-12 production in the intestinal tract of freshwater fish.