The vitamin B12-producing ability of the intestinal microflora of freshwater fish

Abstract

The vitamin B₁₂-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 B₁₂), 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 B₁₂-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 B₁₂ 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 B₁₂ production in the intestinal tract of freshwater fish.