It is a well-known fact that some of B vitamins are synthesized by intestinal bacteria in mammals. Knowledge on fish, however, is still lacking. The present study was planned to see the production of nicotinic acid, pantothenic acid and vitamin B₁₂ by intestinal bacteria of carp, Cyprinus carpio. Bacteria in the intestinal contents were incubated in different culture media and the vitamins were estimated periodically by the microbiological methods. The results ob-tained are as follows.
1. Production of nicotinic acid is inconsistent according to the culturing conditions (Fig. 1).
2. Pantothenic acid shows the increase only after a prolonged culture period (Fig, 3).
3. Unlike the above two vitamins, vitamin B₁₂increases rapidly and markedly, especially at a higher temperature (Fig. 5).
4. Effect of the pH value of medium on the production of nicotinic and pantothenic acids is not significant (Figs. 2 and 4).