A comparison of the properties of the becterial flora present in the digestive tracts of fish, red sea bream snapper and crimson sea bream, which were fed with three different diets (F-, C- and S-diet), was carried out.
The results were summarized as follows:
(1) Although there was a little variation in the numbers of bacteria in the digestive contents among the three dietary groups of fish, in morphological and biochemical properties the bacteria isolated resembled one another in spite of difference of diet.
(2) The majority of strains isolated from environmental sea water were different from those isolated from fish in the abilities to produce indol and to hydrolyse starch and casein. A dominant group having a certain definite property was not found among the strains isolated from C-diet.
(3) The growth of bacteria isolated from fish was not affected by bile or low pH value, while that of bacteria isolated from sea water and diet was affected.
It is suggested that the flora in the digestive tract are limited to only a few bacterial groups, since the environmental conditions in the digestive tract are so severe as to exclude the great majority of exotic bacteria.