Changes in Intestinal Flora of the Juvenile Eel, Anguilla japonica, After Beginning to Feed

Abstract

Changes in intestinal flora of the juvenile eel, Anguilla japonica, after beginning to feed were studied.
The juvenile eel just after being caught had no detectable bacteria in the intestines, but after beginning to feed, they always had 10⁶-10⁷ colony forming units of bacteria per gram of intestine with contents. When they were fed Tubifex sp. as an initial food, the composition of intestinal flora of the eel was as follows: Streptococcus, 33 %; Enterobacteriaceae, 43%; Aeromonas, 1 %; Plesiomonas, 15%; Acinetobacter, 1 %; Achromobacter, 4%; others, 2 %. This composition was similar to that of bacterial flora of Tubifex sp., that is, the bacteria in the intestines seemed to be simply transferred from Tubifex sp. to the eel. When the food for the eel was changed to the mixture of Tubifex sp. and formula food, the intestinal flora of the eel consisted of Streptococcus (13 %), Enterobacteriaceae (50%), Aeromonas (9 %), Plesiomonas (11 %), Acinetobacter (6 %), Achromobacter (7 %) and others (4 %). When the food was completely changed to formula food, the following was the intestinal flora: Streptococcus, 25%; Enterobacteriaceae, 12 %; Aeromonas, 16%; Acinetobacter, 17 %; Achromobacter, 4 %; others, 15 %. As a result, the composition of the intestinal flora of the eel had a tendency that the percentage of Enterobacteriaceae decreased, and those of Aeromonas and Acinetobacter increased, with the change of food from Tubifex sp. to formula food.