Abstract
The influences of cooling on the intestinal microflora of the Japanese eel and on the persistence of an administered virulent strain of Aeromonas hydrophila A10 in the intestine of the eel were investigated. A change in the intestinal microflora was commonly observed in spite of differences in the length of the treatment (cooling). After being placed in chilled water (10°C lower than control temperature) for 2 hours and for 12 hours, Streptococcus increased at first in proportion to the majority of the intestinal microflora, while Aeromonas decreased. Two or three days after the treatment, the relation between them was reversed, i. e., Aeromonas increased and Streptococcus decreased. During repeated treatments, Streptococcus was predominant and decreased four or five days after the first treatment, but Aeromonas was rarely isolated. There was no difference in the temperature ranges for growth of the isolates from the intestine of the eel, they were between 14 and 45°C. The persistence of the administered A. hydrophila A10 was prolonged in the eels stressed with temperature decrease, but the infection was not established. From these results the authors concluded that the physiological function of the eel was changed by the rapid decrease of the water temperature and it caused the fluctuation of the intestinal microflora. This physiological change might affect an exogenous pathogen in the intestine.
