Ecology of Vibrios in Estuarine Region of Seto Inland Sea Distribution of Some Diarrhenogenic Species

Distribution of diarrhenogenic species of genus Vibrio in estuarine area of Ohta River, Hiroshima, and Asahi River, Okayama, was investigated. Diarrhenogenic vibrios, such as Vibrio parahaemoly-ticus, V. fluvialis or NAG vibrio, inhabit in estuarine region. Because the former two vibrios are slightly halophilic, they cannot survive in fresh water. However, the number of V. parahaemolyticus detected in brackish water area of the river was much more than that of sea region. In brackish water area, the salinity was lower than optimal concentration for the vibrio because sea water was mixed with fresh water, but nutrient salts content, such as phosphate and nitrogen compounds, was higher than that of sea region. These nutrient salts seemed to stimulate a growth of the vibrios in estuarine region. The number of V. fluvialis was variable and in some sampling points, its number was comparable to the number of V. parahaemolyticus. NAG vibrio was also widely distributed in the estuarine region investigated, but the number was fewer than that of V. parahaemolyticus or V. fluvialis.