Comparison of Intestinal Microflora between Healthy and Diseased Pond-cultured Eels

Quantitative and qualitative investigations of intestinal microflora were made on healthy and diseased eels collected from culturing ponds in Yoshida, Shizuoka Prefecture. The whole intestine of each eel was homogenized in sterile 0.85%NaCl solution. Tenfold dilutions were prepared and 0.1 ml of which was inoculated on the surface of nutrient agar(Difco). Plate cultures were incubated for five or seven days at 25°C and colonies were counted. Every colony within a given area of the plate of suitable dilutions was subcultured for identification. The numbers of viable bacteria per gram of intestinal tract with contents in healthy eels were ranged from 10 to 10^9 through the year. The percentage of Aeromonas spp. (mostly A. hydrophila) was relatively higher in winter, while that of En:erobacteriacea was higher from spring to fall. Vibrio sp. appeared only in October. Streptococcus sp. was always present 20% to 80% in the intestine of fed eels. Viable counts of intestinal bacteria of diseased eels were 10 to 10^6 higher than those of the healthy ones (Fig. 1 and Table 4). The percentage of A. hydrophila tended to be higher (Fig. 2), especially in the case of red disease. Moreover, virulent strains from eels suffered from red disease were greater in number than those from healthy ones or eels infected with Edwardsiella tarda (Table 5)