Ecological Studies of Fish Pathogenic Bacteria in Eel Farm—I:Isolation of Aerobic Bacteria from Pond Water

概要

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Pond water of eel farms in Yoshida, Shizuoka Prefecture was examined for the presence of fish pathogenic bacteria, especially for Aeromonas spp. and Edwardsiella tarda. One-tenth milliliter of a series of ten fold dilutions of pond water was spread over the surface of nutrient agar(Difco).Plate cultures were incuvated for 4 or 5 days at about 25°C and colonies counted. Every colonies within a given area of the plate of suitable dilutions was subcultivated for identification. The number of bacteria ranged from 102 to 105 cells/ml through the year, being at the maximum in September and at the minimum in January(Table 1 and Table 2). Aeromonads and enterobacteria were predominantly found in all samples. Aeromonads represented the majority in fall to spring and tended to decrease as the water temperature rose(Table 3 and Table 4). A total 232 aeromanads were consisted of 224 A. hydrophila and 8 A. punctata. Of 134 A. hydrophila and 5 A.punctata, which were injected to weatherfish for testing its pathogenicity, only 13 A. hydrophila proved able to kill fish without full(Table 6). Enterobacteria were classified to the rank of genus as follow:78 Citrobacter, 46 Enterobacter, 9 Edwardsiella, 4 Escherichia and 45 others(Table 5). While many eels found to be infected with Edwardsiela tarda (WAKABAYASHI et al.1973, 1975), pond water had rather few E. tarda.
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