養殖ウナギのChondrococcus columnaris感染症に関する研究-I : 養殖ウナギから分離されたC. columnarisの細菌学的性状と病原性

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Since 1966, gill disease has been associated with serious mortality of pond-cultured eels during the summer months in many eel farms in Shizuoka prefecture. The disease was characterized by partial or extended losses of gill filaments and the occurrence of yellowish colonies of Chondrococcus-like bacteria on the gill surface. The cultures isolated from gill lesions were long flexible Gram-negative rods, which showed the movements and columnar formation peculiar to Chondrococcus columnaris. The formation of fruiting bodies and the production of microcysts were observed in the cultures maintained by BORGs method. The organism was therefore identified as Chondrococcus columnaris (DAVIS) ORDAL and LUCKER (1944). The biochemical characteristics of the organism (Table 2) were in full accord with those of C. columnaris isolated from Japanese loaches. The organism was occasionally isolated from skin lesions and the kidney of diseased fish. Eels were experimentally exposed to five strains of C. columnasis by means of pouring the broth cultures on the gill surface. Two preliminary experiments suggested that the pathogenicity of the organism might differ markedly with strains (Table 3). The same was perceived in the following experiments using three other strains (Table 4). In these experiments use was made of well-fed, fat and starved, thin fish, in which the opercula were removed and the surface of the gills on one side was lightly brushed with a tooth-brush prior to the experimentation. In the three strains typical yellowish colonies appeared on the gill two to three days after the exposure, and parts of the gill filaments began to degenerate and finally gill lesions of the same type as those that naturally occur were produced (Plate). Occasionally colonies once developed on the gill disappeared in course of time. Mechanical injuries on the gill surface did not necessarily facilitate the infection of the organism. The fatality of the organism to the eel varied considerably with the strain. As compared with fat fish, starved, thin fish seemed to be much resistant to the attack of the organism.
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養殖ウナギのChondrococcus columnaris感染症に関する研究-I : 養殖ウナギから分離されたC. columnarisの細菌学的性状と病原性

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