The histopathological observation was made on diseased elvers and anguilletes infected with Edwardsiella tarda. Diseased fish showed a swelling accompanying with minute hemorrhages and often perforation either in the liver or kidney region of the trunk. Histopathologically the disease could be classified in two forms as in the case of big eels. 1) Interstitial nephritis: In this form the degree of the suppurative reaction was weak as compared with the case with big eels. In the early stages of the disease small necrotic lesions appeared in the hematopoietic tissue of the kidney. In the advanced stages necrotic lesions developed into large ulcers. In the ulcerative lesions bacterial multiplication and liquefaction of the involved tissues were very marked. Metastatic lesions were common in the various organs. 2) Hepatitis: In anguilletes, a large liquefactive lesion appeared in the liver in the advanced stages. In elvers small abscesses were observed in the liver in the early stages. In the advanced stages a large ulcerative abscess was formed in the liver, and suppurative peritonitis and omentitis spreaded. The spleen, thymus and hematopoietic tissues were hyperplastic.
In the late autumn of 1968 and 1970, an epizootic occurred among yellowtails, Seriola quinqueradiata, in culture farms in Kochi Prefecture. Affected fishhad large abscesses with hemorrhagic borders in th body surface. An etiological agent was isolated from spleen and kidney of moribund yellowtails. The isolated organism was gram-negative, nonsporning rods with polar flagella, and usually 0.5 to1.0 by 1.5 to 4.4μ in size. On nutrient agar colonies developed within 24hours at 25deg;C. The optimal temperature for the growth was about 25deg;Cto 30deg;C. Nogrowth occurred at 5deg;C or 37deg;C. Oxidase and catalase were positive. Glucose, levulose, mannose, galactose and glycerol were attacked by oxidation, whereas trehalose, erythritol, adonitol, mannitol, sorbitol and inositol were not attacked. Indole, hydrogen sulfide, nitrate, methylred test, gelatin liquefaction, VP and LV reaction were negative. The organism produced diffusible fluorescin, particularly in iron-deficient media. It was sensitive to chloramphenicol, oxytetracycline, tetracycline, kanamycin, erythromycin, colistin, nalidixic acid and polymixin B. The organism was therefore identified asPseudomonas putida.
In 1975, a new vibriosis occurred in eels (Anguilla japonica and A. anguilla) cultured in Tokushima Prefecture in Shikoku Island of Japan. The disease prevailed in brackish water ponds (Cl-2-6‰) during summer and early autumn, when the water temperature of culture ponds ranged from 20°C to 30°C. The causative Vibrio seems to be classified as Vibrio anguillarum B type (V. anguillarum f. anguillicida) suggested by NYBELIN (1935), but this type can no longer be included in V. anguillarum listed in Bergey's Manual of Determinative Bacteriology 8th ed. Assuming that V. anguillarum B type is independent of V. anguillarum, the present isolate is classified as V. anguillicida BRUUN and HEIBERG 1932. On the other hand, in comparison with Vibrios listed in Bergey's Manual the characteristics of the present isolate are closely resemble to those of V. fischeri. Thus, further investigation are necessary before the taxonomic status of the present Vibrio is determined.
In the previous report biochemical characteristics of an isolate from a vibriosis in eels were presented and the taxonomic status of the isolate was discussed, though a definite conclusion could not be drawn. In this paper, physiological characteristics and pathogenicity of the organism are described. The experimental results are summarized as follows. 1) Effects of sodium chloride, temperature and pH on the growth of the organism: It grew in nutrient broth at NaCl 0.1-4% (optimum range 1-2%), and in peptone water at temperatures from 18°C to 39°C (optimum 30-35°C) and at pH 6-10. 2) Pathogenicity to eel (Anguilla japonica) and mouse: The organism injected intramuscularly killed eels at 18, 20 and 26°C, but not at 15°C. It also killed mice. These results coincide with the fact that the vibriosis due to the organism prevails mainly in brackish-water ponds and at the water temperatures above 18°C.
The authors made a morphological observation of a copepoda belonging to the genus Salmincola, obtained from yearing Yamame, Oncorhynchus masou reared in the Masutani Trout Culture Farm at Tashiro in Gunma Prefecture. The species was identified with S. californiensis (DANA, 1953) KABATA, 1969 following to KABATA'S revision of the genus Salmincola. Principal structures of appendages of the adult female were almost completely coincided with the KABATA'S discription but some differences were found in the adult male (KABATA et al. (1973)).
Populations of rainbow trout (Salmo gairdneri) in freshwater ponds in Japan are often attacked by vibriosis. The causative bacterium was identified as Vibrio piscium var. japonicus by HOSHINA in 1957. But the species is now considered as a synonym of V. anguillarum. From 1973 to 1976, the present authors studied the biochemical characteristics of 22 strains which were isolated from diseased rainbow trout cultured in ponds in various districts of Japan. All the strains differ from V. anguillarum in their properties that they show poor growth on standard nutrient agar and fail to decompose arginine, to ferment mannose and mannitol, and to produce indole. Although further studies are needed to determine the exact taxonomic position of the isolates described here, the authors gave a tentative name of Vibrio sp. RT group to the 22 strains for the convenience of future studies.
Observations were made with the scanning electron microscope (SEM) on two groups of microsporidian spores collected from the Ayu, Plecoglossus altivelis, fixed in 10% formalin. One group of spores were obtained from fry kept in salt water after artificial spawning and the other from adults cultured in fresh water. The spores collected were refixed with 2% KMnO4, dried in aceton series, evapolated with carbon and gold, and examined with SEM. The observations clearly demonstrated that the both groups of spores were the same in shape, size and surface structure, and identified as Glugea plecoglossi TAKAHASHI et EGUSA.