In the previous study (HORIUCHI et al., 1980), the species-specificity of direct immunofluorescence (IF) and the specific reactivity of labeled antibody on impression preparation from an artificially infected eel were confirmed. In this study, the direct IF for rapid diagnosis of edwardsiellosis in eels was evaluated on field cases. Fifty two cases of 25 outbreaks of bacterial disease in 19 eel farms were examined during the period from December, 1978 to February, 1980 (Table 1). Staining acetone-fixed impression preparations of liver and/or kidney with 4 units of FITC-labeled anti-E. tarda rabbit IgG was made, as well as cultures on nutrient agar. The preparations were examined with fluorescence microscope under UV excitation system and the pure cultures obtained were identified by their morphological and biochemical properties. The results obtained by direct IF were compared with culture results. Of the 52 cases, 43 cases were positive and 9 negative by direct IF. The results of direct IF coincided with the culture results of E. trada (Table 2). In 12 cases of 43 cases where direct IF results were positive, both E. tarda and Aeromonas sp. were isolated. In 9 cases where direct IF results were negative, Vibrio sp. or Aeromonas sp. was isolated. The above data indicated that we could employ direct IF on impression preparation for the rapid and accurate diagnosis of edwardsiellosis in eels.
In the previous report (MUROGA et al., 1979), a vibrio isolated from diseased ayu (Plecoglossus altivelis) was classified as non-cholera vibrio (non-agglutinable vibrio) on the basis of its morphological, biochemical and genetical characteristics. In this paper, physiological characteristics and pathogenicity of the organism are described. The experimental results are summerized as follows. 1) Effect of NaCl, temperature and pH on the growth of the organism : It grew in broth (1%peptone)at NaCl 0-5%(optimum 1%), at temperatures 15-42°C(optimum 37°C), and at pH 7-10(optimum 8), respectively. 2) Survival in waters:At 25°C the organism perished in distilled water within a few hours, but it survived 320 days in freshwater, 0.85%NaCl solution, Ringer solution, Ringer-Locke solution, sea water, and diluted sea water. At 2°C, however, it became extinct in 8 days in freshwater. 3) Pathogenicity:Ayu infected by immersion method died at 21°Cand 26°C, but not at 16°C.The organism killed eels(Anguilla japonica)and mice.
Nutritional myopathy occurred in yellowtail (Seriola quinqueradiata) reared with raw food fish which were rancid during stock with a freezer in Amami Ooshima Island in the winter of 1973. The diseased fish manifested extremely slender bodies and jelly-like muscles. The striated muscle fibers histopathologically underwent various alterations; simple atrophy, clowdy swelling, vacuolar degeneration, atrophy accompanying separation of a salcoplasmic mass and necrosis without an invasion of microorganism, regeneration of muscle fibers and inflammatory responses. The alterations of muscle fibers caused mascular atrophy and compensative production of the interstitial adipose tissue. A lot of masses of macrophages phagocytizing ceroid were formed around arteriolae in the adipose tissue. The muscular atrophy involved the red musculature in the mild case and both the red and white musculature were atrophied in the advanced case. In both cases a lot of masses composed of macrophages phagocytizing ceroid, lipoprotein, hemosiderin and melanin appeared in the liver, the spleen and the renal hematopoietic tissue.
A trematode was frequently found in the stomach of the flatfish larvae under culture in the Niigata Prefectural Center of Cultural Fisheries. Preliminary culture experiments using different kinds of zooplanktons as feed were done to know the source of infection of the trematoda. The trematoda occurred frequently in the larvae given marine copepods collected from the coast sea, but was never found in the larvae given cultured Artemia and Tigriopus. In most infected fishes the number of the trematoda per fish was 5 to 7. The trematoda was indentified as a member of the genus Uteroversiculus.
An epizootic occurred among pond-cultured ayu, Plecoglossus altivelis, in Tokushima Prefecture in 1978. The symptom was characterized by both exophthalmos and subcutaneous hemorrhage. One species of bacterium was purely isolated from all these diseased fish, and submitted to characterization tests and pathogenicity tests with healthy ayu and eel, Anguilla japonica. Putting the results together, the etiological agent of the disease was identified as Aeromonas hydrophila subsp. hydrophila. This is the first record of A. hydrophila infection in pond-cultured ayu in Japan.
A parasitic copepoda was found on the epidermis of larval fish of red sea bream (Pagrus major) of 7.2-11.3mm long, 14-20days after hatching during artificial rearing. From the morphological observation, the parasite is considered as one of the Ergasilus sp. The present work is the first report on the parasitism of Ergasilus sp. on red sea bream. Since only a small number of fish among many were found to be parasited with the copepoda, the parasite does not seem to give serious damage for rearing the red sea bream.
An examination of Gyrodactylus infestations of cultured eels in Japan has revealed that Gyrodactylus nipponensis OGAWA et EGUSA, 1978 was parasitic on the Japanese eel, Anguilla japonica at 19 culture ponds in Chiba, Shizuoka, Tokushima and Miyazaki Prefectures and on the European eel, A. anguilla at 3 ponds in Tokushima Pref., while G. anguillae ERGENS, 1960 was found on A. anguilla at 2 ponds in Shizuoka Pref. There seems no difference in intensity of infestation of G. nipponensis between the two species of eels. The intensity attained to 20, 000 parasites/fish in A. japoinca of 45 cm in body length. The infestation of G. anguillae is the first record in Japan; G. anguillae is redescribed here. It is natural to consider that G. nipponensis was formerly the only gyrodactylid of A. japonica in Japan, since the eel has been found infested with G. nipponensis only. According to our opinion, G. anguillae was introduced with the host fish, A. anguilla from France, while G. nipponensis was, in some cases, parasitic on A. anguilla after the introduction of A. anguilla into Japan. No evidence was obtained that G. anguillae had settled at A. japonica-culturing ponds in Japan. The authors disagree with GOLOVIN (1977) on that G. anguillae was introduced into U.S.S.R. from Japan with the host fish, A. japonica.