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.
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.