The present authors have been studing on vibriosis (Vibrio anguillarum infection) in ayu (Plecoglossus altivelis) from the viewpoint of control. Prior to the main experiment, several experimental challenge methods were examined in oredr to establish a reproducible artificial challenge system of vibriosis. This paper deals with the validity of the artificial challenge system by intramuscular inoculation and a practical application of this system to testing the efficacy of oral-administered drugs for ayu. The results are summarized as follows. 1) The minimal lethal dose of a strain of Vibrio anguillarum used in this study proved to be 8.75 cells or 1×10 mg-8 in wet weight per 100 g of body weight of ayu. 2) A clear correlation was observed between inoculation dose and mean time to death in the challenge system tested. 3) A satisfactory result was obtained in the experiment of drug efficacy, and the intramuscular inoculation was found applicable to tests for drug efficacy.
A milky condition in smoked coho salmon was observed at a food processing factory in Hokkaido, Japan. The incidence of milky condition was 7.8-11.7 percent of the fish after completion of the smoking process. This condition was due to an infection of the raw salmon, imported from Canada with a myxosporidian parasite identified as Henneguya salmonicola by its characteristic spores.
The first stage larvae of Philometroides carassii(ISHII, 1931) NAKAJIMA et EGUSA, 1977 which were released from the gravid females had very delicate bodies with adhesive sharp pointed tails. They extended and constracted actively in live but were always bent into a siclke-shape when died. They survived in water for seven days at 15°C, five days at 25°C, four days at 2-5°C and several hours at 37°C. Drying, freezing, heating and irradiating of ultraviolet rays were very effective to kill them. The larvae were killed instantly when water was evapolated or freezed. Heated larvae died within 18-20 minutes at 40°C, 8-9 minutes at 45°C and a minute at 50°C, and larvae were killed, within 6-8 minutes by irradiation of 2, 000μW/cm2, 14-16 minutes by 1, 000μW/cm2, 43-45 minutes by 400μW/cm2. Larvicidal effect of several disinfectants and anthelmintics were examined in vitro. One ppm of Acrinol, Benzetonium chloride and Sodium dichloroisocyanurate and 10 ppm of Bithionol and Dithiazanine iodide was demonstrated to kill larvae within three days.
Quantitative and qualitative investigations of intestinal microflora were made on healthy and diseased eels collected from culturing ponds in Yoshida, Shizuoka Prefecture. The whole intestine of each eel was homogenized in sterile 0.85% NaCl solution. Tenfold dilutions were prepared and 0.1 ml of which was inoculated on the surface of nutrient agar (Difco). Plate cultures were incubated for five or seven days at 25°C and colonies were counted. Every colony within a given area of the plate of suitable dilutions was subcultured for identification. The numbers of viable bacteria per gram of intestinal tract with contents in healthy eels were ranged from 10 to 109 through the year. The percentage of Aeromonas spp. (mostly A. hydrophila) was relatively higher in winter, while that of Enterobacteriacea was higher from spring to fall. Vibrio sp. appeared only in October. Streptococcus sp. was always present 20% to 80% in the intestine of fed eels. Viable counts of intestinal bacteria of diseased eels were 10 to 106 higher than those of the healthy ones (Fig. 1 and Table 4). The percentage of A. hydrophila tended to be higher (Fig. 2), especially in the case of red disease. Moreover, virulent strains from eels suffered from red disease were greater in number than those from healthy ones or eels infected with Edwardsiella tarda (Table 5).
The larvae of Digramma alternans were found on the Japanese dace, Tribolodon hakonensis inhabited Hidaka-horobetsu River in Hokkaido. This is a first finding of D. alternans in fish inhabited rivers in Japan. It was assumed that the first intermediate host (copepods) and the final host (birds) inhabit the swamps which are located around the mouth of the river and lead to it.
The present study was carried out to reveal the characteristics of organism responsible for socalled vibriosis prevailing in cold-water season among cultured red sea bream, Pagrus major. Nine strains obtained from diseased red sea bream in some culture farms in Nagasaki Prefecture in the mid-winter of 1977 were submitted to the morphological, biochemical and physiological characterization. All the strains were gram-negative, nonsporning short rods with one polar flagellum.Cytochrome oxidase and catalase reactions were all positive. Glucose was fermented with no gas production by these strains. In consideration of these characteristics, the present isolates were tentatively ascribed to Vibrio, although many differences were observed among these strains in the other characteristics. On the basis of the decarboxylation of lysine, arginine and ornithine, it was possible to divide these stains into three groups. In general, the temperature of 20-27°C, the NaCl concentration of 2-3%and the pH of 6-8 were optimal for the growth in peptone water. Future taxonomic or genetic studies will be necessary to define the present isolates accurately.