The results of a taxonomical study of 50 Vibrio strains isolated from several fishes diseased; yellowtail (Seriola quinqueradiata), kampachi (Seriora purpurascens), red sea bream (Chrysophrys major), black sea bream (Mylio macrocephalus), amago (Oncorhynchus rhodurus f. macrostomus), ayu (Plecoglossus altivelis) and eel (Anguilla japonica), and allied reference 21 strains show that the fish pathogenic vibrios can be divided into three major groups. Group I, Vibrio anguillarum are also subdivided into three subgroups according to their source, whether host fish have been affected in sea water, estuarine water or fresh water. Group II including Vibrio sp. K-3 have a close relationship to Vibrio parahaemolyticus, but are distinguishable from group I, V. anguillarum. Group III isolated almost from red sea bream in winter, seem to be pathogenic in the season of low water temperature, and in connection with V. ichthyodermis. Comparing some characteristic features of each group, a diagnostic scheme useful for rapid identification is given.
In July 1977, a numerous number of akame (Liza akame) with skin ulcer had been observed in the estuary of the River Ashida in Fukuyama city (MUROGA, 1979). Diseased fish were infected with a caligid parasite. The parasite was identified as Caligus orientalis GUSSEV, 1951 from the results of detailed observation. Akame is a new host of this species.
MG-fungus, causative agent of mycotic granulomatosis incubated at 25°C on the FME agar containing 10% fish meat extract added various amounts of glucose showed the best growth on the FME agar containing 1% glucose. Among several media tested a medium which consists of 1% glucose, 0.25% yeast extract and 1.5% agar was the best for the growth of MG-fungus. This medium was named as GY-medium. The fungus grew better on the GY-medium than on the FME agar, though it grew somewhat better on a modified FME agar containing 1% glucose than on the GY-medium. The fungus was capable of growing on an agar containing 0.25% yeast extract only, but incapable on an agar with 1% glucose only. This showed that a growth factor of the fungus existed in yeast extract. The fungus grows on neither Sabouraud dextrose agar nor Czapex dox agar. Culturing tests using the FME agar added in various concentrations the main ingredients of Sabouraud dextrose agar and those of Czapex dox agar revealed that a combination of 4% glucose and 1% peptone and that of 3% glucose and 0.1% K2HPO4 inhibit the growth of the fungus.
Three species of the genus Glugea (Microsporidea : Nosematidae), G. plecoglossi TAKAHASHI et EGUSA, 1977, G. anomala (MONIEZ, 1887) GURLEY, 1893 and G. hertwigi canadensis FANTHAM et al., 1941, were studied on their spore surface construction and dimentions with a scanning electron microscope. Spores of G. plecoglossi were collected from both fresh and the formalin-preserved Plecoglossus altivelis. Fresh spores of G. anomala from Gasterosteus aculeatus were sent by Dr. J. LOM of the Czechoslovak Academy of Sciences and spores of G. hertwigi canadensis were gathered from a frozen Canadian smelt, Osmerus mordax, imported commercially from Canada. These spores were fixed in 2% glutaraldehyde in 0.1 M phosphate buffer of pH 7.4 for 90 minutes and then in 2% osmium tetraoxide in the same buffer for 60 minutes. After fixation, they were rinsed, dehydrated by passage through a graded series of ethanol, replaced with isoamyl acetate, dried with a critical point dryer, coated with golden ion and examined with the Hitachi MSM-6 at accelrating voltages of 25kV. G. plecoglossi spores have the smooth surface, though an exception with a fine wrinkle-like structure was found in the formalin-preserved specimens. The treated fresh spores of G. plecoglossi measured 3.9-5.1μm long by 1.7-2.1μm wide, being a little smaller than the figures of 5.1-6.2μm long by 2.0-2.5μm wide reported on the basis of optical microscopic observations. The formalin-fixed spores did not shrink through the treatment. Glugea sp. AWAKURA, 1974 from P. altivelis is distinctly different from G. plecoglossi, because, first, the formalin-preserved spores are bigger than those of G. plecoglossi, being 5.9-6.9 μm long by 2.0-2.4 μm wide according to an optical microscopic observation, and secondly, they have dense fine folds on the surface. G. anomala spores were characterized by the highly rugose surface with a winding longitudinal ridge. G. hertwigi canadensis spores had the rough surface with loose folds and distinct or obscure longitudinal wrinkles which was slightly different from that of G. hertwigi reported by LOM and WEISER in 1972.
Vibrio anguillarum is well known as the causative agent of vibriosis in ayu (Plecoglossus altivelis) in Japan. During the diagnostic works on the vibriosis in cultured ayu in Tokushima Prefecture from 1976 to 1977, many strains were obtained. Among them, 52 strains were submitted to characterization tests, and these strains were found to be identified as Vibrio anguillarum. The problem is, however, that 27 strains out of 52 strains were not sensitive to the vibriostatic agent 0/129 (VSA). In ayu culture, many therapeutic agents such as chloramphenicol, oxolinic acid, and nalidixic acid have been used, and recently, trimethoprim mixed with sulfadoxine (TS) has been used. Among those drugs, the new one, TS, was suspected of producing VSA-nonsensitive strains. Then, the relationship between the sensitivity of the isolates to VSA and that to TS was examined. As a result, minimal inhibitory concentration of TS for the four VSA-sensitive strains and the four VSA-nonsensitive strains were found to be 1.2μg/ml and 24.0μg/ml, respectively. Furthermore, it was confirmed that the VSA-sensitive strains lost their sensitivity to VSA when they became resistant to TS by passing through TS containing media. In consequence, it was concluded that some strains of V. anguillarum lost their sensitivity to VSA by obtaining resistance to TS administered to diseased ayu in ponds.
From the begining to the end of July in 1977, a numerous number of akame (Liza akame) with skin ulcer had been observed in the estuary of the River Ashida in Fukuyama City. Results of parasitological and bacteriological investigations made on 36 samples are summarized as follows. 1) A parasitic copepod, Caligus orientalis, was observed on the skin of all the specimens with one exception. The mean number of the worm per fish was about 27. 2) Various kinds of bacteria were isolated from the skin lesion. These were classified as Moraxella spp., Klebsiella sp., Citrobacter sp., Proteus vulgaris, Edwardsiella tarda, Vibrio spp., and Pseudomonas sp. 3) It was assumed that C. orientalis inflicted wounds on the body surface where the bacteria gained a foothold of invasion.