Aerobic bacteria in the intestines of pond-cultured eels fed with raw fish were studied, with special reference to their gross quantitative changes with the progress of fasting, seasonal variations, and the appearance of fish pathogenic bacteria. In apparently healthy eels aerobic bacteria in the intestines reduced markedly in number with the progress of fasting and the intestines became “nearly” sterile after 3 week fasting in almost all fishes. Most of isolates were members of the genera Pseuomonas, Vibrio, Flavobacterium, Aeromonas, Achoromobacter and Alcaligenes. The occurrence of each genus changed with the season and pond, and no regular intestinal inhabitant was found. Part (9%) of isolates were demonstrated by experiment to be pathogenic to fish and all the fish pathogenic bacteria were members of the genus Aeromonas.
For the past several years “bacterial tuberculoioidosis” has caused severe losses among young fishes of Seriola quinqueradiata and S. purpurascens cultured in various parts of Japan. The name “bacterial tuberculoidosis” was proposed by KUBOTA et al (1970) on th basis of the symptomatology and histopathology of the disease, though the causative agent responsible for it was not isolated. The present authors succeeded repeatedly in isolating the causative bacterium in pure culture from lesions of spleen and kidney of affected fish which were obtained on the occasions of outbreaks of the disease in Miyazaki, Oita and Ehime Prefectures during the period from 1969 to 1970. The bacterium when inolulated into Seriola caused the same pathological features as seen in naturally affected fish and killed them. The bacterium grew well on Brain heart infusion agar containing fresh human or rabbit blood and Brain heart infusion broth containing rabbit serum, both with 3% NaCl, but very poorly on ordinary nutrient agar or broth with 3% NaCl. In 2-day old cultures, grown on blood agar, cells were straight or slightly curved rods of 0.6 by 1.6 microns in the average size and arranged singly, in pairs or in chains. They were Gram-positive in young cultures but changed into Gram-negative after about 18 hours generally. Cells exhibited pleomorphism and had metachromatic granulus at the both ends of the cells. They did not form spores and were non-motile in semisolid agar madia. Capsules were absent. The bacerium was a facultative anaerobe. Nitrates were not reduced and neither indole (Kovac's method) nor hydrogen sulfide was produced. The oxydase test, methyl red test and catalass test were all positive, and the Voges-Proskauer test was negative. Gelatin was not liquefied. Agar Plates containing rabbit erythrocytes showed alpha-hemolysis. Acid was produced from glucose, mannose, levurose and galactose, but other sugars tested were not fermented. The bacterium was definitely sensitive to penicillin. On the basis of these observations, it is assumed that this organism is more closely related to the genus Corynebacterium than to any other known genera.
The toxicity, therapeutic effect and distribution of 1-(5-nitro-2-furyl)-2-(6-amino-3-pyridazyl)-ethylene hydrochloride(nifurprazine hydrochloride, HB-115 HCl)were investigated in ayu, a salmonoid fish. The results were as follows. 1. Ayu frys were immersed in the water containing various concentrations of HB-115 HCl at various temperatures(11-26°C)for 6 hrs., and then transferred into clean water.Mortalities were checked 3 days later. Minimum lethal concentrations were 1.6, 4.1, 6.0, 6.0 ppm at 26, 22, 16, 11°C, respectively. 2. When immersing periods were prolonged 1.5 times, toxicities were enhanced apProximately 2 times. 3. Cunative effects of HB-115 HCl on the infection caused by intramuscular injection of Vibrio anguillarum in ayu fish were diminished by increasing the inoculum size. 4. Good therapeutic effects by bathing were achieved by the suitable combination of concentration and immersing period (e. g. 10 ppm-20 mins., 3 ppm-45 mins., 1 ppm-360 mins.). 5. Effects of water temperatures on the therapeutic effects of HB-115 were not noticed. 6. When ayu fishes were immersed in the water containing 2-30 ppm of HB-115 HCl was detected in serum and skin, but not in muscle and viscera.
Biological and biochemical characteristics were studied about the bacteria isolated from lesions of gills, wall of the mouth cavity or body surface of eels (Anguilla japonica), carp (Cyprinus carpio) and rainbow trout (Salmo gardneri) by using Cytophaga agar media by Ordal and Rucker in the summer from 1967 to 1968. The cultures were long flexible Gram negative rods and about 0.5 by 3.7 to 14.8μ. The formation of fruiting bodies and the production of microcysts were observed in 7-day olds cultures on the roach media. The production of microcysts were clearly observed in 2-weeks old cultures in the Cytophaga liquid media. The biological characteristics of 21 strains tested were all the same. Optimum temperature for the growth of the organism in the liquid media was 26.8°C. From the results mentioned above, the organism was identified as Chondrococcus columnaris (DAVIS) ORDAL and RUCKER (1944).