A histopathological study was made on Pseudomonas fluorescens infection which occurred in the spring of 1979 in pond-cultured tilapia, Sarotherodon niloticus. The infected fish showed exophthalmia, dark body coloration, spotty or nodular lesions in the liver, spleen, kidney and gills, and inflamed swim-bladder. The bacterial dissemination was systemic. The histopathological aspects were abscess formation in eyes, spleen and swim-bladder, and focal necrosis in the liver, gills and kidney of some diseased fish. The other fish showed granuloma formation in all infected lesions.
A histopathological study was made on an infection of Streptococcus sp. in cultured tilapia, Sarotherodon niloticus, which occurred in warm water ponds during the winter of 1980. The external signs were dermal hemorrhage and exophthalmia. The internal signs were dropsy, epicarditis, peritonitis, pale-colored liver, splenomegary and nodule formation in gonads. On histopathological examination, the bacterial dissemination was systemic. Abscesses and granulomas were found to develope in the infected orbital adipose tissue of the exophthalmic eyes. Infiltration of bacteria-laden macrophages and granuloma formation were observed in the infected lesions of the epicardium, capsules of the liver and spleen, peritoneum, stomach, intestine, brain, ovary and testis.
Vertebral deformity occurred in cultured marine fish, yellowtail (Seriola quinqueradiata) at an occurrence rate of 2.1% from July to September, 1982 in Mie Prefecture. Eighteen deformed fish (11-15 cm in body length) were investigated with bacteriological, soft radiographical and histopathological technics. β-hemolytic streptococcal bacterium was dominantly isolated from the brain of the diseased fish and identified as Streptococcus iniae. The soft radiographical technic confirmed that the deformity was due to vertebral lordosis, kyphosis and scoliosis at the trunk and tail parts. The histopathology of diseased fish was characterized by a massive infiltration of cocci-laden macrophages and production of granulomas containing cocci in the third ventricle, maninges and granular layer of cerebellar cortex of the brain. There were also granulomas in the hepatec capsule and peritoneum.
Excellent protection against vibriosis was provided to ayu, Plecoglossus altivelis, vaccinated by the immersion method with either formalin-killed bacterin, sonicated bacterin, or lyophilized formalin-killed bacterin of Vibrio anguillarum. Lipopolysaccharides of V. anguillarum also induced protective immunity against vibriosis in fish vaccinated by the immersion method. No agglutinating antibodies were detectable in the serum of fish vaccinated by immersion with vibrio bacterin; however, antibodies were detected in the serum of fish vaccinated by intraperitoneal injection of formalin-killed bacterin mixed with Freund's complete adjuvant. There were no differences in the profiles of protein components of the serum of immersion vaccinated fish and non-vaccinated fish. No differences were recognized in the protective immunity against vibriosis between fish which received the serum from immersion vaccinated fish and those which received the serum from non-vaccinated fish.
To clarify the protective properties of Edwardsiella tarda lipopolysaccharide (LPS) reported previously, immunogenicity, antigenicity and chemical characteristics were examined using crude LPS, pure LPS, polysaccharide and lipid A prepared from one strain of E. tarda. The eels immunized by intramuscular injection with the four preparations showed an increase in agglutination titer in comparison to control group. The highest titers were recorded in eels immunized with crude LPS preparation and the lowest with the lipid A preparation. However, titer did not correlate with the survival rate after challenge. The highest survival was demonstrated in the eels immunized with the polysaccharide preparation and some resistance was shown in the eels immunized with the crude LPS preparation. The eels immunized with pure LPS and lipid A preparations did not show protection to challenge. Using Ouchterlony immunodiffusion, it was shown that the antigenicity of the polysaccharides were lower than pure LPS where no precipitin lines were observed. Chemical analysis showed a high degree of heterogeneity in the crude LPS with a small amount of protein and high content of nucleic acids. After further purification, protein and nucleic acids were reduced, but present. From these results it was concluded that the main protective substance in the E. tarda crude LPS preparation was polysaccharide.
Range and optimum of growth temperature for Aeromonas hydrophila, Edwardsiella tarda, Pseudomonas anguilliseptica, Vibrio anguillarum, and V. vulnificus were determined by testing 10 or 15 strains of each species with a temperature-gradient shaking incubator. Aeromonas hydrophila, E.. tarda and V. vulnificus biogroup 1 grew optimally at temperatures between 30 and 35°C. Vibrio anguillarum and V. vulnificus biogroup 2 grew optimally at 25-30°C and P. anguilliseptica at 22-27°C. The differences in growth temperature among intra-species subgroups separated by serotype, virulence or biotype were also studied.
From the end of August to late in October 1983, an epizootic occurred among 60 colored carp Cyprinus carpio in a garden pond of a businessman in Mihara city, Hiroshima Prefecture. Affected fish exhibited hemorrhage and erythema on the body surface and fins. From the kidney, spleen and liver of moribund fish, Edwardsiella tarda was purely isolated, and the isolates were confirmed to cause mortality not only in carp but also in Japanese eel Anguilla japonica. This is the first recorded case of edwardsiellosis in carp.
Changes in intestinal flora of the juvenile eel, Anguilla japonica, after beginning to feed were studied. The juvenile eel just after being caught had no detectable bacteria in the intestines, but after beginning to feed, they always had 106-107 colony forming units of bacteria per gram of intestine with contents. When they were fed Tubifex sp. as an initial food, the composition of intestinal flora of the eel was as follows: Streptococcus, 33 %; Enterobacteriaceae, 43%; Aeromonas, 1 %; Plesiomonas, 15%; Acinetobacter, 1 %; Achromobacter, 4%; others, 2 %. This composition was similar to that of bacterial flora of Tubifex sp., that is, the bacteria in the intestines seemed to be simply transferred from Tubifex sp. to the eel. When the food for the eel was changed to the mixture of Tubifex sp. and formula food, the intestinal flora of the eel consisted of Streptococcus (13 %), Enterobacteriaceae (50%), Aeromonas (9 %), Plesiomonas (11 %), Acinetobacter (6 %), Achromobacter (7 %) and others (4 %). When the food was completely changed to formula food, the following was the intestinal flora: Streptococcus, 25%; Enterobacteriaceae, 12 %; Aeromonas, 16%; Acinetobacter, 17 %; Achromobacter, 4 %; others, 15 %. As a result, the composition of the intestinal flora of the eel had a tendency that the percentage of Enterobacteriaceae decreased, and those of Aeromonas and Acinetobacter increased, with the change of food from Tubifex sp. to formula food.