Susceptibilities of jack mackerel to Streptococcus sp. and Pasteurella piscicida of yellowtail origin were studied in experimentally induced infections, comparing with those of yellowtail. In intraperitoneal injections of Streptococcus, mortalities and epicarditis-development rate in jack mackerel were as high as those of yellowtails. Intraperitoneal injections of Pasteurella also induced high mortalities with histopathological features in jack mackerel as well as yellowtail, but the pathogenicity for jack mackerel was less than that for yellowtail. In both the bacterial challenges by peroral and immersion methods, jack mackerel did not show any specific symptom and clearly differed from yellowtail which showed comparatively high mortalities with development of naturally occurring-like lesions in their viscera. The present results suggest that jack mackerel is a useful laboratory animal in the screening test of chemotherapeutic agents for controling diseases of yellowtail.
The survival of three salmonid viruses; infectious hematopoietic necrosis virus (IHNV), infectious pancreatic necrosis virus (IPNV) and Oncorhynchus masou virus (OMV), in fish rearing water, dechlorinated city water, double-distilled water, and Hanks' BSS were observed at 0, 5, 10 and 15°C. In addition, interaction between viruses and microorganisms present in the rearing water was observed. The results obtained are summarized as follows: 1. IPNV was stable in all kinds of waters employed at every temperature tested for 14 days, but it was observed that, for IHNV, as the temperature increased, the loss of infectivity also increased. 2. OMV was labile even in Hanks' BSS and inactivated rapidly as the temperature was raised. Infectivity declined to less than minimum observable amount at 14 days postincubation both at 10 and 15°C. It was not survived at 5 to 7 days later in the fish rearing water. 3. When IHNV or OMV was suspended in filtered rearing water, titer reduction of the viruses was suppressed in comparison with the untreated water. This phenomenon was more conspicuous in the autoclaved water. 4. The infectivity of IHNV declined to less than minimum observable amounts at 3 days after incubation at both 5 and 15°C, when it was suspended in filtrated culture to which rearing water was added with 10% MEM 10 and incubated at 15°C for 2 days. In microflora of the culture, Achromobacter and Pseudomonas were dominant and the ratio was 7:3. 5. Representative strains of Pseudomonas has been proven to have the ability to produce anti-IHNV substance.
A myxosporean found in the brains of Lateolabrax japonicus, Seriola quinqueradiata, Pagrus major and Takifugu rubripes was characterized by producing two forms of spores; hexaradiate spores with six shell valves and six polar capsules and heptaradiate spores with seven shell valves and seven polar capsules. The description of these forms was given. These two forms of spores coexisted in intracerebral pseudocysts and extracerebral cysts in all the fish studied. The ratio between the two was variable. The generally accepted principle that the number of shell valves is constant in a given species of the order Multivalvulida and therefore serves as the main family criterion does not apply to this myxosporean. From the observations it may be assumed that one of the two forms is abnormal due to an unusual cell division, or this myxosporean is on an extention of the Trilospora-Kudoa-Pentacapsula-Hexacapsula evolutinary line, but its character is still genetically unfixed. Further research on these questions is needed to discuss the systematic position of this myxosporean.
The occurrences of Vibrio ordalii(V. anguillarum biovar II)infection in ayu(Plecoglossus altivelis)and fingerlings of rockfish(Sebastes schlegeli)are reported. The former fish was reared in freshwater ponds and the latter in net cages in the sea. These are the first records of V. ordalii infection in non-salmonid fishes. The V. ordalii isolates were confirmed to share both heat-labile and heat-stable common antigens with J-O-1(A)serotype of V. anguillarum.
Toxins produced by Aeromonas hydrophila strain A10 in the muscle of carp at the site of injection were studied. Carps injected with the crude toxins showed swelling and reddening of the body surface as those injected with the live bacteria. The toxic substance was partially purified from a extract of the necrotized muscles by ammonium sulfate precipitation, ion-exchange chromatography and gel filtration. As a result, it was suggested that α-type hemolysin was implicated in the toxicity.The hemolysin was heat-labile, and inactivated by EDTA, trypsin and papain, but stable at pH value between 4.0 and 11.2.
The morphological, biochemical and physiological characteristics of 23 strains of gliding bacteria isolated from diseased cultured flounder, Paralichthys olivaceous, in Japan were determined. The strains were classified into two groups: Group I (83%) was identified as Flexibacter maritimus and Group II(17%) was tentatively identified as Flexibactersp. until further characteristics will be studied to confirm its taxonomic identity.