The effect of the addition of the aminoglycoside antibiotic tobramycin to the culture medium on selective isolation of Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease, from ayu Plecoglossus altivelis was examined. The minimum inhibitory concentrations of tobramycin against all 37 strains ofF.psychrophilum tested were more than 6.3μg/mL. The addition of tobramycin to medium at a concentration of 5μg/mL was a better method for the isolation of F.psychrophilum, because the overgrowth of other bacteria was inhibited and the isolation rates of F.psychrophilum were improved. Especially, the use of tobramycin-supplemented medium could be effective in the examination of the external organs of carrier fish, in which viable bacterial counts of F.psychrophilum are lower than those of other bacteria.
Post-mortem myoliquefaction caused by myxozoans of the genus Kudoa was observed in Japanese flounder Paralichthys olivaceus and Chinese sea bass Lateolabrax sp. cultured in Japan. Morphological and molecular analyses of the myxozoan from Japanese flounder identified it as Kudoa thyrsites, which has been described from various marine fishes in different oceans. The parasite from Chinese sea bass was similar to K. thyrsites, having stellate spores with one polar capsule larger than the other three. However, the spore size was smaller than that of K. thyrsites. The small subunit rDNA sequence from the Kudoa sp. of Chinese sea bass was distinct from that of K. thyrsites and phylogenetic analysis placed it as an outlier to K. thyrsites. Therefore, we describe the myxozoan from Chinese sea bass as Kudoa lateolabracis n.sp.
We determined the nucleotide sequence of a 8.6 kb DNA region containing etfA encoding a putative fimbrial major subunit from chromosomal DNA of Edwardsiella tarda KG8401 which expresses mannose-resistant hemagglutination (MRHA). This region contained three novel genes, etfBCD, at the downstream region of etfA . The deduced amino acid sequences of EtfABCD contained conserved fimbrial domains; fimbrial protein, fimbrial chaperone, fimbrial usher and fimbrial protein, respectively. Escherichia coli transformed with the cloned etf operon expressed MRHA and fimbriae that reacted with rabbit antiserum against the fimbrial major subunit of E. tarda, showing the implication of the fimbriae in the hemagglutination of E. tarda.
Infectious hematopoietic necrosis (IHN) is an acute, systemic, rhabdoviral disease of salmonid species. To date, the effective approach in preventing or treating this epizootic disease is unknown. In this study, a genetic cross was established to elucidate the genetic markers associated with IHN resistance in rainbow trout Oncorhynchus mykiss. An IHN-resistant paternal strain of was crossed to a susceptible maternal strain to produce a F1generation. Mating F1males back to the maternal strain created F2, a backcross generation. Five backcross families were generated and IHNV was challenged on 92 individuals of each family. Linkage analysis was performed on the backcross families using 96 microsatellite markers from 25 linkage groups. LOD score as well as p values using the Pearson goodness of χ2-test were calculated to identify the chromosomal regions associated with IHN resistance. The highest LOD score of 0.952 (θ=0.39) was obtained in one backcross family. A novel chromosomal region (p = 0.011) on linkage group 2 consists of a cluster of 4 microsatellite markers, OmyFGT3TUF, OmyFGT25TUF, OmyRGT35TUF and BFRO0001, and they were identified as a potential region for quantitative trait loci of IHN resistance in rainbow trout.
Two Japanese isolates of viral hemorrhagic septicemia virus (VHSV), JF00Ehi1 (Genogroup I) and KRRV-9601 (Genogroup III), from Japanese flounder Paralichthys olivaceus were examined for the virulence to rainbow trout Oncorhynchus mykiss and 4 species of marine fish. Rainbow trout injected intraperitoneally with each isolate at a dose of 107.5 TCID50/fish showed neither death nor hemorrhage in the skeletal muscle, while the mortalities in Japanese flounder were both 100%. The mortalities by intramuscular injection with JF00Ehi1 at a dose of 107.0 TCID50/fish were 95.0%, 75.0% and 97.5% in black rockfish Sebastes inermis, red sea bream Pagrus major and yellowtail Seriola quinqueradiata, respectively.
Effects of different salinities (8, 17, 24, 27, 30 and 34 ppt) on the egg laying, egg hatching and oncomiracidial swimming behavior of the monogenean Neobenedenia girellae were examined in vitro . Egg laying ability was affected at 8, 17, 24 ppt salinity and the number of laid eggs at these salinities were significantly lower than at 34 ppt salinity (control). Egg hatching rates at 8 and 17 ppt salinity were significantly lower than that of the control. The rate of non-motile oncomiracidia at 8 and 17 ppt salinity was significantly higher than that of the control. The results suggest that culturing fish in seawater with low salinity could be effective to control N. girellae infections in aquaculture.
Mass mortality occurred in 2-year-old koi (fancy carp) Cyprinus carpio in Taiwan in 2002. Affected fish did not show any external signs except swollen gills. The consistent histological changes were observed in the gills;hyperplasia of epithelial cells, infiltration of eosinophilic granular cells and fusion of the secondary lamellae. Negatively stained nucleocapsids were icosahedral and 112±1nm in diameter. Koi herpesvirus (KHV) was detected in the diseased fish by PCR using specific primers for KHV, and sequence of the amplicon showed a 99% identity with the published data. This is the first report of KHV infection in Taiwan.
It is necessary to determine the quality control ranges of the minimum inhibitory concentrations (MICs) for fish pathogenic bacterial strains in order to achieve comparability of test results. We derived tentative quality control ranges for Lactococcus garvieae and Photobacterium damselae subsp. piscicida (2 strains each), by using the standard agar dilution method of the National Committee for Clinical Laboratory Standards. We measured the MICs of 14 drugs for the 4 strains and 5 quality control strains under culture conditions recommended for both aquatic bacteria and determined tentative quality control ranges from the modal MIC±1 log2 dilution step.
The Pharmaceutical Administration and Regulations Law has been revised in Japan during 2003, resulting in a big confusion on fish disease control practice, because limited fish drugs and vaccines have been allowed to use in only a few fishes. This context motivated the Japanese Society of Fish Pathology to organize a symposium (4th/April/2004) at Kagoshima. The symposium was focused on the up-to-date disease control methods with respect to food safety, drug administration with scientific evidences, extension of available fish species in drug and vaccine administrations, responses of fish farming associations and pharmaceutical companies to the revised law. Finally, it was reconfirmed that the drug and vaccine administrations under the tight law and HACCP operations give the safety of farmed fish products to consumers.