A birnavirus, CV-TS-1 strain isolated from cultured hard clam (Meretrix lusoria) was inoculated to the hard clam by means of intrapalleal cavity injection or water borne method at 25°C. Cumulative mortalities of clams injected with the virus at the concentrations of 104.7, 103.7 and 102.7 TCID50/clam were 37.5%, 32.5% and 25%, and those of clams immersed to virus solutions of 106.0, 105.0and 104.0TCID50/mlwere 30%, 25% and 15%, respectively. Temperature stress (increase from 25°Cto 33°C or decrease from 25°C to 15°C) was given to clams before and after virus challenge by exposure to a virus solution of 105.0 TCID50/ml. Mortality increased markedly when temperature was increased after virus infection, though either the decrease in temperature after virus challenge or increase or decrease in temperature before the challenge did not affect the mortality.
A preventive trial of viral nervous necrosis (VNN) in larval striped jack Pseudocaraux dentex was made by selecting virus-free spawners based on the detection of the causative virus (SJNNV) gene by polymerase chain reaction (PCR) method. PCR detection of SJNNV gene from fish was done by amplifying the target sequence (T4 : 426 bp) of the coat protein gene (RNA2). Four spawner groups, each consisting of 12 to 16 fish, were examined for the presence of SJNNV in their gonads just before spawning at one month intervals. Their offsprings (eggs and larvae) were subjected to rearing experiments to observe the occurrence of VNN. The SJNNV gene was detected from some spawners of these groups at the late spawnings. VNN occurred in larvae from spawner groups including SJNNV gene-positive fish, but not in larvae obtained from spawner groups which consisted of SJNNV gene-negative fish. These results suggest that the selection of striped jack spawners based on the detection of SJNNV gene from gonads by PCR just before spawning is efficacious for the prevention of vertical transmission of SJNNV in seed production.
The birnaviruses, viral deformity virus (VDV) and yellowtail ascites virus (YAV) isolated from cultured yellowtail, Seriola quinqueradiata, were examined for their serological and biochemical properties. Cross-neutralization studies showed that VDV was closely related to YAV but clearly distinct from the 3 type strains of infectious pancreatic necrosis virus (IPNV). VDV and YAV contained two genome segments and mobility of the smaller segment showed a slight difference between the two. On the other hand, polypeptide electropherotypes showed a clear difference between VDV and YAV.
In vitro antibacterial activity of fosfomycin (FOM), a cell-wall synthesis inhibitor, was investigated against Pasteurella piscicida, the causative agent of pseudotuberculosis in yellowtail Seriola quinqueradiata. Minimum inhibitory concentrations (MIC) of FOM against 68 isolates of P. piscicida, including strains resistant to other antibiotics, ranged from 1.56 to 3.13 μg/ml. Bactericidal activity of FOM was evident at the MIC level. Therapeutic effect of FOM was studied in yellowtail experimentally infected with P. piscicida. The cumulative mortalities among infected fish after oral administration of FOM at doses of 0, 5, 10, 10, 30 and 40 mg/kg/day for 5 consecutive days from 1 h after infection were 60, 45, 45, 15, 5 and 0%, respectively. Based on the results obtained in this study, FOM may be a new therapeutic agent against pseudotuberculosis in yellowtail.
A disease occurred among 0 and 1-year-old shotted halibut, Eopsetta grigorjewi which were hatcheryreared and cultured for releasing, and 3, 4 and 5-year-old shotted halibut which were cultured as brood stocks. External signs were redness of the head and the body surface, and erosion of the lip. Bacteria were isolated from the kidney, spleen or brain of the diseased fish. The isolates were identified as atypical Aeromonas salmonicida by the biochemical and serological properties. Intramuscular injection of an isolate into Japanese flounder, Paralichthys olivaceus produced signs similar to those of the spontaneously diseased shotted halibut and caused death.
Characteristics of natural killer-like cells (NK-like cells) in carp (Cyprinus carpio) were studied by 51Cr-release assay. Among cells examined, K562 cells (human erythroleukemic cells) were found to be the most suitable as target cells for NK assay in carp. Pre-incubation of the leucocytes from head kidney and peripheral blood enhanced NK activity. Leucocytes from the head kidney and kidney showed the highest NK activity and those from peripheral blood, thymus and spleen followed in the order. The cold target inhibition test indicated that carp NK-like cells consist of more than one population for target recognition.
Optimal conditions for the isolation of salmonid herpesvirus type 2 (SH-2) from the diseased maricultured coho salmon, Oncorhynchus kisutch, were studied.CHSE-214 cells had the highest susceptibility to SH-2 among the cell lines tested (CHSE-214, RTG-2, SSE-5, BB, EPC and FHM). Optimal temperature for the virus culture was 10-15°C and freezing of the sample organ markedly decreased the virus titer.Homogenates of both the liver and the heart showed high virus titers.Conclusively, for the isolation of SH-2 from maricultured coho salmon it is recommended to use the pooled sample of the heart and the liver without freezing, inoculate the sample homogenate on CHSE-214 cells, and incubate at 10-15°C.