Virological examination was carried out on the kidney and spleen of anadromous amago caught by the floating gill net in Nagara River and Miyagawa River in May, 1981. Tissue extracts were inoculated onto CHSE-214(chinook salmon embryo)cells. Virus which exhibited cytopathic effect in CHSE-214 cells were isolated from 9 of 71 fish from Nagara River and 1 of 4 fish from Miyagawa River. The isolates both from Nagara River and Miyagawa River were neutralized by anti-IPNV(Gifu)rabbit serum, indicated that they were antigenically related to IPN virus. Among 71 sera of fish from Nagara River, 20 specimens showed the neutralization titer over 1:8 against IPNV. The source of virus was discussed in relation to the released stock cultured in pond.
Susceptibilities of 7 fish cell lines, RTG-2, CHSE-214, FHM, EPC, CSF-1, EK-1 and EO-2 cells, to 5 eel viruses, EV-I(EVE), EV-II, EV-III(EVEX), EV-IV and EV-V were studied. The viruses were subcultured for 3-5 times on monolayer cell sheets in microplates at 20°C and susceptibilities were determined by the replication titers calculated by TCID50 analysis. Among the fish cell lines both EK-1 and EO-2 cells derived from Japanese eel exhibited the highest susceptibility to all the eel viruses except EV-II. RTG-2 and CHSE-214 cells showed next higher susceptibility to them. On the other hand, FHM, EPC and CSF-1 cells showed low susceptibility to all these eel viruses. Titers of EK-1 and EO-2 cells to the eel viruses were observed to be more constant than those of RTG-2 and CHSE-214 cells during subcultures. Above mentioned results indicate the advantage of using eel cell lines for the study of eel viruses.
Three marine cercariae, Cercaria pectinata, Cercaria tapidis and Cercaria sp. were found in the short-necked clam Tapes philippinarum from Lake Hamana, Japan. These cercariae are the first reported marine cercariae from the area. Of 3, 200 clams examined, 110 infections for C.pectinata, three for C.tapidis and one for Cercaria sp. occurred. C.pectinata is a yellowish, non-oculate, trichocercous, fellodistomid cercaria, developing in large saccular sporocyst in the host gonad. C.tapidis is an oculate cercaria with long tail of five times as body, and Cercaria sp. is a non-oculate, furcocercous, gymnophallid cercaria, and both species develop in sporocyst. The infection rate by C.pectinata showed a seasonal change, being low(0-1.2%)from May to August and relatively high (2.0-3.6%)from September to March. Histologically, sporocysts in early stage were found in inter-follicular spaces, and were observed to grow in size in situ with the duration of time and to occupy finally the greater part of the gonad;ripe sporocysts with numerous mature cercariae were observed from March to April.
In 1981, red spot disease occurred in European eels (Anguilla anguilla) in Scotland, and this seems to be the first record of the disease in Europe. Then two strains isolated by Dr. D. J. STEWART in Scotland were compared with Japanese representative strains of Pseudomonas anguilliseptica. According to the results of biochemical characterization tests, agglutinin reactions, precipitin reactions, and pathogenicity tests for Japanese eels (A. japonica) and European eels, the Scottish strains proved identical to strain no. 2, the representative strain of K antigen-lacking type (K-type) of P. anguilliseptica.