To investigate the defence mechanisms of the eel Anguilla japonica against Edwardsiella tarda, the chemotactic, phagocytic and bactericidal activities of phagocytes isolated from the posterior kidney of immunized and control eels were examined in the absence of serum. Additionally, the opsonic activity of both immune and control serum was investigated. Agglutination titers to E.tarda significantly increased 1 to 3 weeks after immunization. In the absence of serum, the chemotactic activity of phagocytes from immunized eels increased 3 weeks after immunization. Phagocytic activity was highest 3 weeks after immunization. Opsonic activity was detected in immune serum. The addition of immune serum increased phagocytic activity, but this increase was reduced by heating of the serum. Bactericidal activity of phagocytes, in the absence of serum, was not enhanced by immunization. It is concluded that immunization of eel enhances the chemotactic and phagocytic activity of phagocytes.
A skin ulcer disease frequently occurred in yearling Japanese flounder, Paralichthys olivaceus, cultured in artificial propagation facilities along the coasts of Hokkaido, Japan. The present study confirmed that the disease was induced by the ectoparasitic flagellate, Ichthyobodo sp., which attached to the skin and gills. The external sign was restricted to the dorsal skin, and was characterized initially by increased secretion of mucus. It then developed to extensive epidermal erosion and ulcer with increasing number of parasites. The heavy infection caused hyperplasia of the malphigian cells and depletion of mucous cells, and led to epidermal spongiosis due to the intercellular edema. The destruction of epidermal tissues was followed by remarkable changes of the dermis in the strutum spongiosum such as the infiltration of lymphocytes and expansion of scale pockets, suggesting that loss of osmotic balance caused by the integumental breakdown may be the major cause of mortality of the infected fish.
Optimum methods for evaluating virucidal activities of germicides to infectious pancreatic necrosis virus (IPNV) and infectious hematopoietic necrosis virus (IHNV) were studied. 1. Among the fish cell lines examined CHSE-214 and EPC cells were best suited for examining virucidal activities. 2. Cell-associated virus suspension (CAV) was effectively obtained by freezing and thawing cell-sheet culture just before the appearance of cytopathological effects (CPE). 3. CAV of IPNV did not change in infectivity titer during the stocking period of 8 weeks at either -20°C or -80°C. However, infectivity titer of IHNV in CAV significantly decreased infectivity titer at both -20°C and -80°C. 4. Virucidal activities of IPNV and IHNV did not change during 6 h incubation at temperatures from 10°C to 37°C and from 10°C to 15°C, respectively. Hence, 15°C appears to be a reasonable temperature for routine use in this assay system. 5. Toxicities to IPNV and IHNV of germicides other than halogenic compounds were successfully eliminated by 102-105 dilutions of PBS (-).
The virucidal activities of ethanol, methanol, propanol, phenol, cresol, iodophor and chlorine were examined. Infectious pancreatic necrosis virus (IPNV) was inactivated by ethanol, methanol, cresol, iodophor and chlorine but was not inactivated by propanol or phenol. Inactivation of IPNV required long-term exposure to a high concentration of cresol. Iodine and chlorine effectively inactivated IPNV suspended in PBS (-). The virucidal activities of ethanol, cresol, iodophor or chlorine were eliminated in the presence of organic substances.
A new myxosporean, Myxobolus episquamalis sp. nov. is described from the scales of the mullet, Mugil cephalus in Japan. Lerge, flat cysts developed on the surface of the apical area of the scales were formed of polysporous trophozoites which varied greatly in shape, being mostly irregularly winding, branched hypha-like bodies. Spores were oval in front view, tapering anteriorly to a blunt apex and lenticular in lateral view. Most spores were completely covered with a thick mucus envelope. Pyriform polar capsules were somewhat unequal in size and without visible filament coils. The sporoplasm contained an iodiophilous vacuole. Each valve had a nipple-shaped thickening with an opening of the polar capsule on the sutural edge at the apex and irregularly folded on the margin. Dimensions (μm) of fresh spores : length, 7.5-9.5 (8.6); width, 6.0-7.5 (6.8); thickness, 4.5-5.5 (5.1); polar capsules : length, 3.8-5.0 (4.4); width, 2.0-3.0 (2.2).
The immunomodulatory effects of levamisole were investigated using rainbow trout, Oncorhynchus mykiss. Fish sampled 5 days after intraperitoneal injection of levamisole showed increased protection against Vibrio anguillarum when a single dose (0.5 mg/kg) was used. Phagocytic activity, chemiluminescence responses and natural killer cell activity in fish treated with levamisole were also increased, compared with those in the saline treated fish. Furthermore, levamisole activated the alternative complement pathway of rainbow trout, although serum bactericidal activities against V. anguillarum were not enhanced by the treatment of levamisole. These results indicate that levamisole has immunomodulatory effects in rainbow trout.
A field survey was carried out for four years in order to investigate the occurrence of Flavobacterium branchiophila infection at the Okutama Trout Hatchery affiliated to Tokyo Metropolitan Fisheries Experimental Station. The gills and the skin of fish collected from rearing ponds were examined by indirect fluorescent antibody technique (IFAT), plating method and light microscopy. The water from the fish ponds was also examined. IFAT were more sentitive and specific in detection of F.branchiophila than plating method or light microscopy. F. branchiophila was always associated with bacterial gill disease outbreaks that exhibited typical clinical signs. In other words it was detected from both fish and water during the period of the outbreaks only. Outbreaks of F. branchiophila gill disease occurred intermittently in the same fish population. Therefore the recovered fish appeared not to obtain immunity against the pathogen.
A rickettsiales-like organism was isolated in cell culture from coho salmon (Oncorhynchus kisutch) reared in seawater net pens in the vicinity of Puerto Montt, Chile S. A. and experiencing an epizootic with accompanying mortality. The organism, observed in fish and isolated in cell culture, was GRAM-negative, pleomorphic, predominantly coccoid in shape, and approximately 1μm in diameter. It replicated, producing cytopathic effect (CPE) in cell lines from four species of salmonids, but failed to grow in any of eleven standard bacteriological media. The optimal temperature for replication was 15-18°C based on the production of CPE. Streptomycin, gentamicin, and tetracycline were inhibitory for the organism, but it was not sensitive to penicillin. The isolated organism stained with GIEMSA and PINKERTON'S stains and with a modified GIMENEZ stain. It did not react with a monoclonal antibody against the group-specific LPS chlamydial antigen. On the basis of available information, we suggest this organism is a member of the order Rickettsiales and represents the first isolation of a member of this group from an aquatic poikilotherm.