Carp (Cyprinus carpio) hematopoietic cells collected from the kidney were cultured in vitro in 35 mm-diameter tissue culture dishes using 1 mlof RPMI-1640 medium, 20% fetal calf serum, varying concentrations of carp serum and 0.3% agarose. The cells at a concentration of 2 × 105 cells/ml in agar-medium were incubated for 7-10 days at 30°C with 5% CO2. Many small aggregates constituting 3 to 10 cells were observed 3 or 4 days after incubation. Most aggregates grew and formed colonies which were made up of 50 to 100 cells. In contrast, when cultured without carp serum, most of the cells did not multiply and disappeared by day 7. To investigate the colony-forming cell types, agar cultures were dried and stained with May-Grünwald Giemsa. It was found that the colonies containd blast cells, of granulocytes several developmental stages and mature granulocytes. The mature cells had a weakly acidophilic or chromophoric cytoplasm and a single oval or kidney shaped nucleus, and were positive for peroxidase reaction. Electron microscopy showed many granules containing electron-dense materials in the cytoplasm of the matured cells.
Presence of yellowtail ascites virus (YAV) and anti-YAV antibody was examined in the brood stocks of yellowtail Seriola quinqueradiata before and after maturation-inducing treatment by a gonadotropic hormone (GTH). Presence of YAV was examined for various internal organs and gonadal fluids. YAV was not detected from any internal organs examined from fish before GTH treatment. However, neutralizing antibody was detected in the blood of those fish of both sexes. There was no significant difference in the antibody detection rate male and female. On the other hand, YAV was frequently detected from the egg and ovarian fluid and occasionally from the seminal fluid of GTH-treated fish. These results suggest that YAV resided latently in the parental yellowtail reproduced in the sexual products when the fish were matured by GTH-treatment. Thus, it is suspected that YAV is transmitted vertically to the newborn yellowtail fry in hatcheries.
Recent investigations in fish have revealed the dietary dependence of immunosurveillance. This report describes the evidence for dietary link of non-specific cytotoxic activity of natural-killer cells in rainbow trout. Fish were reared for varying periods in different experiments designed to determine the role of protein, essential fatty acid and zinc. Later the immune response was recorded by measuring the release of 51 Cr from labelled P815 mouse mastocytoma target cells after 8h incubation. Leucocytes isolated from the head kidney of experimental fish were employed as effector cells. Dietary protein does not have any effect on the natural-killer like activity of the leucocytes. The activity was low when the diets were deficient in essential fatty acid and zinc.
Serotype and drug sensitivity were studied for vibriosis in ayu Plecoglossus altivelis farms in Shizuoka Prefecture from December 1984 to November 1990. Among 149 strains of V. anguillarum isolated from the diseased fish, 115 (77.2%) and 34 (22.8%) strains were classified to the serotype A (J-O-1) and C (J-O-3), respectively. Serotype C was isolated mostly from cultured ayu raised from seedlings of sea water origin. Fifty one percent of isolated serotype A were from ayu raised from freswater seedligs while other 49% were from those from sea water origin. Serotype C isolates were found from December to May and the most frequently in February. On the other hand, serotype A appeared in January and dominated from June to September. Drug resistant V. anguillarum was most frequently isolated from April to July. Incidence of drug resistant isolates were higher in serotype A than in serotype C. Based on these results, the application of vaccination for ayu seedlings of sea water origin is also recommended. Development of a bivalent vaccine for both serotype A and C is needed.
In 1990, mass mortalities occurred frequently in reared larvae of cockle (Fulvia mutica) in the laboratory of Kyoto Institute of Oceanic and Fishery Science, and a bacterium (strain 90F-1) was predominantly isolated from water of a tank during mortality. Inoculation of the isolate into rearing water at levels of 104 to 105 CFU/ml, killed larvae (95-292μm in shell length) and juveniles (0.7-1.6 mm) of cockles within 2 or 3 days, and inoculated bacterium was re-isolated from these experimentally infected larvae. Thus the isolate was proved to be pathogenic to larval and juvenile cockles. The phenotypic characteristics of the pathogen indicated that it belongs to the genus Vibrio, but it could not be identified as any known species.