Using the infectious pancreatic necrosis virus Buhl, Idaho strain (IPNV) which is most of the isolates in Japan, the relationship between the change of quantities of IPNV in infected fry and the disease process was determined under controlled experimental conditions (9.1-14.0°C). The incubation period for IPN was 4 days. Following exposure to the virus, the signs of disease and the first mortality appeared 5 days and 6 days later, respectively. The virus quantities in infected fry were the low level as≤104.1 TCID50/g of fish during the incubation period. The manifestation of IPN was observed at 105.1 TCID50/g of fish and the mortality of infected fry began at≥105.1 TCID50/g of fish, and the following mortality increased parallel with the number of the fry showing≥105.1 TCID50/g of fish.
Anthessius graciliunguis n. sp. is described based on the adult female recovered in the mantle cavity of Mytilus edulis galloprovincialis LAMARCK taken from the Himeji Harbor, Japan. This is the fifth poecilostomatoid copepod known from the blue mussel in Japanese waters. Modiolicola bifidus TANAKA is redescribed based on the newly collected specimens from M. edulis galloprovincialis in Himeji Harbor and Ehime, Japan. The mussel is a new host to M. bifidus.
The changes in blood constituents were examined in ayu, Plecoglossus altivelis experimentally inoculated and naturally infected with Aphanomyces piscicida. The values of blood and plasma constituents except for erythrocyte count and hematocrit value were determined by means of using the unikit of Rapid Blood Analyzer System (RaBA-3010). The experimental infection was done by intramuscularly inoculating into each fish a mass of the hyphae of A. piscicida SA7610 cultured in the FME broth containing 1% of glucose. Necrosis and hemorrhage of the muscle at the site of inoculation and the swelling of kidney and spleen were seen in all fish inoculated. Some of the inoculated fish died within 3 weeks. Statistically significant differences in erythrocyte, hemoglobin, total cholesterol and GPT were found between the control fish and the inoculated fish in a week after inoculation. Levels of erythrocyte, hemoglobin, Al-P, LAP and total cholesterol were decreased after inoculation. On the other hand, levels of GPT and BUN were increased. Significant differences at 5% level between the two groups in 3 weeks post-inoculation were found in erythrocyte, hemoglobin, total cholesterol, albumin, GPT, GOT, LAP, Al-P, TTT and bilirubin. No significant differences were found in hematocrit, total protein, LDH and ZTT of ayu in the course of this experiment. The ayu naturally infected with A. piscicida were taken a pond with an epizootic of mycotic granulomatosis. The ayu were divided into two groups, one with external signs and another without them. Statistically significant differences in hemoglobin, total cholesterol, bilirubin, LDH, Al-P, LAP, GOT and GPT were found between two groups with and without affection. No significant differences were found in total protein and BUN. In affected ayu, levels of hemoglobin, total cholesterol, bilirubin, Al-P and LAP were decreased. On the contrary LDH, GOT and GPT were increased. Significant differences in bilirubin, LDH, and Al-P were found between the ayu without affection and healthy ayu which were collected from another pond without the disease. It was suggested from this fact that changes of bilirubin, LDH and Al-P levels may be characteristics of the early stages of this disease. The levels of total protein, total cholesterol and BUN varied among fish with 3 different sites of affection, nape, trunk and caudal peduncle.
The specificity and rapidity of coagglutination test for the serological typing of IPNV isolated in cell cultures or for the direct detection of IPNV antigen in fish tissues were studied. Coagglutination tests were carried out with cell free virus antigens from selected viruses using Staphylococcus aureus (Cowan I) sensitized with anti-IPNV (Buhl) serum. Positive reactions occured only with cell free IPNV (Buhl) antigen, and no cross reactions were observed. The specificity of coagglutination test for rapid (less than 2h) serological typing of IPNV was tested using the strains from North America, Japan and Europe. Staphylococci sensitized with anti-VR 299 serum gave positive reactions with the strains from North America and Japan (VR 299 type), but did not combine with the strains from Europe (Sp and Ab type). Although staphylococci sensitized with anti-Sp and Ab sera showed weak cross reactions with the strains from North America and Japan, the agglutination pattern was clearly different. The most important use of the coagglutination test for IPNV would be to detect specific IPNV antigen in the internal organs of infected fish. It was found that IPNV antigen could be detected in extracts of IPNV infected rainbow trout (Salmo gairdneri), coho salmon (Oncorhynchus kisutch) and amago salmon (Oncorhynchus rhodurus) tissues at relatively high sensitivity. The results obtained in this study using the coagglutination test for the diagnosis of IPN indicate that this rapid and simple test, which requires no special apparatus and can be performed in the field, is a valuable addition to the diagnostic methods available for detecting this disease.
In vitro and in vivo activities of a potentiated sulfonamide, sulfisozole/trimethoprim (3SI/TMP), against pathogens of yellowtail (Pasteurella piscicida, Vibrio anguillarum, Streptococcus sp.) and those of eel (Aeromonas hydrophila, Edwardsiella tarda) were determined. In vitro results showed that four bacteria except Streptococcus sp. had higher sensitivity to 3SI/TMP than to either of its components. MICs of 3SI/TMP (5: 1) were comparable to chloramphenicol. In vivo efficacy trials in yellowtail and eel, experimentally infected with P. piscicida, V. anguillarum, A. hydrophila or E.. tarda, indicated that 3SI/TMP (5: 1) was fairly active in oral administration. Activity of the combination drug seemed to be superior to oxytetracycline, but inferior to chloramphenicol. Tissue levels in yellowtail of 3SI and TMP were assayed after a single oral administration of 3SI/TMP (5: 1). 3SI appeared comparatively high in blood and kidney, while TMP high in kidney but not so in blood. Both 3SI and TMP were found to have the peak of tissue concentration at 3 or 6 hours post medication, excepting that the highest kidney level of TMP was observed at 12 or 18 hours. Elimination of TMP from tissues of yellowtail and eel administered orally with 3SI/TMP for 7 consecutive days were examined by microbiological assay. Residues of TMP could be detected in their kidneys for a long time.
Chronic mortarities up to 0.2-0.3 % a day occurred in Osaka, Aichi and Nara Prefectures from 1980 to 1981 at some farms of tilapia, Sarotherodon niloticus. Two types of clinical features were observed among the diseased fish. One was characterized by fine white nodules in the spleen and abscesses in the swimming bladder. The other was characterized by hemorrhagic lesions in the gonad, especially ovary. Pseudomonas fluorescens and Edwardsiella tarda were associated with the respective types. These bacteria were proved to kill tilapia by intramuscular injection and to cause essentially the same features as those naturally infected. Ps. fluorescens infection occurred mainly in winter and spring while E. tarda infection took place at warmer seasons. These epizootiological phenomena were supported by experimental infections performed at selected water temperatures. The mortalities of tilapia due to Ps. fluorescens and E. tarda became highest at 15-20°C and at 20-30°c, respectively.
During the period from mid June through late July 1983, a massive mortality of oval filefishes (Navodan modestus) was found throughout the western region of the Iki channel. Visible characteristic lesions were not observed on the 14 dead fish collected for bacteriological examination, but a bacterium was isolated from the kidneys of all the fishes tested. By comparing the characteristics of the present isolates with these of the isolate from pseudotuberculosis of cultured yellowtail (Seriola quinqueradiata), the present isolates were identified as Pasteurella piscicida. Four oval filefishes which were intramuscularly injected with the representative isolate caused 100 % mortality within 48-72 h after injection. The pathogenicity of the isolate to yellowtail was confirmed by injecting with it after fish passages, but formation of white tubercles in the internal organs, known as a characteristic lesion of bacterial pseudotuberculosis of yellowtail, was not observed. In conclusion, it was confirmed that the high mortality of the wild oval filefish was caused by P.piscicida infection.