The peroxidase-antiperoxidase (PAP) procedure, modified enzyme immunoassay was applied to the detection of Renibacterium salmoninarum. This method did not indicate any cross reactivity with other fish pathogens, and was specific to BKD. The sensitivity of this proceudre was 1 × 103 cells/ml which was at least 10 times greater than the indirect fluorescent antibody technique. The PAP procedure was tested in a BKD survey, and gave excellent results when compared with other diagnostic procedures.
Coho (Oncorhynchus kisutch), chum (O. keta), masu salmon (O. masou) and rainbow trout (Salmo gairdneri), which survived experimental infection with Oncorhynchus masou virus (OMV), were observed for the development of tumors induced by OMV. Tumors in coho and chum salmon were first observed 120 days post-infection and after 200 days, 35 % of the coho and 40 to 60 % of the chum salmon were affected. The rate of tumor induction was not influenced by the age of the fish at the time of infection. Tumors of rainbow trout and masu salmon were not present at 200 days post-infection but appeared after 240 and 270 days, and the rate of tumor inducement reached 12 % for rainbow trout and almost 100% for masu salmon after 365 days. Tumors occurred mainly around the mouth, but were also observed on the fins, opercula, body surfaces and corneas of the eyes. Histopathologically, the tumors were composed of abundantly proliferative, well differentiated epithelial cells supported by fine connective tissue stroma. OMV was recovered from the culture medium of one passage of the transplanted tumor cells by primary culture series.
The molecular taxonomy of representative strains of gliding bacteria classified into two groups as Flexibacter maritimus (Group I) and Flexibacter sp. (Group II) in a previous report was determined. The average percent guanine plus cytosine (% G + C) of the deoxyribonucleic acid (DNA) of Group I was 32.24 which was within the range reported for F. maritimus. Though Group II had lower% G + C of 29.38, it was not significantly different from that of Group I. Polynucleotide sequence analysis determined by optical measurement of renatured DNA showed high homology values from 92 to 100 % among strains of Group I and Group II. In addition, the average similarity value derived from numerical taxonomy study was 82.7%. Based on these results, the two groups of gliding bacteria isolated from diseased cultured flounder are considered to belong to the same species of F. maritimus.
Anatomical and histological studies were made on the distributions of Fusarium solani in kuruma shrimp, Penaeus japonicus, which were naturally and experimentally infected with the fungus. Hyphae and tissue destruction due to fungal infection were observed in the gills of all the naturally and experimentally infected shrimps examined. They were also frequently obseved in the maxillipeds, pereiopods, thoracic body wall, thoracic central nerve and occasionally in the ventral thoracic artery. Hyphae were seldom or never observed in the other organs examined. The gill conditions of the dead or moribund shrimps could be classified into the following two types. 1) Entirely blackened gill. This condition was observed mainly in the shrimps which died within a short period after infection. All the gills were severely infected with the fungus and blackened. The gill tissues were degenerated and the hemal channels were obstructed with hemocytes, hyphae and tissue debris. Failure of gas exchange in the gills was thought to be the main cause of death in this condition. 2) Partially blackened gill. This condition was observed in the shrimps which died long after infection. Most of the gills were partially affected with the fungus and blackened. Destruction of the gill filaments was rather rare, but the fungus penetrated into the thoracic body wall which collapsed. The hyphae infected further the thoracic central nerve and ventral thoracic artery. In this condition, in addition to respiratory failure damage of the central nerve and the ventral thoracic artery was thought to be responsible to death.
Application of erythromycin (EM) to control natural-occurring streptococcicosis caused by β-hemolytic Streptococcus sp. in cultured rainbow trout, Salmo gairdneri was investigated.β-hemolytic Streptococcus strains were isolated at high frequency from diseased and apparently healthy fish collected from the pond. These isolates indicated a strong sensitivity against EM at in vitro sensitivity test. Fish population transferred from contaminated pond were fed with pelleted food containing EM at a dose of 50 mg/kg/day for 5 days. After the drug was administered to the fish population for 5 days, the mortality was markedly reduced during the observation period. Therefore, EM was confirmed to be an effective drug for the control of streptococcicosis in cultured rainbow trout.