Abstract
This paper reports on experiments undertaken to determine whether fluorescent antibody (FA)-based diagnoses of the Renibacterium salmoninarum carrier could be corroborated using a culture method. Preliminary experiments showed that culture could indeed be employed for corroborative purposes because it was more sensitive at detecting R. salmoninarum than the FA technique; the experiments indicated, however, that maximum sensitivity of the culture method was only achieved when the tissue samples were first freed of an anti-R. salmoninarum activity.
Following the preliminary experiments, the corroborative value of the culture method was tested on a field scale with two lots of fish. With a stock of coho salmon (Oncorhynchus kisutch) that was suffering chronic losses due to bacterial kidney disease (BKD), culture proved to be more sensitive at detecting R. salmoninarum carriers than the FA method. With these fish, the method was clearly of corroborative value. With sockeye salmon (O. nerka) that had never had a history of BKD but which possessed anti-R. salmoninarum agglutinins and which were FA-positive for R. salmoninarum, the culture method proved to be of no corroborative value. R. salmoninarum was not isolated even when the sockeye were temperature-stressed and treated with prednisolone acetate to unmask carried pathogens. These observations raise the question as to whether fish carry more than one type of bacterium resembling R. salmoninarum. They also raise concerns about how FA-based diagnoses of the R. salmoninarum carrier should be interpreted. Further studies to investigate these points are indicated.
