COMPARISON OF THE ENZYME-LINKED-IMMUNOSORBENT-ASSAY (ELISA) AND THE FLUORESCENT-ANTIBODY TEST (FAT) FOR MEASURING THE PREVALENCES AND LEVELS OF RENIBACTERIUM-SALMONINARUM IN WILD AND HATCHERY STOCKS OF SALMONID FISHES IN ALASKA, USA

The enzyme-linked immunosorbent assay (ELISA) and the fluorescent anti body test (FAT) were compared for their sensitivity in detection of Re nibacterium salmoninarum (Rs) in kidney tissues of Alaskan salmonids. The ELISA appeared to be more sensitive in detecting Rs infections. Th e FAT did not detect Rs in 80% of the ELISA-positive samples but was p ositive tor Rs in 28% of the samples that were ELISA-negative. This co ntradiction may have been due to low-level washover of Rs cells from s mears containing large numbers of Rs cells when slides containing mult iple samples were rinsed in a common vessel during the FAT procedures. The FAT routinely did not detect infections in Rs-positive fish the t issues of which produced a mean ELISA optical density value less-than- or-equal-to 0.173, and inconsistently detected infections in fish with ELISA values > 0.173 but < 0.978. The 0.978 optical density was the m ean ELISA value at which the FAT routinely detected Rs-positive fish. Based on the ELISA results, Rs occurred in only 9% of the Alaskan Paci fic salmon tested in both wild (85%) and hatchery (81%) stocks. The ve ry high stock prevalences and levels of Rs antigen detected in wild tr out Oncorhynchus spp., char Salvelinus spp., and grayling Thymallus ar cticus having no clinical signs of bacterial kidney disease suggest th ese species may be somewhat resistant hosts and important freshwater r eservoirs of Rs.