DIFFERENCES IN DETECTION OF AEROMONAS-SALMONICIDA IN COVERTLY INFECTED SALMONID FISHES BY THE STRESS-INDUCIBLE FURUNCULOSIS TEST AND CULTURE-BASED ASSAYS

Accurate detection of Aeromonas salmonicida subsp. salmonicida (the ca use of furunculosis disease) in covertly infected salmonids is difficu lt and is a cause of concern for those involved in fish health inspect ion and resource management programs. In this study, we examined popul ations of brook trout Salvelinus fontinalis, Atlantic salmon Salmo sai nt; and lake trout Salvelinus namaycush that previously sustained natu ral episodes of furunculosis. Consequently. the sampled fish were pres umed to harbor latent infections. Mucus, gill. liver, kidney, heart, s pleen, and intestine samples (N = 100 fish per group sampled) were pro cessed and examined by (1) diner dilution counts and (2) quadrant stre aking after a 48-h pre-enrichment in trypticase soy broth (TSB). Anoth er subsample of fish from each group was then subjected to stress-indu cible furunculosis tests. Stress tests detected A. salmonicida in thre e of four groups of fish that were examined whereas the pathogen was d etected in only two of the groups analyzed with culture-based assays. Although pre-enrichment in TSB enhanced detection within internal samp ling sites including the liver, heart, spleen, and kidney, enrichment did not enhance detection from mucus, gill, or intestinal samples.