Mucus of salmonids was evaluated as a source for nonlethal detection of the pathogen Aeromonas salmonicida in fish. The bacterium was readily isolated from mucus on dilution plates when Coomassie Brilliant Blue agar was the primary plating medium. Kidney samples from the fish that served as sources of mucus were similarly processed. Infection was detected in 56% of mucus samples from lake trout Salvelinus namaycush that were undergoing an epizootic of furunculosis, but only 6% of the kidneys from these fish were positive for the pathogen. Only 1% of asymptomatic brown trout Salmo trutta sampled at another fish hatchery had A. salmonicida in their mucus, and none had a kidney infection. Combined results from the examination of two pools of Atlantic salmon Salmo salar reared at a third hatchery indicated that 37% of these fish had mucus infections caused by A. salmonicida, but only 4% of the kidneys were infected.

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Although Pseudomonas fluorescens was the predominant bacterium associated with Atlantic salmon (Salmo salar) eggs incubated at the White River National Fish Hatchery (Bethel, Vermont) during January 1992, the fish pathogen Cytophaga psychrophila was isolated only from specific lots of eggs that displayed poor survival (35% eye-up).

Isolates of Flexihacter psychrophila were obtained from chinook salmon Oncorhvnchus tshuwytscha and coho salmon O. kisntch that had previously sustained epizootics of coldwater disease. The pathogen was readily isolated from kidney and mucus of convalescent tish. The organisms were relatively inert in most standard microbiological media but were structurally and serologicalfy homogenous by examination of whole cell protein lysates by sodium dodecyl sulfate polyacrylamide gel clectrophoresis. In contrast to the homogeneity observed in phenotypic and serologic assays, the isolates studied elaborated varied ribotypcs. All isolates produced a single rDNA spacer amplification product of about 240 base pairs.