RELATIONSHIP BETWEEN RESISTANCE OF SALMONIDS TO FURUNCULOSIS AND RECOVERY OF AEROMONAS-SALMONICIDA FROM EXTERNAL MUCUS

Fish were sampled at the Ed Weed Slate Fish Hatchery (South Hero, Verm ont, USA) in September 1992. Aeromonas salmonicida was common, with co ncentrations as high as 10(5) to 10(7) colony-forming units per gram o f mucus, and readily recovered from most mucus samples obtained from f urunculosis-sensitive populations of brook trout (Salvelinus fontinali s), lake trout (Salvelinus namaycush), and Atlantic salmon (Salmo sala r). The pathogen was the predominant microorganism and accounted for g reater than 85% of the total number of bacteria isolated from the mucu s of these fish. By comparison, A. salmonicida was recovered only from two rainbow trout (Oncorhynchus mykiss), and bacterial frequencies di d not exceed 10(3) colony-forming units per gram of mucus. The pathoge n was not recovered from the mucus of steelhead (O. mykiss) or Rome br own trout (Salmo trutta) selectively bred for resistance to furunculos is, even though there was widespread contagion throughout the hatchery and fish were cultured on a common, unprotected water supply.