Abstract Thirty A tlantic salmon, S almo salar L ., with low corporal condition relative to other fish present in the culture system, were sampled from a freshwater recirculation pisciculture located in C hile. The most characteristic signs and lesions were cachexia and presence of multiple greyish‐white granulomas within internal organs. The external and internal lesions, along with the microscopic, histologic and biochemical findings, were consistent with mycobacteriosis. The identification of M ycobacterium salmoniphilum as the causal agent of the lesions was possible through the use of molecular analyses. This study represents the first report of M ycobacterium salmoniphilum in a freshwater recirculation system and the first case of fish mycobacteriosis described in C hile.