The presence of mycobacteria in salmonoid fishes was first recorded by Earp, Ellis, and Ordal (1) in 1953. Acid-fast bacilli had previously been reported from other cold-blooded animals including fishes of fresh-water and marine origin; recent reviews have been presented by Vogel (2) and Parisot (3).
The initiation of an intensive search for bacteria of this group revealed their widespread distribution in salmonoid fish populations. Acidfast bacilli have been demonstrated in livers and kidneys of salmon and trout in Washington, Oregon, and California, as well as from salmon taken in Alaskan waters. While the organisms are generally considered to be associated with fish of hatchery origin (4), they have also been found in young and adult fish from areas presumably supporting only wild populations. Wood and Ordal (4) indicate that the incidence of the tuberculosis-like infection is directly related to the length of time the fish are reared in the hatchery prior to release. This may result from a common hatchery practice of feeding viscera and carcasses from spawned-out adults to juvenile fish. Therefore, in many instances viable mycobacteria are present in the food of young fish.
