Furnunculosis, a bacterial disease caused by Aeromonas salmonicida, is potentially one of the most devastating diseases in trout and salmon hatcheries. The disease may be controlled by three methods. The most frequently used method of control has been drug therapy. Unfortunately, the bacteria often develop resistance to the specific antibacterial drug. For example, sulfamerazine has been used widely to control furunculosis as well as other diseases. With repeated use in a population of fish, however, the bacteria soon develop resistance to the
drug, thus rendering it ineffective in controlling the disease. In addition, drug therapy usually provides only temporary control and recurrences of the diseaseare very common.