Date of this Version
Bacterial gill disease (BGD) was first described by Davis (1926, 1927), who observed it in fry and fingerling brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) in hatcheries in Vermont. The affected trout were kept in dirt-bottom ponds and were not crowded; , daily mortalities were very low. Mortalities rapidly increased when the water temperature increased and diminished when the temperature decreased. Examination of the diseased trout revealed clubbing of gill filaments. In microscopic examination of wet mounts of the filaments" Davis found that the gill surface was covered with closely adhering strands of long, thin bacteria. He called the condition bacterial gill disease, but did not attempt to isolate or identify the bacteria.