Dead or Dying Fish Along Our Shorelines

In the spring, particularly after a strong rain, it is not unusual for residents to observe some dead or dying fish along the shorelines of our lakes.  The fish are infected with Flexibactor columnaris, a common bacterial infection found in many home aquariums. 

Flexibactor columnaris

Columnaris or cotton wool disease, is caused by the bacteria Flexibactor columnaris.  This common bacterial infection effect many of our fish species, but impacts the Centrarchidae in our lakes which include BluegillLargemouth Bass and Black Crappie. It is highly contagious and can spread rapidly.  The bacteria washes into the lakes in the spring from our shorelines and can infect the fish through any small grazes or wounds..

Signs Of Infection

You will see a white film covering various parts of the body of the fish. It is observed mainly on the head but also is seen as fuzz on the fins and gills.  The body of the fish may become ulcerated and the fins frayed. In the latter stages of infection parts of the lips and head may become eaten away. 


Usually only a few of the weaker fish succumb to the infection rapidly.  We do not treat the fish, however, the copper sulfate used to control filamentous algae is also a treatment for Flexibactor columnaris.