Dead fish in your lake?


The most common disease occurring in lakes is caused by the bacterium Flavobacterium columnare. This pathogen causes large kills of sunfish, crappies, and bullheads in late spring and early summer. Infections in metro area lakes usually start around Memorial Day weekend and persist until early July.

The bacterium exists naturally in fish populations and expresses itself when stressful conditions exist. The infection is brought on most commonly when water temperatures increase rapidly. The increase in water temperature often brings an increase in spawning activity, which coupled with stress caused by temperature changes, make the fish more susceptible to the infection.

Fish infected with Chondroccus columnaris are characterized by eroded gill tissues, with a grey-white to yellowish slime on the skin, gills or fins. These kills occur on most metro area lakes, and may involve several thousand fish in some years. In most cases, the numbers lost are small in relation to the total population, and no change in angler success can be attributed to columnaris disease.

Live fish infected with this infection are edible. Fish caught with columnaris should be skinned and prepared as desired. Fish should be cooked to a temperature of 140 degrees F. for at least five minutes before eating.

Chondroccus columnaris infected fish sometimes suffer a secondary infection caused by the fungus Saprolegnia. This fungus appears as a white, cottony growth on the body of the fish. This furry or hairy appearance disappears when the fish is removed from the water.

This fungus can kill fish by completely covering it. There is no danger to humans, but a bad taste may develop as a result of the infection. Fish infected with Saprolegnia should be skinned with the infected areas cut out, then prepared as usual.