Fish Diseases

Infections & Parasites

In This Section


Columnaris Disease

The affected skin may have pale patches and/or a characteristic sore or lesion shaped like a saddle across the dorsal fin.


Flukes (Black, Yellow, and White Grubs, Eye Flukes)

Fluke larvae burrow into the flesh of the fish and form a cyst.

Largemouth Bass with Melanosis

Melanosis (Black Spot, Blotchy Bass)

Melanosis is not an infection but an increase in the melanin in the skin.

Fish roundworms in body cavity

Fish Roundworms

Red, off-white, and white worms found under the skin, in the intestines, and in the body cavity.

Sandy Flesh

Sandy Flesh

The diseased flesh appears tough, granular, coarse, and yellow to brown, often resembling freezer-burned meat.

Tapeworm Larvae

Fish Tapeworms

Tapeworm larvae (plerocercoids) often appear as white cysts or coiled worms in the flesh or internal organs.

Fish Ulcers

Fish Ulcers

The most common causes are three bacteria in the genus Aeromonas.

Fish Warts

Fish Warts

Fish have wartlike growths on the skin, fins, and occasionally gills.

Water Mold

Water Mold

Water molds (which are not true molds or fungi) appear as white, gray, or tan cottony growths on the skin of the fish when submerged in water.