Hexamita – Protozoan Infection in Fish

At one time, I might have denied that Hexamita could be a serious dermatological pathogen of unexpected species of fish like Koi, goldfish and pond fish. Recently, I have seen cases of severe skin and fin erosion that defied explanation, until the Hexamita organisms were detected in abundance on the surface of the fish. So, YES, cyprinids can suffer from Hexamita infections. We much more expect that Oscars and other big cichlids would.

Flagellated protozoan infections: Hexamita

hexamita erodes skin and fins, and may eat into the skin of the face.
Hexamita erodes skin and fins, and may eat into the skin of the face.

While their presence could have been incidental, it is persuasive that just a pair of treatments using Metronidazole in the water at 500 mg [five hundred milligrams] per ten gallons of water, resulted in complete recovery of the fish.

Is metronidazole, you can get this in SeaChem’s MetroPlex. Use a “nutribullet” or similar blender to emulsify the product and apply per their label instructions. With plain Metronidazole I dose 500mg per ten gallons, once a day for two days then every other day for one or two more dosings.

It is curious to note that the fish recovered completely from the Hexamita attack, but in the process they demonstrated to most profound example of the melanophore migration that I have ever seen. For more on the melanophore migration, please see the ‘Symptoms’ section and refer to ‘color changes’. (Or click here for melanophore migration)

Hexamita is a tiny, flagellated protozoan parasite, which was at one time associated with “Hole in the Head” lesions in the mighty Cichlids and Discus of tropical fish fame. Later research suggested that “Hole in the Head” was a multi-factorial condition, which involved inadequate nutrition, inadequate lighting, and poor water quality. In particular: High levels of background pollution; most specifically: High nitrates and high carbon dioxide levels.

With the realization that the environment was such a big contributor, Hexamita was then downgraded in terms of its role in “Hole In The Head’s” aggressiveness. But with the advent of a few of these more recent goldfish and Koi cases, I am filled with a new respect for Hexamita as (sometimes) a serious threat to Koi, goldfish and pond fish health.

hexamita erodes skin and fins, and may eat into the skin of the face.
Hexamita erodes skin and fins, and may eat into the skin of the face.

The clinical appearance of Hexamita’s attack is principally related to a general lethargy of the fish, followed by significant erosion of the fins and skin. The body may become entirely milky and the slime may come off in strands. The fins begin to look as though the tissue between the rays is being eaten away.

The video version of Hexamita – Protozoan Infection in Fish

Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.