Al Sabetta February 1, 2002

Hexamitiasis is an internal protozoan infection that can afflict most species of fish. It is caused by free swimming protozoan organism known as Hexamita (formerly known as Octomitis). This parasite is described as clear, size is approximately 10 micron, possesses 8 flagella for locomotion, and can be seen under a microscope @ 200 - 400X power. Post mortem identification is made by making a squash prep of the intestinal lining, but it is also possible to detect in the feces, and in the shed mucosal lining.

Most fish can harbor this pathogen in small numbers in their intestinal tracts and show no symptoms whatsoever, but there are certain species of fish that are prone to serious illness when infected. Among this group are discus, angels, oscars, and African cichlids in general. Fish harboring this pathogen in low levels can have it become a serious infection if subjected to stressful conditions such as overcrowding, poor water quality, poor nutrition, bullying by other fish, weakened immune system from other infections. Under these conditions the affected fishes immune system can not adequately control the parasite and it reproduces rapidly causing the acute disease hexamitiasis, fondly known as Hex.

Symptoms include the following:
The first indication is a slimy whitish feces. This feces has components of the mucous lining of the intestine in it. Fish exhibiting this symptom will still be eating normally at the early stages of the disease. As the disease progresses the fish will often exhibit nontypical behaviors such as hiding in the corner, head down. The fish may stop eating and become emaciated. Laterally compressed fish like discus often show this emaciation in the head region. The bodies and eyes of the fish often darken. The fish may swim backwards, or swim listlessly.

Disease transmission is by contaminated fecal matter. Cleanliness of the tank can be a major factor in the transmission of the disease.

Most authorities recommend using the drug Metronidazole to treat this illness. It is available at pet shops under commercial names such as Hexout, Hex-a-mit, etc. It is also available by prescription as the drug Flagyl. The dosage recommended is typically 250 mg/10 - 20 gallons aquarium water. The drug is absorbed through the gills, and works systemically. Remove carbon during treatment, maintain biological filtration. The medication is given every other day with 50% water changes between, for a total of 3 - 5 treatments. Watch water for sign of water fouling as the medication is in a sugar base and bacteria can proliferate. If the affected fish is still eating, it may be given in the food at a dose of gram/4 ounces food. This is an excellent way to treat the illness. A week of such treatment is usually required. Feed only medicated food during this time.

A note on treatments: this disease is a very common illness of fish. If you are treating it be sure to fully treat the fish. There is a very real problem with the evolution of resistance to medications. Many hobbyists have been reporting hexamita that seems resistant to the drug metronidazole. They are reporting the need to use a higher dose to cure the ailment. This is a concern because of toxic side effects of Metronidazole at higher doses.

Among some groups of hobbyists there is also a treatment for Hexamita that uses higher water temperature. Discus and angelfish owners report that elevating the water temperature to 92 - 100 degrees F. "cures" the disease. If your fish can tolerate that temperature it may be worth trying.

Hexamita and Hole in the Head disease. The parasite has been associated with Hole in the Head disease and Lateral Line Erosion in some species of fish. There are even commercial medicines to treat these illness that are treating them using metronidazole. The general consensus is that these illnesses are nutritional deficiencies, and the causes for them are highly variable. Any disease state interfering with the uptake of vitamins or minerals is suspect. That includes protozoan infections like Hexamita, and infection by nematode worms such as Capillaria. The nutritional cause may also be lack of certain vitamins (B and D -complexes author's guess) that are related to foods being fed, and not disease at all. In short, the illnesses are not fully characterized yet.

Personal note: since Hexamita is so common it is highly recommended to suspect all new fish of having it, and treat new fish prophylactically in quarantine before adding them to your tanks.

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