Hexamita sp., Octomitus sp., Spironucleus sp.

Hexamita, Octomitus and Spironucleus are closely related flagellated single-celled protozoans. They belong to the Diplomonadia genera. The pathogenic forms are called, Octomitus intestinalis truttae, Octomitus symphysodont, Spironucleus elegans and Hexamita (Octomitus). Sometimes the Octomitus and Hexamita names are used interchangeably. They share common characteristics and are medicated in the same way.

Hexamita are free-living. The other two are parasitic.

These pathogens commonly affect guppies. They are between 7 and 13 microns. They can infect the intestine, gall bladder, liver and blood. They enter the body through the intestines.

While Hexamita is often associated with ulcers or "Hole in the Head Disease," the parasite may only be a secondary infection, and not a primary cause. Hole in the Head is marked by the formation of holes, ranging from pin-hole sized to large ulcers, in the head and along the lateral line of fish. Hexamita builds up under the skin and musculature of the fish. Eventually the tissue breaks down. The skin breaks open and a whitish, worm-like plug of decayed tissue is discharged, creating a hole. Hexamita and Spironucleus more typically affects guppies as an internal condition and is marked by the wasting away of a guppy.

Hexamita and Spironucleus have occasionally been found in fish that appear healthy, so it is possible for that most guppy breeders have the parasite in their tanks.

Hexamita

Spironucleus looks very similar to the Hexamita. The oval or tear-dropped shape is typical of both, as are eight flagella. They are bilaterally symmetrical.

Spironucleus

Symptoms and Behavioral Signs
The most common signs of a hexamita infection are:
•    lethargy or hiding
•    may turn dark in color
•    mucus-like, pale, thread-like feces that adheres to the guppy for a long time
•    refusal of food
•    wasting away

Diagnosis
Microscopic examination of a squash preparation of the intestine at 200X or 400X magnification. The hexamita move rapidly and erratically. Also examination of the feces.

Causative Condition
Hexamita and Spironucleus are probably spread through aquarium nets (especially in fish stores) and contaminated feces.

The flagellated hexamita make their way to the lumen of the upper intestine, swimming in the fish's intestinal and cecal fluids.

Hexamita may be present in most tanks and shows up when conditions in the tank deteriorate. Guppies become stressed and their immune systems decline. Poor nutrition is another causative factor.

Hexamita have been found living in tanks that contained organic waste but no fish, so they are able to feed off organic waste.

The life cycle of hexamita may be 24 hours. They shed cysts into the feces. It is the cysts ingested by guppies that develop into flagellated adults. They multiply by longitudinal binary division.

Prevention and Treatment
Good maintenance practices in the fish room are the best form of prevention.

According to Doctor Dieter Untergasser, the noted Discus fish doctor, metronidazole is the best cure for hexamita. However, he says that metronidazole does not completely kill hexamita. Some report that the parasite has developed resistance to the medication. See the Disease Library entry for this metronidazole.

A more effective treatment for hexamita may be mebendazole. According to a study by Somboon Sangmaneedet (Spironucleus Vortens of the Freshwater Angelfish Pterophyllum Scalare: Growth Requirements,

Chemotherapeutants, Pathogenesis and Immunity) the drug was found to more effective at killing the parasite (and the hexamitid Spironucleus) than all other treatments (dimetridazole, metronidazole, pyrimethamine, albendazole, fenbendazole, and magnesium sulfate). See our entry for mebenzadole in the library.

Another treatment cited by the literature as effective against these protozoans is dimetridazole when added to the tank water. The dose for 40% dimetridazole is 100mg/L twice at 24 hour intervals.