Hexamita (Spironucleus)

Description

• Hexamita
• Spironucleus
• Hole-in-the_Head Disease
• HLLE (Head and Lateral Line Erosion)
• Wasting Disease
• Malawi Bloat

The causative organism for the collection of symptoms making up these diseases was generally believed to be the small intestinal flagellate Hexamita. However, some recent studies indicate that the infecting organism in most cases is probably a very similar flagellate, Spironucleus vortens. The complete lifecycle and transmission of Spironucleus is unclear. However, one way that Spironucleus may be transmitted is via contaminated faecal material. The adult trophozoite multiplies by binary fission in the intestine, and the trophozoites are then passed in faeces. It may also be possible that cysts are produced and evacuated in a similar manner: thus, fish ‘pecking’ at the base of the aquarium are likely to ingest the organism. Post ingestion excystment would occur, if cysts are involved; and/or the newly ingested trophozoites would start to colonise the mucosal surface and mucus layer of the small intestinal lumen – and so the cycle continues.

It has been suggested that, in apparently healthy fish, spironucleus is commonly found in the flagellated stage in the lumen of the upper intestine, where it remains, controlled by the immune system of the fish. In stressed fish, the immune system is placed under greater strain, and the organism, in theory, multiplies unchecked causing considerable localised damage. Once the damage is severe enough the intestinal lining is penetrated and the Spironucleus enters the blood causing systemic and organ infections.

Symptoms

The predominant symptoms of Spironucleus/Hexamita may vary depending on the species infected, and can include:

• darkening in colours
• tendency to hang in corners or to remain isolated from other fish, even at feeding
• decline in appetite
• lethargy
• white, jelly-like excreta trailing from the anal vent
• reduction in muscle tissue and a wasted appearance
• wasted fish may develop a bloated stomach region
• holes and skin lesions may start to appear, especially on the body and the head along the lateral line: these holes may eventually expand and connect to form considerable size ‘craters'

Treatment

The most effective treatment is metronidazole ('Flagyl'), either added to the tank water or administered in food.

To treat the tank, the metronidazole should be pulverised to a fine powder and gradually mixed to a paste by adding tank water. It can then be dispersed in a cup of water before adding to the tank. Treatment consists of:

• 30% water change prior to dosing
• increase water temperature to 30 deg C
• add 250mg of metronidazole per 40 litres of aquarium water (or up to 400mg per 40 litres in severe cases or recurrences)
• after 8 hours, perform a 25% water change followed by another 250mg of metronidazole per 40 litres of aquarium water

This treatment cycle is repeated for three days. Medicated feed is even more effective. However, the recommended dosage of 50 mg/kg body weight for five consecutive days is difficult to measure accurately for small fish such as bettas, and will be impossible to administer if the fish is refusing food.

A vitamin and mineral supplement may be of value in reducing symptoms caused by undernourishment and damage to the intestinal wall.

If an outbreak of Spironucleus occurs, check the water parameters of the affected tank, and ensure that the fish's diet is adequate.

1. Fred Goodall and Dougall Stewart Spironucleus: Hole In The Head and Head and Lateral Line Disease, www.cichlid-forum.com
2. Vicki S. Blazer   Major Infectious Diseases of Fish, Armed Forces Insitute of Pathology.
3. RuthEllen Klinger and Ruth Francis Floyd, Introduction to Freshwater Fish Parasites, University of Florida, Institute of Food and Agricultural Sciences.