Hexamitiasis: causes, symptoms and treatment

Hexamitiasis (Hexamita spp.) — etiology, symptoms, diagnosis, active-substance medication, recovery and prevention; mortality without treatment: high.

Overview

Intestinal flagellate parasite causing weight loss, white stringy faeces, and frequently associated with Hole-in-the-Head disease in cichlids and discus. Causative agent: Hexamita spp.. Transmission: water. Incubation: 7-30 days. Reported mortality without treatment: high.

Symptoms

• white stringy feces
• rapid weight loss despite eating
• darkened color
• loss of appetite
• lethargy
• may precede HITH lesions

Causes

Outbreaks are typically triggered by chronic stress, poor water quality, temperature swings, overcrowding, or the introduction of unquarantined fish. The pathogen spreads via free-swimming or waterborne stages in shared water.

Diagnosis

Diagnosis is based on clinical signs (skin/gill changes, behaviour) and ideally microscopy of a fresh skin or gill scrape, where Hexamita spp. can be seen directly. Differentiate from columnaris, costia, and other ectoparasites that may present similarly.

Treatment

Effective treatment requires isolating affected fish in a quarantine tank, identifying the pathogen, administering the appropriate active substance at the correct dose and duration, and supporting recovery with stable water parameters and nutrition.

Step 1: Quarantine

Set up a bare-bottom quarantine tank with a mature sponge filter, heater, and aeration. Match temperature and pH to the display tank, and acclimate fish slowly. A bare bottom simplifies daily siphoning and prevents medication from being absorbed by substrate.

Step 2: Medication

1. Metronidazole in food. Medicate food with 1% metronidazole and feed for 5-7 days; if not eating, dose water 250 mg per 10 gallons every 24h. (duration: 5-7 days)

Step 3: Recovery

After medication, perform a 30-50% water change and run fresh activated carbon for 24-48 hours to remove residues. Continue feeding a high-quality, varied diet with vitamins and immunostimulants. Reintroduce fish to the display tank only after at least one week without recurrence of symptoms.

Prevention

• high-quality varied diet
• stable water parameters
• avoid overfeeding
• deworm with metronidazole prophylactically for new discus