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Spironucleosis: causes, symptoms and treatment

Spironucleosis (Spironucleus vortens) — etiology, symptoms, diagnosis, active-substance medication, recovery and prevention; mortality without treatment: high.

Overview

Closely related to Hexamita, this flagellate causes systemic disease in cichlids especially angels and discus. Now considered the primary agent of HITH in many cases. Causative agent: Spironucleus vortens. Transmission: water. Incubation: 14-45 days. Reported mortality without treatment: high.

Symptoms

  • pitting on head and lateral line
  • white feces
  • weight loss
  • dark coloration
  • anorexia
  • swelling

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 Spironucleus vortens 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 + improved diet. Metro in food 1% for 7 days plus high-quality varied diet; remove activated carbon during treatment. (duration: 7 days repeat after 14)

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

  • pristine water quality
  • varied vitamin-rich diet
  • minimize chronic stress
  • quarantine cichlids