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Guppy Disease (Tetrahymenosis): causes, symptoms and treatment

Guppy Disease (Tetrahymenosis) (Tetrahymena corlissi) — etiology, symptoms, diagnosis, active-substance medication, recovery and prevention; mortality without treatment: very high.

Overview

An invasive free-living ciliate that becomes systemic in immunocompromised fish, especially guppies. Commonly observed in inbred or chronically stressed populations. Causative agent: Tetrahymena corlissi. Transmission: water. Incubation: 3-14 days. Reported mortality without treatment: very high.

Symptoms

  • pineconing scales
  • ulceration
  • flashy white patches under scales
  • emaciation
  • lethargy
  • death within days

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 Tetrahymena corlissi 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. Supportive only — poor prognosis. No reliable cure once systemic. Cull severe cases; treat tank with strong water changes, salt 1 tbsp/gal, and formalin baths for milder fish. (duration: weeks)

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

  • avoid inbred guppy strains
  • minimize stress
  • strict quarantine
  • stable water parameters
  • varied diet for immunity