Ichthyophonosis: causes, symptoms and treatment
Ichthyophonosis (Ichthyophonus hoferi) — etiology, symptoms, diagnosis, active-substance medication, recovery and prevention; mortality without treatment: high.
Overview
Mesomycetozoan systemic pathogen forming granulomas in muscle and viscera. Typically chronic; transmitted through ingestion of infected tissues. No cure. Causative agent: Ichthyophonus hoferi. Transmission: nutritional. Incubation: 30-120 days. Reported mortality without treatment: high.
Symptoms
- sandpaper texture of skin
- spinal deformity (whirling disease look)
- loss of color
- weight loss
- abnormal swimming
- chronic mortality
Causes
Outbreaks are typically triggered by chronic stress, poor water quality, temperature swings, overcrowding, or the introduction of unquarantined fish. The pathogen spreads via ingestion of infected intermediate hosts (copepods, tubifex, snails) or contaminated feed.
Diagnosis
Diagnosis is based on clinical signs (cottony or fuzzy growths on skin, fins, or gills) and microscopy of a fresh scrape, which reveals hyphae of Ichthyophonus hoferi. Most cases are secondary to injury or pre-existing damage, so search for the underlying trigger.
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
- No effective cure. No reliable medication. Cull symptomatic fish, avoid feeding raw infected fish, freeze feeder fish before use. (duration: n/a)
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
- never feed raw uninspected fish
- freeze feeders 7+ days
- quarantine new stock
- cull symptomatic fish promptly