What does Uronema marinum (Uronema marinum) look like?

Yellow/red ulcer. Frayed/torn fins. Rapid breathing.

How is Uronema marinum (Uronema marinum) treated?

Formalin bath (37%): Most effective. 45-minute bath in 1 tsp formalin per 1 gal aerated saltwater. May need 2-3 baths 48h apart for severe ulcers.

SALTWATER disease

Uronema marinum (Uronema marinum)

Reviewed by the Fast Aquatics husbandry team · Updated May 2026

Quick referenceUronema marinum is a free-living scuticociliate that becomes parasitic in stressed marine fish. Causes red ulcers + rapid death; treat with formalin baths and improved water quality.

Symptoms

Yellow/red ulcer
Frayed/torn fins
Rapid breathing
Surface gasping
Refusing food
Bulging eye(s)
Hidden lesions under scales

Cause

Uronema marinum normally lives free in sea water. Becomes parasitic on stressed, weakened, or wounded fish. Common in low-salinity (under 30 ppt) tanks where fish are immunocompromised. Often strikes anthias + chromis after shipping.

Treatment options

Formalin bath (37%). Most effective. 45-minute bath in 1 tsp formalin per 1 gal aerated saltwater. May need 2-3 baths 48h apart for severe ulcers.
Furan-2. Backup for secondary bacterial infections. Treats opportunistic infections in ulcers.
Raise salinity to 35 ppt. Hyposalinity (under 30 ppt) makes fish vulnerable. Get back to natural reef salinity (35 ppt) gradually.
Improve water quality. Test ammonia + nitrite + nitrate. Reduce stocking density.

Always treat in a separate quarantine or hospital tank. Most medications are toxic to coral, invertebrates, and live rock biology. Consult an aquatic veterinarian for valuable fish.

Prevention

Maintain salinity at 35 ppt. Reduce stocking density - over-crowded tanks have higher uronema rates. Quarantine new fish (especially anthias + sensitive species).

Fatality + outcome

Moderate to high - 30-60% of infected fish die without treatment. Aggressive variant kills in 48-72 hours.

Full disease database · Symptom matcher · Q&A library · Glossary · QT timeline calculator

Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.