Popeye is the bulging or swelling of one or both eyes. Causes: bacterial infection (most common in tank-bred fish), gas-bubble disease (oversaturation), physical injury, or parasitic. Unilateral popeye usually means injury; bilateral often means systemic infection.
If unilateral + clear cause (fight injury): isolate to hospital tank, dose Furan-2 or Maracyn 2 for 5-7 days. Add aquarium salt at 1 tbsp per 5 gallons. If bilateral or unexplained: assume bacterial, dose Kanaplex + Furan-2 combo for 10 days.
Same protocol with marine-compatible meds: Kanaplex + Furan-2 in hospital tank, 10-14 days. Test water for elevated ammonia + nitrate (popeye is often parameter-related). Beta-glucan supplementation supports recovery.
Maintain low nitrate (<20 ppm), quarantine new fish, avoid sharp tank decor that causes eye injuries. Avoid over-aerating to point of gas oversaturation. Feed vitamin-enriched food.
Estimated cost: $30-50.
Mild injury-induced unilateral popeye sometimes resolves with clean water + no medication in 1-2 weeks. Bilateral popeye almost always requires antibiotic treatment - underlying bacterial infection won't clear without intervention.
Mild popeye usually resolves with no permanent damage. Severe cases or untreated infections can cause eye loss or rupture. The fish can survive with one eye but loses depth perception + becomes more vulnerable.
The single most important disease-prevention step: a 4-6 week quarantine of every new fish before adding to your display. See the complete quarantine protocol.