Check water first
Test temperature, ammonia, nitrite, nitrate and relevant source-water changes. Husbandry problems can mimic disease and must be corrected.
Separate the affected fish
Use a stable hospital tank when possible to reduce spread and improve observation.
Document signs
- When the change began.
- Appetite and waste.
- Breathing rate and gill movement.
- Swimming, buoyancy and posture.
- Skin, fins, eyes and swelling.
- Recent additions, treatments or equipment failures.
Seek qualified help
Contact a veterinarian experienced in fish medicine for diagnosis, humane euthanasia or prescription treatment.
Protect people too
Wash hands after aquarium work, cover cuts and avoid cleaning aquarium equipment in food-preparation areas.