Sick fish: what do you see?
Start with the water: many fish illnesses follow ammonia, nitrite, a temperature swing or stress. Pick the symptom you see for the likely causes, what you can do today and when to call a vet who treats fish.
White spots like grains of salt
Ich (white spot disease)
Ragged, frayed or shrinking fins
Fin rot
White fluffy or cotton-like patches
Fungus and columnaris
A swollen belly or raised scales
Bloating and dropsy
Gasping at the surface
Gasping at the surface
Fins held tight against the body
Clamped fins
Not eating
A fish that will not eat
Bulging or cloudy eyes
Popeye and cloudy eyes
What this guide does and does not do
It helps you act quickly on the things a keeper can check and change: water quality, temperature, tankmates and isolation. It does not diagnose disease or give medicine doses; follow any aquarium treatment's own label, and for anything serious, spreading or not improving, a vet who treats fish can examine the fish and prescribe treatment. Your local fish store or aquarium society can often point you to one.
The advice follows the Merck Veterinary Manual's chapters on fish and the University of Florida's guide to ammonia; each symptom page links them.
Photo credits
Real photographs from Wikimedia Commons, resized and cropped to fit; each is used under the license named.
- White spots like grains of salt D. Herdemerten Hannibal21, CC BY 3.0, via Wikimedia Commons
- Ragged, frayed or shrinking fins Dizzy Respect, CC BY-SA 4.0, via Wikimedia Commons
- A swollen belly or raised scales Taipan198 at English Wikipedia, CC BY-SA 3.0, via Wikimedia Commons
