Emergency · Fish & aquariums
Fish gasping / oxygen crisis
Fish crowding the surface or gasping usually means low oxygen, toxic water, or gill damage.
Immediate safe actions
- Increase aeration immediately: air stone, lower the water line to splash, or point filter output at the surface.
- Test ammonia, nitrite, nitrate, pH, and temperature.
- Do a 25–50% water change with dechlorinated, temperature-matched water.
- Check that heaters and filters are working; reduce temperature slowly if too warm.
What NOT to do
- Do not add medications before testing water.
- Do not do 100% water changes or sudden temperature swings.
- Do not feed until fish recover.
Information to gather for the vet
- Full water test results
- Tank size and stocking
- Recent changes (new fish, decor, cleaning, medications)
- Power outages
Red flags
- All fish gasping
- Red or bleeding gills
- Fish lying on bottom, rapid gill movement
Veterinary escalation
- If water fixes don't help within hours, contact an aquatic vet.
General educational information only. Species differ greatly — always confirm with a licensed veterinarian or animal poison service.