Fish Gasping at the Surface: Causes, Checks and Emergency Response

Rapid breathing or 'piping' at the water surface usually signals an oxygen or gill problem. Learn the common causes - low dissolved oxygen, ammonia and nitrite toxicity, high temperature and gill parasites - what to test, and how to respond in an emergency.

What surface gasping means

Gasping or 'piping' at the surface - fish crowding the top and gulping - is most often a sign that the fish cannot get enough oxygen across its gills. It is a symptom, not a diagnosis: the underlying cause may be in the water (too little oxygen, or toxic ammonia or nitrite) or in the gills themselves (parasites, bacterial infection).

Common causes (most to least common)

• Low dissolved oxygen (DO). Optimal DO is above 5 mg/L; fish become distressed around 2-4 mg/L and mortality occurs below 2 mg/L. Warm water and overstocking lower oxygen further.
• Nitrite poisoning ('brown blood disease'). Nitrite converts the blood pigment to methemoglobin, which cannot carry oxygen, so fish pipe at the surface even when oxygen is present; the gills may look chocolate-brown.
• Ammonia toxicity. Un-ionized ammonia damages gill tissue and impairs breathing.
• High temperature. Warm water holds less oxygen while raising the fish's oxygen demand.
• Gill parasites and velvet. Flukes, ich or velvet on the gills cause rapid, labored breathing and can leave the gills pale and swollen.
• Bacterial gill disease or columnaris on the gills, which destroys gill filaments.

What to check

• Dissolved oxygen (or add aeration and watch for improvement), temperature, ammonia, nitrite and pH.
• The time of day of any die-off, and whether the whole tank is affected.
• Gill color - brown suggests nitrite; pale or swollen suggests parasites or bacterial disease.
• Whether the largest fish are affected first, which points to an oxygen crash.

First response

1. Increase aeration and surface agitation right away - this is the single most important action during an oxygen crash.
2. Test ammonia and nitrite; perform a large water change (50% or more if ammonia is high) using dechlorinated, ammonia-free water.
3. Stop or reduce feeding and reduce stocking density.
4. For nitrite poisoning, a water change plus adding aquarium salt (chloride) helps block nitrite uptake at the gills.
5. If gasping continues after water quality is corrected, examine the gills for parasites or bacterial disease and treat the specific cause.

Sources: UF/IFAS FA002 (ask.ifas.ufl.edu); Merck Veterinary Manual, Environmental Diseases of Aquatic Animals (www.merckvetmanual.com); Merck Veterinary Manual, Disorders and Diseases of Fish (www.merckvetmanual.com); The Fish Site, Ammonia in Aquatic Systems (thefishsite.com).