In an aquarium, gas exchange occurs where the air and water meet. This means the oxygen concentration is usually highest near the surface. Fish who struggle to breathe or absorb oxygen may seek out this area to ease their oxygen deprivation.


If your fish linger near the top of the tank or next to the airstone's bubble eruptions, their environment may be out of sync - check your aquarium's pumps, filters and test the water. Elevated ammonia levels inflame gill surfaces, and nitrite poisoning prevents red blood cells from transporting oxygen. The presence of chlorine and a pH levels that are too high or too low will make fish gasp at the surface.

Fish with damaged gills also may exhibit breathing difficulty. Why? Your fish's gills act as his lungs, exchanging carbon dioxide waste for oxygen molecules. Before you panic, be sure the affected fish aren't a species that breathe atmospheric air, such as bettas and true gourami.

When disease-causing organisms irritate gill tissues, the fish's body sends inflammatory cells to the area. This cellular infiltration can also impair the gills' function. Causes include ich (or white spot disease) and bacterial infections.

Larger parasites, such as gill flukes, actually destroy the gill surface as they attach and feed. If you see your fish holding his fins close to the body, rapidly flaring the gill cover, or swimming lethargically, he may have a gill and respiratory problem. In any of these cases, you must act quickly to save your fish's life.

What You Can Do at Home

First test your aquarium water for common abnormalities, such as ammonia, nitrite and pH imbalances. Your local Petco or veterinarian can run these tests if you don't own a kit. Also make sure your heater, filter and air pump are working properly.

Next, change 25-50% of the tank water and siphon debris from the gravel to improve biological filtration. Be sure to dechlorinate water and match the temperature and pH. This simple routine will dilute the pollutant or disease organism in the tank and give you time to identify your pet's problem.

When to Call the Veterinarian

If water analysis doesn't yield the answer, consult a qualified fish veterinarian right away. She or he may examine your fish, recheck your water parameters and take a thorough medical history. You veterinarian may also recommend gill biopsies and blood tests.

If your fish dies, don't dispose of his body right away. You may be throwing away evidence that could save the rest of your fish. An aquatic veterinarian can perform a necropsy (an autopsy for animals) with tissue from your deceased fish.

If you can't find an aquatic veterinarian in your area, consult an Aquatics Specialist at your local Petco for advice. Researching the condition on your own may be a last resort as speaking with an experienced aquarist is usually the most helpful; however, there are a lot of books that offer good information.

Many diseases can cause breathing difficulty, but this condition can be life-threatening - so act fast. After you identify and treat the problem, you and your pet can breathe a sigh of relief.