Why does my goldfish keep swallowing air from the top of the water?
Several things cause this type of behavior.
- Lack of food
- Edible surface scum
- Low oxygen level
Tame Goldfish will always beg for food, but if the fish is doing this constantly, even when it isn't feeding time, then it isn't lack of food.
If a container containing Goldfish has no form of aeration or filter, a scum can form on the water surface. This scum is often a form of algae, and being plant life, edible for Goldfish.
If the water is in poor condition, the oxygen level is usually low because bacteria are competing for the oxygen. Check ammonia, nitrate and pH levels. Ammonia also reduces the blood's ability to absorb oxygen and damages gills.
If you are not running a filter, make an immediate, large water change using a water de-chlorinator, as chlorine also damages the gills.
Assuming water conditions are fine, the last reason Goldfish gasp at the surface is gill damage from parasites.
Both flukes and protozoan parasites infest the gills and cause damage. If you suspect this is the cause, read the diseases section of the website, specifically regarding flukes and Costia.
If you make a large water change and the fish stops gasping at the surface, this may only be temporary because of the increased oxygen supply. If it resumes this behavior after a day or two, assume the problem is parasites.