Goldfish are amusing pets that display many different types of behavior, such as swimming at the top of the water when you approach the tank in anticipation of feeding time. Like all animals, goldfish need to have periods of rest in order to conserve energy. When a goldfish hovers in the corner of the tank and moves her fins only occasionally, it may be that she is resting or sleeping.
It is difficult to tell exactly when your goldfish may be sleeping, as goldfish have no eyelids and not all goldfish sleep the same way. However, a sleeping goldfish may hover at an angle with her nose tilted down toward the bottom of the tank, or she may hover in a more normal swimming position with her dorsal fin half erect and her front pectoral fins moving slowly. Some goldfish will float lazily in the middle of the tank or hover just above the bottom substrate of the tank. Some goldfish will rest in small groups, while others will hide in the cover of aquarium decorations or between aquarium plants.
Sleep vs. Resting
At the time of publication, the subject of sleeping goldfish had not been thoroughly
studied, so it is unclear whether goldfish merely enter a resting state to save energy or actually enter a sleep cycle in which they are less aware of their surroundings. Fish brain wave patterns indicate that fish do not enter REM sleep like mammals do and that some do not lose consciousnesses during sleep.
Keeping Goldfish Healthy
Goldfish can sleep during the day or at night when the tank light is turned off. Providing a regular day/night cycle for your goldfish will help her rest -- which is thought to reduce stress caused by too much activity or light stimulation. Just like people and other animals, a goldfish needs to have a period of night. Since a goldfish has no eyelids, she can't close her eyes to block out the light, so it's important to give your goldfish a dark environment in order for her to sleep.
Signs of Sick Goldfish
There are times when hovering behavior may be not a sign of sleeping but of an illness or a chemical imbalance in the tank water. If your goldfish is hovering upside down in the corner of the tank, she may have swim bladder disease. When a fish is hovering in an upside down U-shape in the corner of the tank, it means the nitrate level of the water is too high. This is a dangerous tank water condition that needs to be dealt with immediately, as nitrates are toxic and can kill your goldfish.
- Photo Credit gold fish with red cap image by Daria Miroshnikova from Fotolia.com