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By Dr. Laurie Hess, DVM, Diplomate ABVP (Avian Practice)
Goldfish are extremely popular pets, whether they are living in a fish aquarium inside a home or a pond outside in a yard. But there is one question that goldfish owners often ask—do goldfish sleep?
Goldfish do not have eyelids and cannot close their eyes, but they do, in fact, sleep—just not in the same way we do.
What Do Goldfish Look Like When They Sleep?
Unlike people, goldfish do not lie down when they sleep. Rather, they become less active, staying in one place and moving slowly to keep themselves stable. They look like they are hovering in the tank or pond, usually low in the water, an inch or so off the bottom, with their heads pointed slightly downward. Their color may fade a bit while they are sleeping and will return to normal when they are awake. They change color as a safety measure to hide themselves from predators when they sleep. Finally, goldfishes’ brainwaves don’t change when they sleep, and goldfish don’t enter into periods of deep, REM sleep, as people do.
When Do Goldfish Sleep?
Goldfish don’t naturally sleep at night, like people do. They do sleep better when it’s dark and quiet, so many fish will sleep at night. If you make noise around a sleeping fish, it will startle awake. Thus, it’s best to keep the noise level down when your fish wants to sleep. If you keep a light on in the tank, you can train fish to sleep at night, when you sleep, and stay awake during the day. If you turn on and off the light at the same time every day, goldfish will typically follow the same sleep pattern. The light should not be on for more than 12 hours a day, or fish may not get enough rest. If it isn’t dark enough for them to sleep, they may hide in plants to seek out darkness to try to sleep.
What Happens When Fish Don’t Get Enough Sleep?
Just like people, fish need sleep to restore energy to their body systems and to maintain proper immune function. If they don’t sleep enough, they lose their ability to fight off infections and their metabolism slows.
How much sleep they need depends on the fish. Some goldfish nap in the afternoon, while others stay awake until night time. Being exposed to regular day and light cycles is essential to fish getting enough sleep and remaining healthy. Finally, yawning isn’t a sign of tiredness in fish but rather is just the fish clearing its gills with water.
How Can You Distinguish a Sleeping Fish From a Sick One?
Sleeping fish remain stationary but upright; they do not turn sideways or upside down. A fish that is leaning, is upside down, or lying on the bottom isn’t sleeping but is likely sick. Fish with disease of the swim bladder—the organ that helps them keep buoyant—will often float sideways or upside down and have problems swimming. Lying on the side also may be an indication of a bacterial infection or high concentrations of nitrite or ammonia in the water. Regardless, if a fish owner sees his fish floating sideways or upside down, he should have the fish checked out by a veterinarian as soon as possible.
So, if you see your fish hovering above the tank floor, looking a little pale, turn off the light, turn down the noise, and let him have a power nap. He will be healthier and happier for it.