Yes, fish do sleep — though not the way mammals do. They enter periods of reduced activity and lowered metabolism, usually at night, often resting at the bottom of the tank, wedged among plants, or hovering in place. They keep their eyes open because fish have no eyelids.

Here is what normal fish sleep looks like and when resting at the bottom is a concern.

How fish sleep

Fish rest by drastically reducing movement and awareness while staying alert enough to flee danger. Most tropical community fish are diurnal (active by day, resting at night), so they settle down when the lights go off.

Because fish lack eyelids, their eyes stay open during rest — a sleeping fish is not staring at you, it is simply resting.

Where fish rest

• Bottom of the tank — corydoras, loaches and many catfish naturally rest on the substrate.
• Among plants — bettas and gouramis wedge into leaves near the surface.
• Hovering in place — many tetras and danios simply slow down mid-water.
• In caves or under wood — plecos and kuhli loaches hide to rest by day.

When resting at the bottom is a problem

Normal sleep happens at night and the fish resumes activity when lit. Be concerned if a fish lies at the bottom during the day, breathes rapidly, has clamped fins, or is off its food — that signals illness, not sleep. Test the water and see how to save a dying fish.

Frequently asked questions

Do fish sleep at the bottom of the tank?

Many do. Corydoras, loaches and catfish naturally rest on the substrate, while other fish rest among plants or hover mid-water. It is normal at night when the lights are off.

Do fish sleep with their eyes open?

Yes. Fish have no eyelids, so their eyes stay open even while resting. Open eyes do not mean a fish is awake or alert.

Is it normal for fish to lie at the bottom of the tank?

At night, yes. During the day, a fish lying still at the bottom with rapid breathing, clamped fins or no appetite is likely ill and the water should be tested immediately.

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— Jaqline Smalling, FishForever