Yes. Many fish rest with their eyes open because they do not have eyelids that close over the eyes. Fish sleep or enter sleep-like rest in species-specific ways: some hover, settle on the bottom, hide in a shelter, or keep swimming slowly. Scientists identify rest through changes in activity and responsiveness, not by looking for closed eyes.
Why the eyes stay open
Most fish do not have the movable eyelids people use to close their eyes. A few species have structures that partly cover the eye, but an open eye does not mean a fish is continuously alert. The Australian Museum notes that fish show resting patterns even though their eyes generally remain open. [1]
Fish rest in different ways
A resting fish may hover in a protected spot, lie on the substrate, or reduce movement while remaining able to respond to danger. Some species must keep water flowing over their gills, so they rest while facing a current or continue moving. A review of sleep in wild animals describes how fish resting behavior varies and why it is difficult to define using human signs such as closed eyes. [2]
How researchers identify sleep
Researchers look for regular periods of reduced activity and responsiveness, along with changes that resemble sleep across repeated observations. The details differ across fish species, and not every still fish is necessarily asleep. This is why “fish sleep with their eyes open” is a useful short answer, but not a complete description of fish sleep.
Rest is not identical across animals
Fish sleep research is difficult partly because species live in very different environments. A fish that must keep water moving over its gills may use a resting pattern unlike a fish that can settle into a protected crevice.
Other aquatic animals face a different breathing constraint: whales rest while continuing to surface for air. Comparing those strategies helps show why “sleep” is defined by patterns of activity and responsiveness, not one universal posture.
Sources and evidence
- Australian Museum — Do Fishes Sleep? ↗
Fish resting and sleep-like behavior despite open eyes.
- Sleep research goes wild — review of sleep in animals ↗
Comparative evidence and limits for identifying sleep in fish and other animals.
Sources consulted: 15 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Initial publication; the explanation was checked against the linked institutional and research sources, with uncertainty stated where relevant.