Yes, fish do sleep with their eyes open because they lack eyelids; they cannot close their eyes as we do.
Fish have periods of rest typified by reduced activity and response to their surroundings, similar to but separate from human sleep.
During rest, fish may keep their eyes open but reduce their pupils or retain a fixed focus, causing their movements and breathing rate to slow.
Sharks and dolphins use unihemispheric sleep, which allows one brain to sleep while the other remains alert, similar to a night watchman on duty.
Fish require sleep for brain health, physical recovery, and predator evasion, as it aids in information processing, tissue repair, and energy refill.
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