What do fish do when sleeping?
While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.
Do fish sleep with their eyes open?
Yep. Fish have to sleep with their eyes open. They don’t have eyelids.
Do fish lay on their side when sleeping?
Overall, when fish sleep, their breathing slows, as does their body movement. If fish go to the bottom of the seabed (or tank, or riverbed), they may even sleep on their side. Loaches have even been known to sleep upside down.