A fish inside a cocoon
As night falls, some parrotfish hide among the rocks. A layer of mucus wraps around the fish like a thin bag. It can keep tiny parasites from reaching the fish.
Waiting for prey or sleeping?
Look at the scorpionfish. It stays still while waiting for prey. A sleeping fish can also stay still, even with its eyes open. You need more clues to tell what it is doing.
Making up for lost sleep
A resting zebrafish may take longer to react to a signal or respond less often. In some experiments, zebrafish slept more after researchers kept them from resting.
Waves in the brain
Scientists watched what happened inside the brain of a sleeping zebrafish. They saw two patterns. In one, short bursts of activity came and went slowly. In the other, activity spread like a wave.
