The parrotfish’s secret
In an experiment with Chlorurus sordidus, researchers compared gnathiid attacks on fish with and without cocoons. The difference between the two groups suggests that the cocoon protects against parasites. It does not establish the fish’s state of alertness inside the cocoon.
The puzzle of open eyes
Both a scorpionfish in ambush and a sleeping fish can stay still. In behavioural sleep, activity falls and it takes a stronger stimulus to elicit a response. The fish can also return to normal activity quickly when roused.
Does the zebrafish make up for lost sleep?
Sleep rebound is an increase in sleep after deprivation. Researchers have observed sleep rebound in zebrafish under certain experimental conditions. A lack of rebound under another protocol is not enough to rule out sleep.
The night the brain gave up its secret
The 2019 study combined neural imaging with measurements of eye movements, muscle activity and heart rhythm. The recordings distinguished slow, recurring bursts of neural activity from a wave that spread through the nervous system. The two states share some features with mammalian sleep, and the resemblance is partial.
