system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 Do fish sleep? if so, then how?

Do they float with their eyes closed? Or like anchor to something?
gpt
Some species do seem to sleep, some don’t.

Species without swim bladders typically can’t, they’ll sink and drown.  They may have periods of inactivity though where they’re lethargic.  Schooling fish and those that live in fast currents can’t either.

Species with swim bladders that lurk in still waters do sometimes exhibit more traditional sleep-like behavior.  They go inactive at night and are unresponsive.  Fish don’t have eyelids so it can be hard to tell.

I had a tank of cherry barbs for years, and they did sleep at night - floating head-down at about a 45 degree angle all night and not harassing eachother or responding to motion outside the tank.