Because the fish itself does not have eyelids, so when sleeping, it can not close its eyes, so it is sleeping with its eyes open. However, most fish stop swimming when they sleep and remain stationary or slightly wobbly in one place. It is worth mentioning that different kinds of fish, sleep time is not the same, most of them rest at night, but there are also some nocturnal fish will sleep during the day, only at night out of activities.
1. Sleeping in the dark: Usually, some common ornamental fish, such as goldfish and snapper, will find a place to hide when they sleep. If there are water plants or stones in the tank, they will often hide in it to rest.
2. Sleeping in the sand: For fish that live on the bottom of the sea, some of them will hide in the sand to sleep. For example, Huahai pig fish, brocade fish and so on, so that rest can prevent the invasion of natural enemies, but also have a quiet environment.
3. Secrete bubbles: In tropical waters, there are some special fish that secrete a gelatinous substance at dusk, which can wrap it up like a sleeping bag, leaving only a mouth opening, so that they can breathe.
4. Sleeping while swimming: There are some special fish that have to swim all their lives in order to breathe normally, and sleeping is no exception, so they can't tell whether they are sleeping or awake.
