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Some do. For example, the parrotfish sleeps inside a mucous cocoon it makes every night. This blocks its scent from nocturnal predators that might want to eat the parrotfish while it sleeps. Some fishes burrow in the substrate or hide in crevices to rest. Other fishes can’t sleep – they need to keep swimming in order to breathe. Sharks and tuna are among the fishes that can’t sleep.
