Fishy sleeping bag

Although fish have no eyelids and cannot shut their eyes, they still rest and sleep. Some sleep buried in the sand, others seek out a crevice or tangle of seaweed safe from marauding night time predators, while the little clown fish found in tropical coral reefs is covered with a special mucus that allows it to hide among the poisonous tentacles of a sea anemone.

Yet no sleeping place is stranger than that of some species of parrotfish, which spend the night in a sleeping bag. These members of the perch order of fishes are robust and blunt-headed, and measure up to 1.2 m (4 ft) long.

Often coloured in bright shades of blue, green, yellow, orange and red, they are found in tropical and subtropical coral reefs worldwide. As they settle down for the night among the corals, they secrete from their bodies a transparent cocoon of sticky mucus that surrounds them. This process takes up to half an hour, and a similar amount of time is needed for the fish to free themselves in the morning.

The parrotfish do not produce their sleeping bags every night, and the bags' function is still a mystery, though it is possible they prevent predators, such as moray eels, from detecting the parrotfish's scent.