Do fishes sleep?

Do fishes sleep? Tricky question because if many animals (like mammals) sleep during the night and live during the day, sleep in fishes is much more complex! Focus on the unknown aspects of the phenomenon.

A restless sleep

Fishes need to get some rest but this is really hard to notice as they never close their eyes ! They don’t have eyelids as living under water their eye cannot get dry. Some marine animals stay in motion, such as pelagic sharks, which have to constantly swim during their resting time in order to keep breathing thru their branchial arches. It is really difficult to know if a fish is awake or sleeping. Nevertheless, some technics and behavior related to sleep can be noticed.

Diurnal or nocturnal?

Do fishes sleep as mammals, the diurnal or nocturnal activity varies according to species. Many species hunt at nightfall. The green Moreno leaves its shelter looking for fishes, cuttlefish and shellfish using its keen sense of smell. Conversely, the Mediterranean rainbow wrasse as a nightly routine: hiding under the sand to spend the night.

See the green moray

Protection against predators

Many animals feed at night. To protect themselves from predators, preys have developed surprising strategies! The parrotfish as one of the most remarkable one: each night it secretes mucus forming a protector cocoon. This process has many advantages. First, it act as an alarm, when a predator (such as the Moreno) attack the protector cocoon, the Parrotfish can escape. It also has some anti-oxidant properties heal the wound and protect the animal from parasites or ultraviolet ray! This is not the only example of a marine animal which protect itself before falling asleep. The clown fish stick to its anemone, protected from all dangers! In coral reef, some fishes change color during their “sleep” to a more discrete outfit.

See the Orange Clownfish

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