Do Not Disturb: Sleeping Fish

by B. N. Sullivan

Pygmy Toby (Canthigaster pygmaea)We all need our rest, and so do the fish in the sea. Fish don't sleep exactly like we do. For one thing, they don't have eyelids, so they can't close their eyes. Nevertheless, most fish we know about do take their rest for some part of the day or night, on a fairly regular schedule.

Some fish -- especially pelagics -- hunt at night, and rest during the day. Most reef fish are very busy during the day, so they rest at night. They stop moving about and enter a sleep-like state. While they are resting, they are generally sluggish and not very alert. We try our best not to startle them or disturb their rest during our night dives.

Some fish lie on the bottom to rest, while others hang motionless in the water column. Small fish, in particular, often hide while they are in their somnolent state so that their predators can't find them and eat them. Staying out in the open to rest definitely would give their predators an unfair advantage. In the first photo on this page, a tiny fish called a Pygmy Toby (Canthigaster pygmaea) has snuggled itself amongst corals and sponges to "sleep."

In the second photo, a small fish has chosen to settle into a stand of fire coral to takes its rest. We're not sure what species of fish this is, although the shape suggests that it is some kind of Damselfish.

Fish hiding in Fire CoralIn addition to hiding, another strategy that many fish use to discourage predation while they rest is to change color. Their color may darken or become mottled during periods of rest, helping them to blend in with their environmental background.

Some species of Parrotfish hide themselves by spinning a slimy cocoon around themselves. The mucous cocoon is secreted from an organ in the head of the Parrotfish. (Sorry, I don't have a photo handy.) It is thought that, in addition to hiding the fish, the cocoon also masks the animals' scent, making it harder for predators to locate them.

Both of the images on this page were captured during night dives in the Red Sea, along the coast of the Sinai Peninsula.

7 comments:

  1. I think I need to start sleeping like these fish! Great info here and never knew this about fish!

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  2. The first fish looks quite comfy in his little spot!

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  3. @ Mon@rch - We're pleased to have shown you something new.

    @ Kathy - He does look comfy -- all snuggled in.

    Bobbie

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  4. Too bad that I am not a scuba diver. The snorkeling on the surface of the water does not allow for looking at such ocean life details but hey it's fun too.

    Mahalo for showing us the hidden water world. Aloha, Pua

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  5. So wanted to dive - but didn't pass the medical to get my divers license. so it's great to come across websites such as yours to enjoy. Great pics.

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  6. @ Pua - Snorkeling is the next best thing to diving. ;-}

    @ Treehouse & Flippers - Thank you. I'm glad you're enjoying the photos.

    Bobbie

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We welcome your comments and invite your questions. Dialogue is a good thing!

Bobbie & Jerry