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Swim Bladders and Giant Bellies

Category: General Article

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Friday, December 8, 2017

Summary: Researcher April Cook looks at two particularly unusual adaptations of deep sea fish — one that deals with buoyancy and another helps them process food in a nutrient poor environment.

My name is April Cook and I study a family of fishes known as swallowers or snaketooth fishes (Family Chiasmodontidae). Their closest relatives all live in shallower waters. But swallowers have adapted to living in the deep, dark sea.

One adaptation to deep-sea life is the loss of their swim bladder. A swim bladder is like a balloon inside a fish. The swim bladder fills with air to help the fish float (buoyancy). A swim bladder allows the fish to move up and down without having to use a lot of energy moving their fins. Take a look at the illustration of the hatchetfish to see how a swim bladder works.

Almost all shallow water fish have swim bladders. Most deep-sea fish do not have swim bladders due to issues with pressure. As you go deeper in the ocean, the pressure increases which causes air to compress. This would make an air-filled bladder useless to a deep-sea fish. Instead, deep-sea species have developed body structures which work like hydrofoils. If a deep-sea fish wants to change its depth, it does so by letting the water moving across these structures lift their body through a process called hydrodynamic lift. This is a less efficient method for changing depth, however, so deep-sea species are usually slower and less agile than their shallow water counterparts.

Another adaptation to life in the deep sea is the swallower’s ability to distend its stomach to the extreme!

Are they the gluttons of the sea? No, but food is scarce or hard to find in the deep sea. Animals have adapted to this by taking advantage of any meal that they may come across — no matter how large. In order to be able to eat a meal this large, swallowers’ mouths have adapted to open much wider than most other fishes. Swallowers have many rows of sharp teeth. Their stomachs can expand to several times their normal size. We capture a lot of swallowers with full bellies, which can be a very dramatic sight!

Take a look at the photos on this page and you’ll see what I mean!

Thank you for joining us on this DEEPEND mission. We hope you enjoyed this exploration of discovery!

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Creep Into the DEEPEND is a WhaleTimes, Inc. Virtual Research Mission, in cooperation with the DEEPEND Consortium and the Oceanscape Network. For more information visit whaletimes.org

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