Swimbladder Retains Gases

a mola mola sunfish with large fins swims in the dark water

Biological Strategy

Ray-finned fishes

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Image: Ilse Reijs and Jan-Noud Hutten / Flickr / CC BY - Creative Commons Attribution alone

Store Gases

Living systems sometimes store gases, such as oxygen, to help maximize respiration or for a variety of other purposes. Gases are often difficult to store because they dissipate and can easily escape. Therefore, most gas storage in living systems can only be temporary. Some examples are fish swim bladders used to control buoyancy, and respiratory sacs in birds that help them maximize access to oxygenated air.

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Modify Buoyancy

Buoyancy is an upward force exerted by air or liquid on a solid object that works against the object’s weight. A hawk glides through air and a duck floats on water due to buoyancy. Some living systems (such as fish eggs) can remain sedentary and therefore maintain the same buoyancy at all times. But most must adjust their buoyancy because they can’t survive long unless they change position. These living systems require strategies to not only be buoyant, but also adjust buoyancy level. They often modify buoyancy by adding or decreasing lift, or by changing their weight. For example, birds like condors that soar for a long time shift the directional orientation of their wingtip feathers to manage buoyancy. Fish alter the amount of air in their swim bladders to increase or decrease their weight, thus altering their buoyancy.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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The gas gland found in the wall of swimbladders in some ray-finned fish keeps gases in the swimbladder from escaping into the blood by passing the blood through an "exchanger."

“But the swimbladder must be filled from dissolved gases in the blood, and it must not lose gas through redissolution into the blood. So secretion of gas from blood into swimbladder faces a big barrier, and swimbladder gas will all too readily go into solution in the fish’s blood and thence out into the ocean. Two devices stand in the way. First, a layer in the swimbladder wall provides a very effective barrier to the passage of oxygen (Lapennas and Schmidt-Nielsen 1977). Second, blood leaving the so-called gas in the wall of the swimbladder passes through an exchanger (fig.5.2) in which blood leaving the swimbladder loses excess dissolved gas specifically to blood moving toward the swimbladder (Scholander 1954).” (Vogel 2003:99-100)

Last Updated September 14, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

Princeton University Press | 17/06/2013 | Steven Vogel

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Reference

Journal article

Secretion of gases against high pressures in the swimbladder of deep sea fishes. 2. The rete mirabile

Scholander, PF

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