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.
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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