Fins Allow Bidirectional Movement

Biological Strategy

African freshwater electric eel

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Move in/on Liquids

Water is not only the most abundant liquid on earth, but it’s vital to life–so it’s no surprise that the majority of life has evolved to thrive on and under its surface. Moving efficiently in and on this dense and dynamic substance presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag, utilize surface tension, fine tune buoyancy, and take advantage of various types of currents and fluid dynamics. For example, sharks can slide through water by reducing drag due to their streamlined shape and specially shaped features on their skin.

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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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Undulations of the tail and dorsal fins of the African freshwater electric eel allow for smooth bidirectional movement through the water.

Image: Student of Marjan Eggermont at University of Calgary Schulich School of Engineering /

Image: Wiki-Harfus / CC BY SA - Creative Commons Attribution + ShareAlike

“In addition to forward undulatory swimming, Gymnarchus niloticus can swim via undulations of the dorsal fin while the body axis remains straight; furthermore, it swims forward and backward in a similar way, which indicates that the undulation of the dorsal fin can simultaneously provide bidirectional propulsive and maneuvering forces with the help of the tail fin.” (Li et al. 2005:115)

Last Updated June 6, 2018

References

Journal article

Locomotion of Gymnarchus niloticus : Experiment and kinematics

Fei Li, Tian-jiang, H; Fei, L; Guang-ming, W; Lin-cheng, S.

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