Francois Barthelat, CC BY-ND
Fish fins are not simple membranes that fish flap right and left for propulsion. They probably represent one of the most elegant ways to interact with water. Fins are flexible enough to morph into a wide variety of shapes, yet they are stiff enough to push water without collapsing.
The secret is in the structure: Most fish have rays—long, bony spikes that stiffen the thin membranes of collagen that make up their fins. Each of these rays is made of two stiff rows of small bone segments surrounding a softer inner layer. Biologists have long known that fish can change the shape of their fins using muscles and tendons that push or pull on the base of each ray, but very little research has been done looking specifically at the mechanical benefits of the segmented structure.
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Source : fastcompany.com
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