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Why do oarfish swim vertically?
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Illustration of an oarfish (Regalecus glesne) with a long, ribbon-like blue body, red dorsal fin, and trailing fin rays, shown with scale bars for 1 meter and 3 feet to indicate its large size.
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Illustration of an oarfish (Regalecus glesne) with a long, ribbon-like blue body, red dorsal fin, and trailing fin rays, shown with scale bars for 1 meter and 3 feet to indicate its large size.
Oarfish The Regalecus glesne, commonly called oarfish, has a silver, ribbonlike body with a long red dorsal (back) fin that rises as a manelike crest on top of the head.

Why do oarfish swim vertically?

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Oarfish swim vertically to camouflage themselves in their deep-water habitat. This orientation hides their flattened bodies from predators above, and their reflective silver flesh blends into the color of the water around them in the low light of the depths.

Swimming vertically also has other advantages. It helps oarfish spot their prey—small fish and plankton—more easily against the light coming in from above them while staying relatively still. Oarfish, with their elongated, light bodies are also easily carried away by currents. A vertical orientation allows them to leverage their large back fin to navigate more easily and conserve energy in a habitat low on nutritional resources.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Aman Kumar.