Function of Hyperostoses in the Pterygiophores of Oarfish (Regalecus Russelii)

Overview

The oarfish (Regalecus russelii) swims via undulation of its dorsal fin with no additional thrust contributed through anguilliform locomotion. Fish greater than 3 meters have distinctive hyperostoses, excessive mineralized bone growths, along their dorsal pterygiophores. Why then do large oarfish consistently develop these hyper-mineralized, structures embedded in poorly mineralized bones? We hypothesize that the hyperostossified components provide a rigid surface for supporting dorsal fin oscillation. We modeled the pterygiophores as beams with a spherical “hyperostosis” embedded within the bone. The spheres were added in one of 3 locations along the bone: 1) at the distal end of the beam, 2) in the center of the beam, and 3) between the center and the distal end of the beam. This allowed us to test whether the position of the hyperostosis affected the strength of the pterygiophore. The models were 3D printed first with resin, to test whether the structural properties of a beam are affected by the addition of hyperostoses and next using calcium carbonate (to imitate bone) to test whether the material of the beam contributes to the overall integrity of the beam. Both models were tested as cantilevered beam tests using an Instron 5942 materials tester. We found that for both tests, the beams broke prior to failure at the hyperostoses. Our findings suggest that the hyperostoses function as increased support for the pterygiophore and are likely the connection point for the uppermost horizontal septa musculature as well as the protractor and retractor muscles that control the dorsal fin.

Competition history

• AJAS 2020 Category not listed

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