Rotational Feeding: Overcoming Gape-Limited Foraging in Anguillid Eels

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Abstract
The American eel, Anguilla rostrata, feeds in part by grasping food and spinning about its long axis, thereby tearing pieces from large prey items. Eels spin when feeding on prey that is too large to be swallowed whole or that cannot be torn by jerking or shaking. A spinning bout involves initial grasp, twist, spin and withdraw. Spinning is induced when food width is ≥ 85% of external jaw width; firm foods are more likely to induce spinning than are easily degraded items. Videotape analysis indicated spinning rates as high as 14.3 rotations/sec (x̄ = 6.1). Large (400-600 mm) eels rotated at slightly slower rates than small (150-210 mm) eels. Spinning enables eels and other elongate aquatic vertebrates to tear apart prey too large to be swallowed whole, despite a lack of specialized cutting dentition. Spinning thus reduces constraints of gape limitation that characterize foraging in many predaceous fishes. Ecological, physiological, functional morphological and phylogenetic aspects of rotational feeding in anguillid eels and other eel-like animals remain largely unstudied.

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