Functional Morphology of Y-Bones in Esocid Fishes

Functional Morphology of Y-Bones in Esocid Fishes Michael Rush & Takashi Maie, Ph.D. Abstract Intermuscular bones, commonly referred to as Y bones or pin bones, are ossified segments of ligaments found in the myosepta of most teleost fishes. These bones are attached to the vertebrae in two locations between neural arches and centra, and thus, form a forked (y-shaped) configuration. Esocid species (pickerel and pike) have sets of well-ossified intermuscular bones along their vertebral columns. In this study, we examined grass pickerel (Esox americanus vermiculatus) and northern pike (E. lucius) that are known to present a difference in the y-bone arrangement using a series of dissections and the clear-and-staining technique. Both E. americanus vermiculatus and E. lucius are freshwater fish, commonly found in clear, slow flowing waters with thick vegetation. E. lucius grow much larger than E. americanus vermiculatus and are apex predators, while E. americanus vermiculatus are lower predators in the ecosystem. We discuss the functional implications of how these intermuscular bones are arranged in relation to ecology and behavior of these esocid species. Our experimental results provide insight into function and evolution of intermuscular bones in teleosts