Meeting Abstract
Hyperostosis, extra bone growth, has evolved independently in at least 22 families of fishes most of which are tropical or subtropical marine species. While the presence of hyperostosis is well documented in fishes, the mechanism driving the development of the extra bone growth is unclear. We documented hyperostosis along the dorsal pterygiophores in Oarfish, Regalecus russelii. This is the second lamrpiform fish with hyperostosis and the first case documented in a truly mesopelagic, temperate zoned fish. In oarfish, the majority of the dorsal pterygiophores are highly unmineralized, acellular bones that shift to stiffened, cellular, hyperostotic growths near the distal edge. Oarfish lack a swim bladder so they must continuously beat their bi-directional dorsal fin to maintain position within the water column and while engaged in locomotory behavior. It is therefore not surprising that these fishes have areas of localized, hyperostotic skeletal elements along the dorsal pterygiophores that, presumably, function as a stiffened lever system to support fin undulation. We noted that hyperossification was not present in all fish examined and was only documented in fishes with total lengths greater than 3 m.
