Seems a Bit Fishy to Me: Specializations for Deep-diving in Swordfish

Session III, Virtual Room 1: BIO: From Dendrites to Dinner

Temperature is one of the most influential factors limiting fish movement patterns. This is because temperature impacts the rates of chemical reactions, which occur in the tissues; and in most fishes, the tissues operate at water temperature. In fact, less than 30 of 30,000 fish species physiologically elevate tissue temperature relative to water temperature (i.e., regional endothermy). Among the large, active, predatory, open-ocean fishes, swordfish (Xiphias gladius) exhibit a unique movement pattern in which they make regular, long duration foraging dives to the cold waters at depth. Swordfish, like tunas and lamnid sharks, possess modifications to their swimming musculature suggestive of regional endothermy. However, past studies were unable to describe in detail the anatomy, which supports regional endothermy, or to document the temperature elevation, which is indicative of regional endothermy. This study combined laboratory and field techniques to better describe the muscular and cardiovascular systems, to measure internal temperatures in free-swimming swordfish, and to investigate the capacity of the muscle to operate at water temperatures experienced by free-swimming swordfish. Ongoing research suggests that swordfish may physiologically slow the rate of muscle cooling during prolonged foraging dives, possibly permitting faster swimming speeds relative to prey or competitors at depth. It is only by understanding how the anatomy and physiology of fishes facilitates the exploitation of different habitats that management can predict the movement patterns of commercially important fishes, like swordfish, in a globally changing ocean.