Meeting Abstract
Swordfish (Xiphias gladius) are unique among pelagic fish in their ability to undergo extensive dives characterized by rapid (minutes) and large (>18°C) changes in ambient temperature. Relative to other billfish, swordfish, possess anatomical traits [e.g., medial position of the aerobic red swimming muscles (RM), lateral blood vessels] that may allow for the retention of metabolic heat (regional endothermy) in the RM. However, to date there have been no studies detailing the presence of vascular specializations that may support RM endothermy and if swordfish are capable of altering rates of while body heat transfer during their dives. The objectives of this study were to (1) describe the vascular layout perfusing the RM, (2) measure water and body temperature in free-swimming swordfish, (3) and develop Newtonian and Fourier heat transfer models to elucidate potential physiological mechanisms governing RM endothermy or thermoregulation in free-swimming swordfish. Gross dissections and histological techniques revealed the presence of central retia as well as laterally positioned, closely opposed arteries and veins that may form rudimentary RM-associated heat exchanging retia. In addition, body temperature data and models suggest that manipulation of blood flow through retia of differential heat retention efficiency could describe the changes in whole-body heat transfer observed in free-swimming swordfish. Taken together, swordfish appear to possess anatomical specializations that permit physiological control of heat transfer, allowing swordfish to regularly exploit disparate thermal environments while maintaining a somewhat steady RM operating temperature.
