Swordfish Physiology Studies
Heat conservation, vascular specialization and muscle function.
Collaborative researchers:
Diego Bernal, Ph.D. (University of Mass., Dartmouth)
Ashley Stoer, doctoral candidate (UMD)
Jeanine Sepulveda, PhD (MiraCosta College)
Doug Syme, PhD (University of Calgary)
An unexpected result of the trial and testing of Deep-Set Buoy Gear was the unprecedented access it provided to live and healthy swordfish specimens for tagging and physiological studies. As a large predatory fish that is uniquely deep-dwelling, many aspects of the basic biology of swordfish are of particular interest; yet remain poorly understood due to their elusive nature. The markedly low temperatures that swordfish experience at depth demand the use of special adaptations in heat regulation and muscle function, especially in regards to its high functioning predatory nature. PIER researchers are working collaboratively with several laboratories to investigate these aspects of swordfish physiology. Ongoing studies range from examining heat balance and vascular specialization to the effects of temperature on muscle performance.
Thermal Studies
This work uses a suite of laboratory and field techniques to better understand how the swordfish is capable of expanding its thermal niche to waters well below the thermocline. The thermal studies use electronic tags to log the internal body temperature of free swimming swordfish. This specialized tag has a temperature probe that records body temperature at the location of the tag anchor. Once the tag releases from the swordfish, the PIER team sets out to locate and recover it for analysis in the laboratory. Muscle heating and cooling rates are examined over the course of the track period to assess the degree to which swordfish elevate internal muscle temperatures above ambient temperature.
Vascular Specialization
The vascular tissue responsible for circulating blood throughout the body is fixed, stained and sectioned for examination under a microscope. Additional work includes the tracing of the circulation to and from the red muscle to better understand blood flow pathways in swordfish.
Muscle Function
This work brings together a collaborative team of researchers to investigate the effects of temperature on the contractile kinetics, or muscle performance, of swordfish muscle using the work-loop technique. Muscle preparations from freshly caught swordfish are isolated and transported live to the PIER laboratory. Once in the lab, the muscle preparations are cut down in size and mounted to a force transducer in a temperature controlled rig (shown to the right). The live muscle bundle is then subjected to work loop experiments over a series of temperatures (4-24oC). This work assesses how swordfish muscle performs over a range of operating temperatures and forms the basis for doctoral student Ashley Stoer’s dissertation in the Bernal Laboratory at the University of Massachusetts, Dartmouth.
This project compared several aspects of locomotor muscle function and design within a single family of large pelagic sharks, the thresher sharks (Alopiidae). Within the thresher family there are three different species (common thresher, bigeye thresher and pelagic thresher) that all possess an extremely elongate upper caudal lobe, which is as long as their entire body.
