Meeting Abstract

P1.66  Sunday, Jan. 4  The effect of temperature on the muscle contractile properties in the common thresher shark BERNAL, Diego*; SYME, Douglas; MCGILLIVRAY, David; DONLEY, Jeanine; SEPULVEDA, Chugey; Univ. Mass. Dartmouth; Univ. Calgary; Univ. Calgary; MiraCosta College; Pfleger Institute of Environmental Research dbernal@umassd.edu

This project measured the contractile properties of the aerobic red (RM) and anaerobic white myotomal (WM) muscle in the common thresher shark (Alopias vulpinus) captured in the Southern California Bight. Muscle twitch kinetics were measured in situ with a portable stimulator and force transducer and showed no significant longitudinal variation in twitch response of superficial WM. Laboratory preparations of WM fibers exhibited isometric twitches at temperatures as low as 8C, while RM twitches drastically slowed (time to peak force in excess of 1.5s) at this temperature. The in vitro work loop technique was used to quantify temperature dependent work and power output in isolated muscle preparations. In WM the cycle frequency yielding maximum power ranged from 1.0Hz at 8C to 1.5Hz at 24C, and positive power was maintained up to 2.5Hz at 8C and 4.0Hz at 24C. In the RM positive power output was restricted to relatively lower frequencies, less than 1.5Hz at 24C, less than 1.0Hz at 16C, and 0.5Hz at 8C. These results show that while thresher shark WM can power fast swimming across a wide range of temperatures, the RM is more limited in its thermal tolerance. However, the overall thermal effect on RM power in the common thresher appears to not be as pronounced as that documented in other regionally endothermic sharks.