GRAY, P.*; MEYERS, R.; BERNAL, D.; Weber State University; Weber State University; University of Massachusetts, Dartmouth: The effect of temperature on the metabolic biochemical capacity in the hearts of warm bodied sharks
In most sharks the temperature of the locomotor and cardiac tissues is in similar to that of the ambient water and changes (i.e., cools) as they migrate to higher latitudes or dive to cooler waters, thus decreasing the tissue�s overall metabolic activity. The temperature of the heart in lamnid and thresher sharks is also similar that of other shark (i.e., equal to ambient) but these sharks differ by maintaining an above ambient body temperature (i.e., they are warm bodied). The present study compared the metabolic biochemical activities of myocardial tissue between lamnids, thresher and other sharks without the warm bodied condition. The maximal enzymatic activities of citrate synthase (CS, aerobic index) and lactate dehydrogenase (LDH, anaerobic index) were measured from 5 to 30�C to determine thermal effects. Gross cardiac morphology was then used in combination with the metabolic indices to determine if anatomical and biochemical specializations, unique to warm bodied sharks, are present. Preliminary findings show that the heart of lamnids has an increased CS activity but a similar thermal effect relative to other sharks. By contrast, the CS activity for the thresher is similar to that of other non-lamind sharks. All shark species had a both similar LDH activity and thermal effect. Cardiac morphology in lamnids showed an increased relative mass and fiber geometry suggestive of an enhanced contractile capacity. In summary, warm bodied sharks have similar thermal sensitivities when compared to other sharks, but have an overall higher aerobic capacity relative when compared at the same temperature. Thus, the hearts of warm bodied sharks have thermal effects that are not unlike those of other sharks, but are relatively larger and have a fiber geometry suggesting an improved contractile capacity relative to other sharks.
