Bernal, D.*; Dickson, K.; Graham, J.: Convergence for high performance swimming in lamnidsharks and tunas. Thermoregulation and metabolic biochemistry.

This study documents the shortfin mako shark’s (Isurus oxyrinchus) capacity to thermoregulate and the thermal effects on metabolic enzymes activities and compares the results to tunas. Elasmobranchs and bony fishes have evolved independently for more than 400 million years. However, two Recent groups, the lamnid sharks and tunas, display remarkable similarities in features related to swimming performance. Traits separating these two groups from other fishes include a higher degree of body streamlining, a shift in position of the aerobic locomotor muscle (red muscle, RM) that powers sustained swimming to an anterior position in the body and to near to the vertebral column, an increased gill surface area, a higher blood oxygen carrying capacity, the capacity to conserve metabolic heat (i.e., endothermy), and greater muscle aerobic and anaerobic enzyme activities at in vivo temperatures. The suite of morphological, physiological, and biochemical specializations that define “high-performance fishes” have been extensively characterized in the tunas. This study uses the convergent features of lamnids and tunas in order to gain insight into the extent that comparable environmental selection pressures have led to the independent origin of similar suites of functional characteristics in distinctly different taxa. This study tests the hypothesis that, despite differences between teleost and elasmobranch fishes, lamnids and tunas, have evolved morphological and physiological specializations that enhance their swimming performance relative to other sharks and most other high performance pelagic fishes.