Review: Analysis of the evolutionary convergence for high performance swimming in lamnid sharks and tunas

Elasmobranchs and bony fishes have evolved independently for more than 400 million years. However, two Recent groups, the lamnid sharks (Family Lamnid ae) and tunas (Family Scombridae), display remarkable similarities in featu res related to swimming performance. Traits separating these two groups fro m other fishes include a higher degree of body streamlining, a shift in the position of the aerobic, red, locomotor muscle that powers sustained swimm ing to a more anterior location in the body and nearer to the vertebral col umn, the capacity to conserve metabolic heat (i.e. regional endothermy), an increased gill surface area with a decreased blood-water barrier thickness , a higher maximum blood oxygen carrying capacity, and greater muscle aerob ic and anaerobic enzyme activities at in vivo temperatures. The suite of mo rphological, physiological, and biochemical specializations that define 'hi gh-performance fishes' have been extensively characterized in the tunas. Th is review examines the convergent features of lamnid sharks and tunas in or der to gain insight into the extent that comparable environmental selection pressures have led to the independent origin of similar suites of function al characteristics in these two distinctly different taxa. We propose that, despite differences between teleost and elasmobranch fishes, lamnid sharks and tunas have evolved morphological and physiological specializations tha t enhance their swimming performance relative to other sharks and most othe r high performance pelagic fishes. (C) 2001 Elsevier Science Inc. All right s reserved.