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Comparative studies of high performance swimming in sharks I. Red muscle morphometrics, vascularization and ultrastructure

D. Bernal^1,*, C. Sepulveda¹, O. Mathieu-Costello² and J. B. Graham¹

¹ Center for Marine Biotechnology and Biomedicine and Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0204, USA
² Department of Medicine University of California San Diego, La Jolla, CA 92093-0623, USA

View larger version (48K): [in a new window]   Fig. 1. Red muscle (RM) distribution patterns in five shark species. Sharks having a more posterior and lateral RM position are (A) blue shark (Prionace glauca) and (B) leopard shark (Triakis semifasciata). Sharks that have a more anterior and central RM position are (C) salmon shark (Lamna ditropis), (D) shortfin mako (Isurus oxyrinchus) and (E) common thresher shark (Alopias vulpinus). The relative amounts of RM in the different positions along the body are expressed as a proportion of the RM cross-sectional area equal to 1 at 50% fork length (see Table 1 for maximum surface area in cm2). Values are means ± S.E.M., except in L. ditropis, where values are means ± range. Half transverse sections of sharks showing the position of the RM (RM digitally enhanced for clarity); broken lines indicate the fork length position of the transverse section. Shark illustrations modified from Goodson (1988), Last and Stevens (1994), Allen (1997) and Tricas et al. (1997), used with permission.

View larger version (14K): [in a new window]   Fig. 2. Scaling of red muscle (RM) mass in five shark species. Shaded symbols represent sharks that have a more anterior and central RM position: salmon shark (squares), shortfin mako (circles; those with a dot in the middle are estimated from Carey et al., 1985) and common thresher (triangles). Unshaded symbols represent sharks that have a more posterior and lateral RM position: blue shark (squares) and leopard shark (diamonds). Species names are given in Table 1. The line defines the allometric relationship between RM mass and body mass for all sharks (r2=0.96, N=30), where TRMM is total red muscle mass (kg) and M is body mass (kg).

View larger version (70K): [in a new window]   Fig. 3. Light micrographs (400x magnification) of mako shark (9.7 kg, 95 cm fork length) red muscle (RM) in longitudinal (A,B) and transverse (C) orientations. The oval in frame A encloses a putative capillary manifold. Some capillaries (c) and fiber bundles (f) are labeled for clarity, and arrows point to some remaining erythrocytes within the capillary lumen.

View larger version (113K): [in a new window]   Fig. 4. Electron micrograph (9208x magnification) of a mako shark (9.7 kg, 95 cm fork length) red muscle (RM) transverse section. Abbreviations: s, subsarcolemma; mf, myofibrils; im, interfibrillar mitochondria; sm, subsarcolemmal mitochondria.