TENDON STRUCTURE OF THE CAUDAL FIN IN THE BLUE SHARK, PRIONACE-GLAUCA

A qualitative description of the myology of three blue shark (Prionace glauca) caudal fins is presented, forming the basis for a quantitative analysis of the tendon structure. The primary musculature consists of dorsal epaxial and ventral hypaxial portions. The average crimp angle of collagen fibres in the epaxial tendons (14.1-26-8-degrees) is significantly greater (P<0.01) than that in the hypaxial tendons (1.8-14.5-degrees). Similarly, epaxial tendons exhibit a significantly lower fibrocyte nuclear density (0.02-0.03 nuclei-mu-m-2) than do the corresponding hypaxial tendons (0.05-0.08 nuclei-mu-M-2) (p < 0.01). The greater crimp angle and lower fibrocyte nuclear density in epaxial tendons indicate increased tensile strength, consistent with the comparatively greater muscular force required to move the upper caudal lobe.