NYACK, A.C.*; KINSEY, S.T.; University of North Carolina, Wilmington: Changes in mitochondrial distribution and fiber diameter during ontogeny in black sea bass (Centropristis striata) white muscle and potential influence on aerobic metabolism

In some fishes that undergo large developmental increases in body mass, hypertrophic growth can yield white muscle fibers that are very large in diameter. This should not affect the burst contraction function of these fibers, however, aerobic post-contractile processes may be limited by the low fiber SA:V and large intracellular diffusion distances associated with increased fiber size. We have previously found that during growth in crustaceans some burst muscle fibers undergo extreme hypertrophy, and the increase in fiber size is associated with a dramatic shift in the distribution of mitochondria to the periphery of the fiber. To determine if this metabolic reorganization is more widespread, this study examined the white muscle fiber diameter, mitochondrial fractional volume, and mitochondrial distribution in black sea bass (C. striata) that ranged in body mass from 2 � 4500 g. The white muscle fiber diameters in C. striata ranged from 8.2 �m in juveniles to 440.1 �m in adults. Intermyofibrillar mitochondria fractional volume was found to be similar in juvenile and adult fishes (< 0.01). However, as in crustacean muscle, a significant increase in the fractional volume of sub-sarcolemmal mitochondria occurred during ontogeny. Thus, it appears that this developmental reorganization of mitochondria is a general feature of fibers that undergo large increases in size. Increases in mitochondria fractional volume at the sarcolemmal membrane may be important to counteract the effects that decreased fiber SA:V potentially has on aerobic processes, such as post contractile metabolic recovery.