DENSITY OF CRISTAE AND DISTRIBUTION OF MITOCHONDRIA IN THE SLOW MUSCLE-FIBERS OF ANTARCTIC FISH

Muscle capillary supply, mitochondrial distribution, and the surface density of mitochondrial cristae have been determined in the pectoral fin adductor profundis muscles of fish that use a labriform mode of locomotion. Species studied were the hemoglobinless Antarctic icefishes Chaenocephalus aceratus and Champsocephalus gunnari, the red-blooded Antarctic fishes Notothenia gibberifrons and Psilodraco breviceps, and the Northern Hemisphere temperate-water fish Callionymus lyra. The volume density of mitochondria in slow-twitch fibers decreased in the order C. gunnari (0.51) > C. aceratus (0.49) > P. breviceps (0.46) > N. gibberifrons (0.25). Surface densities of mitochondrial cristae were lower in C. gunnari (25.2-mu-m2-mu-m-3) and C. aceratus (28.2-mu-m2-mu-3) than in the red-blooded species (32.2-37.0-mu-m2-mu-m-3). This is consistent with the observation that O2 consumption per unit volume of mitochondria is lower in the hemoglobinless species. The density of mitochondria adjacent to capillaries is not significantly different from that in the central core of fibers in C. aceratus. This suggests that slow muscle fibers are not diffusion limited for O2 in species lacking hemoglobin and myoglobin. The high and homogenous distribution of mitochondria in Antarctic fish results in low values for the mean free spacing of mitochondria (1.04-2.96-mu-m) relative to temperature species. This may represent an adaptation to overcome the effects of low temperature on the diffusion of metabolites between capillaries and mitochondria and between mitochondria and myofibrils.