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Journal of Experimental Biology 150,205-220 (1990)
Published by Company of Biologists 1990

Ultrastructure of Aerobic Muscle in Antarctic Fishes may Contribute to Maintenance Of Diffusive Fluxes

RICHARD L. LONDRAVILLE ¹ and BRUCE D. SIDELL ¹

¹ University of Maine, Department of Zoology and Center for Marine Studies, Murray Hall, Orono, ME 04469, USA

Quantitative ultrastructural analyses were performed on red (oxidative) and white (glycolytic) skeletal muscles from two species of antarctic fish to identify features of subcellular structure that may be related to muscle metabolism at cold body temperature. Trematomus newnesi (Boulenger) is an active pelagic species and Notothenia gibberifrons (Lönnberg) is a sluggish bottom-dweller. White fibres of both species are poorly vascularized [capillary density, N_A(c,f), for T. newnesi 73.9±11.3mm^-2; for N. gibberifrons is 76.0±14.1mm^-2], and have low percentages of cell volume occupied by mitochondria [volume density, V_v(mit,f), for T. newnesi is 0.014±0.005; for N. gibberifrons is 0.006±0.003]. Ultrastructure of oxidative fibres in both species resembles that of cold-acclimated temperate-zone fishes. Mitochondrial volume densities of red fibres reflect differences in ecotype between species [V_v(mit,f) for T. newnesi is 0.348±0.012; for N. gibberifrons is 0.249±0.007]. The less clustered array of mitochondria in oxidative fibres of T. newnesi compared with N. gibberifrons may support an equivalent flux of aqueous metabolites between mitochondrial and cytoplasmic compartments, despite a greater mean intracellular diffusion distance (_h) between these compartments in T. newnesi than in N. gibberifrons (_h=1.05±0.07µm and 0.77±0.06µm, respectively). Although V_v(mit.)) is higher in red fibres of the active species, capillary supply is less extensive [capillary length density, J_v(c,f), for T. newnesi is 481.3±49.0mm mm^-3; N. gibberifrons is 696.3±33.7mm mm^-3] and the maximal diffusion-distance for oxygen is greater in T. newnesi than in N. gibberifrons (Krogh's radius, R=26.3±1.64µm and 21.5±0.51µm, respectively). A mismatch appears to exist between oxygen supply [J_v(c,f)] and oxygen demand [V_v(mit,f)] in T. newnesi red fibres in view of published data for other fishes. The twofold higher volume density of lipid [V_v(lip,f)] in T. newnesi compared with N. gibberifrons may resolve this paradox [V_v(lip,f) is 0.026±0.002 and 0.012±0.004, respectively]. Because oxygen is at least four times more soluble in lipid than in aqueous cytoplasm, lipid may enhance oxygen flux through oxidative muscle and play a role similar to myoglobin in these myoglobin-poor fishes.

Key words: ultrastructure, diffusion, antarctic fish, aerobic muscle, stereology

Accepted on January 24, 1990

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