Characterisation of the swimming muscles of two Subantarctic notothenioids

The histochemical characteristics and distribution of muscle fibre types ha ve been investigated in the swimming muscles of the robalo, Eleginops maclo vinus and the lorcho, Patagonotothen tessellata, Subantarctic notothenioids that inhabit the Beagle Channel. The fibre types were differentiated on th e basis of glycogen and lipid contents and succinate dehydrogenase and myof ibrillar ATPase (mATPase) activities. White, red, intermediate and tonic fi bres were present in the axial muscle of both species. The same fibre types were identified in the pectoral fin adductor muscles, although the interme diate type was absent. The mATPase technique performed at room temperature (21 degrees C) allowed a good differentiation of fibre types. overcoming th e problems found by previous researchers when applying this technique to An tarctic notothenioids. Four different zones (peripheral, mosaic, main and a djacent to the bone) were found in the adductor profundis muscle. The propo rtion of the zones varied along the length of the adductor muscle. For both species, the percentage of red fibres found in the axial muscles was less than 5%, indicating that sustained swimming ability is not dependent on the se muscles. The pectoral muscle mass/carcase mass ratio was significantly g reater in E. maclovinus than in P. tessellata, reflecting a greater capacit y for sustained swimming using pectoral fins.