LATITUDINAL VARIATION IN THE ABUNDANCE AND OXIDATIVE CAPACITIES OF MUSCLE MITOCHONDRIA IN PERCIFORM FISHES

The abundance, distribution and oxidative capacities of mitochondria h ave been investigated in the red pectoral fin adductor muscles of fish (Order Perciformes) that use a predominantly labriform style of swimm ing, Mediterranean Sea species from the families Labridae, Serranidae, Sparidae and Antarctic Nototheniidae and non-Antarctic Nototheniidae and Channichthyidae were studied, Sub-Antarctic species from the Beagl e Channel, Tierra del Fuego, included the pelagic haemoglobin-less ice fish (Champsocephalus esox) and the robalo (Eleginops maclovinus), whi ch occurs as far north as 35 degrees S. In Champsocephalus esox, the m itochondrial volume density of red muscle was 0.51 and mitochondrial c ristae surface density (43.9 mu m(2) mu m(-3)) was higher than reporte d for Antarctic icefishes, In the red-blooded, active pelagic or semi- pelagic species, mitochondrial volume density was within the range 0.2 7-0.33 regardless of habitat temperature, Amongst less active demersal species, mitochondrial volume density ranged from 0.29-0.33 in polar species to 0.08-0.13 in Mediterranean species, In Antarctic species an d Champsocephalus esox, myofibrils occurred in ribbons or clusters one fibril thick entirely surrounded by mitochondria, The volume density of intracellular lipid droplets was not correlated with activity patte rns or habitat temperature, In a comparison of Eleginops maclovinus ca ught in summer (approximately 10 degrees C) and winter (approximately 4 degrees C), mitochondrial volume density did not differ, whereas the surface density of mitochondrial clusters was higher in summer fish, The temperature-dependence of the state 3 respiration rate of isolated mitochondria with pyruvate as substrate was described by a single qua dratic relationship for all species, indicating no significant up-regu lation of the maximum rate of oxygen uptake per milligram mitochondria l protein in Antarctic species, Our results support the conclusion tha t increasing the volume and surface density of mitochondrial clusters is the primary mechanism for enhancing the aerobic capacity of muscle in cold-water fish.