BOLDUC, M.*; BLIER, P.U.; DUTIL, J.-D.: The impact of mitochondial thermal sensitivity on the swimming capacity of Arctic charr

The swimming performance of fish lies on there capacity to convert chemical energy into mechanical energy, trough the contraction of axial muscle. During sustained swimming, ATP required for contraction is mostly supplied by mitochondrial metabolism. Oxygen consumption is thus proportional to work intensity. At low temperature, the aerobic capacities of fish decrease, as well as maximal sustainable swimming speed. However, for many species cold acclimation increases the aerobic capacity of muscle trough an increase of mitochondrial volume-density and/or of mitochondrial enzymes concentration. This compensation suggest that swimming capacities impairment at low temperature is related to a decrease in mitochondrial catalytic capacities. To test this hypothesis, the aerobic scope for activity of Arctic charr (Salvelinus alpinus) was measured at four different temperatures (1, 6, 12 and 18 C). In each fish, mitochondria were extracted from red muscle of one side of the fish. Mitochondrial respiration (pyruvate and malate as substrates) was measured under the same temperatures. Cytochrome c Oxidase activity was assayed in the mitochondrial preparation and in whole red muscle of the other side of the fish. This allowed us to estimate maximal mitochondrial respiration rate in fish red muscle and compare it to aerobic scope for activity under different temperatures.