MARTINEZ, M. L.; GUDERLEY, H. E.; DUTIL, J.-D.; University of New Orleans, Lousiana; Universit� Laval, Qu�bec, Canada; Institut Maurice-Lamontagne, Qu�bec, Canada: Metabolic Correlates of Sprint Swimming by Cod, Gadus morhua

This study examined whether sprint swimming performance of Atlantic cod is determined by their physiological condition, and assessed whether muscle metabolic capacities can explain such links. After 12 weeks of feeding or starvation, marked differences were observed in the Fulton’s condition factor: 0.5 � 0.4 (starved) and 1.0 � 0.09 (fed). In white muscle, we measured four glycolytic enzymes: (PFK, PK, CK and LDH), two mitochondrial enzymes, (CCO and CS), the biosynthetic enzyme (NDPK), water and total protein contents and total white muscle mass. Muscle samples were taken at three positions along the length of the fish. The sprint performance of cod expressed as absolute speed (cm s-1) or relative speed (body length, bl s-1) was significantly affected by the feeding regime. Of all variables included in the analysis, the activity of CCO and NDPK in white muscle behind the head were the primary determinants of the sprint performance expressed as absolute speed (cm s-1). When we expressed the sprint swimming as relative speed (bl s-1), the activity of CCO in white muscle behind the head was the only determinant of sprint performance. Although the statistical relationship changed somewhat depending on how we express the speed, it is clear that the activity of CCO in white muscle sampled behind the head is the most important variable linked with sprint performance of cod. Our results suggest that even though white muscle has a lower mitochondria volume density than red muscle, an increase in the mitochondrial volume density in white fibres may reduce the severity of temporal and spatial gradients in [PCr] and ATP before exercise. In this fashion, a higher oxidative capacity in white muscle of fed cod could increase their sprint swimming performance.