Energy utilization and metabolism in spawning migrating Early Stuart sockeye salmon (Oncorhynchus nerka): the migratory paradox

Abstract

Sockeye salmon (Oncorhynchus nerka) were followed during their 1400-km-long migration from cessation of feeding outside British Columbia, Canada, up the Fraser River to spawning. Enzymatic capacity (indicative of glycolysis, β-oxidation, and respiratory chain ATP formation), muscle fibre size distribution, body and muscle conformation, and gross chemical composition in different parts of red and white muscle were monitored to determine energy strategies throughout the migration. The mobilization of extramuscular lipid depots was also monitored. The most conspicuous change in white muscle, concomitant with a large decrease in protein content, was an ordered reduction in muscle fibre size and lipid depots with distance covered, resulting in an accumulation of fibres with a cross section between 2000 and 6000 µm2and a maintained level of 4% intramuscular fat. A peak in oxidative capacity was noted in red muscle during the strenuous passage of Fraser Canyon. In white muscle, glycolytic capacity was maintained at least until passage of the Fraser Canyon. Enzymatic capacity was higher in the caudal than rostral part of the muscle. Differences were also found between lateral and dorsal parts of the white muscle, indicating significant differences in the timing and magnitude of enzymatic capacity of red and white muscle.