ORIGINAL PAPER Sex differences in circulatory oxygen transport parameters of sockeye salmon (Oncorhynchus nerka) on the spawning ground

Abstract Upon reaching sexual maturity, several species of male salmonids possess a relative ventricular mass (rMV) that may be up to 90 % larger than females. This can increase maximum cardiac stroke volume and power out-put, which may be beneficial to increasing the oxygen transport capacity of male salmonids during the spawning period. It may be further hypothesized, therefore, that other variables within the circulatory oxygen transport cascade, such as blood oxygen-carrying capacity and heart rate, are similarly enhanced in reproductively mature male salmo-nids. To test this idea, the present study measured a range of circulatory oxygen transport variables in wild male and female sockeye salmon (Oncorhynchus nerka) during their spawning period, following a 150 km migration from the ocean. The rMV of male fish was 13 % greater than females