Osmorespiratory Compromise in an Elasmobranch: Oxygen Consumption, Ventilation and Nitrogen Metabolism in Dogfish Sharks (squalus Suckleyi) Exposed to Hypoxia in Different Salinities.

Fish face a functional trade-off at the gills between minimizing ion movement and maximizing oxygen uptake – the osmorespiratory compromise, but the extent of this trade-off remains poorly understood in elasmobranchs. Using the Pacific dogfish shark, we assessed the impacts of progressive hypoxia in animals acclimated to 25, 30 and 36 ppt for 4 days at 12 °C. Plasma osmolality increased with water osmolality at 36 ppt (osmoconformation) and decreased at 25 ppt. Plasma urea decreased at 25 ppt, though to a lesser extent than plasma Cl−, while plasma urea increased to a greater extent than plasma Cl− at 36 ppt. In normoxia, oxygen consumption rate (MO2) was elevated by 60