Impact of hypoxia on the metabolism of Greenland halibut (Reinhardtius hippoglossoides)

Greenland halibut (Reinhardtius hippoglossoides), especially juveniles, are frequently found in severely hypoxic areas (18%-25% saturation) of the St. Lawrence Estuary. We investigated the tolerance of this species to hypoxia and evaluated the consequences of low oxygen levels on metabolic capacity. At 5 degrees C, juveniles had a higher critical oxygen threshold than adults (15% versus 11% saturation), indicating that they were less tolerant to hypoxia. Severe hypoxia (19% saturation) did not affect the juveniles' standard metabolic rate but significantly reduced (by 55%) their maximum metabolic rate compared with normoxia. Consequently, the aerobic scope was reduced by 72% in hypoxia compared with normoxia. In juveniles, severe hypoxia increased the duration of digestive processes. The decrease in aerobic scope in hypoxia and the determination of critical oxygen threshold at a saturation level close to actual field dissolved oxygen values strongly suggest that juveniles from the St. Lawrence Estuary are living at the edge of their metabolic capacity. Consequently, the growth and distribution of Greenland halibut could be affected if there are further declines in dissolved oxygen availability.