Northern shrimp ( Pandalus borealis ) oxygen consumption and metabolic enzyme activities are severely constrained by hypoxia in the Estuary and Gulf of St. Lawrence

Northern shrimp is an important commercial species in the Estuary and Gulf of St. Lawrence. It is usually found at depths >150m and thus frequently inhabits hypoxic areas (18–40% saturation) in this region. To evaluate the impact of hypoxia on adult shrimp, males and females were exposed to different levels of dissolved oxygen at two temperatures (5 and 8°C). Standard and maximal metabolic rates as well as the critical oxygen threshold were measured. In addition, metabolic and antioxidant enzyme activities were measured at 5°C. Females had a higher critical oxygen threshold than males at both temperatures (15.5 and 22.2 vs. 9.0 and 13.8 at 5 and 8°C respectively), indicating that they were less tolerant of hypoxia. A decrease in glycolytic and fermentation enzyme activities confirmed this result: in females, severe hypoxia significantly decreased the specific activities of citrate synthase and of enzymes involved in anaerobic biochemical pathways (lactate dehydrogenase, pyruvate kinase, and phosphoenolpyruvate carboxykinase (PEPCK)); in males, only the PEPCK activity decreased significantly while glutathione peroxidase (antioxidant defense) activity increased significantly. In females, severe hypoxia (22% sat.) did not affect the standard metabolic rate but significantly reduced (by ~43%) the maximum metabolic rate compared to normoxia. Consequently, aerobic scope was reduced by ~58% at 22% sat. compared to normoxia. This suggests that the shrimp's flexibility to respond to metabolic demands, including such activities as vertical migration, foraging, and egg production, could be reduced in hypoxic conditions, especially in females.