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In the Estuary and Gulf of St. Lawrence, northern shrimp (Pandalus borealis) and Greenland halibut (Reinhardtius hippoglossoides) are usually found at depths > 150 m and thus frequently inhabit hypoxic areas (18–50% saturation). The impact of a one-week exposure to different levels of dissolved oxygen (100, 40, 30, and 20% saturation) at 5 °C was evaluated in adult shrimp and juvenile Greenland halibut; the effect of acute exposure to severe hypoxia was also assessed in Greenland halibut. The activities of key enzymes involved in aerobic (citrate synthase [CS], cytochrome c oxidase [COX]) and anaerobic (pyruvate kinase [PK], phosphoenolpyruvate carboxykinase [PEPCK], lactate dehydrogenase [LDH]) pathways, and of enzymes involved in antioxidant defence (superoxide dismutase, glutathione peroxidase [GPx], and catalase [CAT]) were measured. Quantitative real-time PCR analysis was also performed in Greenland halibut. In northern shrimp exposed to chronic hypoxia, muscle CS activity decreased by ~ 40%. Muscle LDH activity was significantly reduced, with a more intense reduction in males. At the same time, hepatopancreas GPx activity increased under hypoxia, and this response was stronger in males. Overall, the results suggest the presence of a threshold above 40% saturation and higher hypoxia tolerance in males. In juvenile Greenland halibut, exposure to chronic hypoxia elicited a more wide-ranging enzymatic response than did acute exposure to severe hypoxia. Under chronic hypoxia, CS activity decreased and PK and LDH activity were respectively 46% and 57% lower than in normoxia. There were no major changes in the activity of antioxidant enzymes, but activity in normoxia was high compared to other fish species. Interestingly, the relative expression of genes coding for muscle COX (severe hypoxia), liver PEPCK (chronic), and CAT (chronic) activities were triggered in hypoxia. The absence of a corresponding change in enzyme activity makes the interpretation of these result

In the Estuary and Gulf of St. Lawrence, northern shrimp (Pandalus borealis) and Greenland halibut (Reinhardtius hippoglossoides) are usually found at depths > 150 m and thus frequently inhabit hypoxic areas (18–50% saturation). The impact of a one-week exposure to different levels of dissolved oxygen (100, 40, 30, and 20% saturation) at 5 °C was evaluated in adult shrimp and juvenile Greenland halibut; the effect of acute exposure to severe hypoxia was also assessed in Greenland halibut. The activities of key enzymes involved in aerobic (citrate synthase [CS], cytochrome c oxidase [COX]) and anaerobic (pyruvate kinase [PK], phosphoenolpyruvate carboxykinase [PEPCK], lactate dehydrogenase [LDH]) pathways, and of enzymes involved in antioxidant defence (superoxide dismutase, glutathione peroxidase [GPx], and catalase [CAT]) were measured. Quantitative real-time PCR analysis was also performed in Greenland halibut. In northern shrimp exposed to chronic hypoxia, muscle CS activity decreased by ~ 40%. Muscle LDH activity was significantly reduced, with a more intense reduction in males. At the same time, hepatopancreas GPx activity increased under hypoxia, and this response was stronger in males. Overall, the results suggest the presence of a threshold above 40% saturation and higher hypoxia tolerance in males. In juvenile Greenland halibut, exposure to chronic hypoxia elicited a more wide-ranging enzymatic response than did acute exposure to severe hypoxia. Under chronic hypoxia, CS activity decreased and PK and LDH activity were respectively 46% and 57% lower than in normoxia. There were no major changes in the activity of antioxidant enzymes, but activity in normoxia was high compared to other fish species. Interestingly, the relative expression of genes coding for muscle COX (severe hypoxia), liver PEPCK (chronic), and CAT (chronic) activities were triggered in hypoxia. The absence of a corresponding change in enzyme activity makes the interpretation of these result

Growth of Pandalus borealis post-larval stages was measured in relation to size and temperature. Growth characteristics, including intermolt period (IP), molt increment (MI) in size and mass, and tissue allocation in juvenile, male, and female shrimp, were evaluated at 2, 5, and 8°C, the temperature range where this species is generally found in the Northwest Atlantic. Significant variations in growth were associated with temperature and shrimp size. IP (days) increased significantly with shrimp size and was inversely related to temperature. Size (cephalothorax length in mm) and temperature effects were best described by IP = 10(0.67 log(CL) − 0.06 T − 1.34). The pronounced effect of temperature on IP while MIS changed little indicated that the main influence of temperature on growth rate of P. borealis was through IP. Specific growth rate (SGRS) decreased rapidly with size to near zero values in females. Overall, juveniles were much more sensitive to temperature variations than adults, suggesting that temperatures encountered during the juvenile stage will largely influence the growth trajectory of the population. -- Keywords : Molt Cycle ; Size Increment ; Shrimp Population ; Juvenile Shrimp ; Intermolt Period.

Growth of Pandalus borealis post-larval stages was measured in relation to size and temperature. Growth characteristics, including intermolt period (IP), molt increment (MI) in size and mass, and tissue allocation in juvenile, male, and female shrimp, were evaluated at 2, 5, and 8°C, the temperature range where this species is generally found in the Northwest Atlantic. Significant variations in growth were associated with temperature and shrimp size. IP (days) increased significantly with shrimp size and was inversely related to temperature. Size (cephalothorax length in mm) and temperature effects were best described by IP = 10(0.67 log(CL) − 0.06 T − 1.34). The pronounced effect of temperature on IP while MIS changed little indicated that the main influence of temperature on growth rate of P. borealis was through IP. Specific growth rate (SGRS) decreased rapidly with size to near zero values in females. Overall, juveniles were much more sensitive to temperature variations than adults, suggesting that temperatures encountered during the juvenile stage will largely influence the growth trajectory of the population. -- Keywords : Molt Cycle ; Size Increment ; Shrimp Population ; Juvenile Shrimp ; Intermolt Period.

PANDALUS borealis Kröyer est une crevette hermaphrodite protérandrique. A la suite d'un stade larvaire pélagique, la crevette prend la forme adulte. La première maturité sexuelle de l'animal se réalise normalement sous la forme mâle. L'ovotestis produit alors des spermatozoïdes. Cependant, la glande produit aussi des ovocytes qui n'entrent pas en vitellogénèse, donc ne maturent pas. Ce processus se fait sous le contrôle d'hormones, dont notamment celle produite par la glande androgène placée à la base du canal déférent, près de l'ampoule terminale. Les crevettes mâles vont par la suite changer de sexe après un certain nombre d'années (Jusqu'à environ cinq années) selon les milieux surtout en relation avec la température ambiante. Dès lors, il n'y a plus de formation de spermatozoïdes et la glande, devenue un ovaire fonctionnel, produit des oeufs. Un échantillonnage fait dans le golfe Saint-Laurent nous a permis de mieux comprendre certaines composantes biologiques de cette espèce. De plus nous avons pu, par l'analyse des données biotiques recueillies, étudier certaines relations entre divers paramètres. Enfin, grâce aux techniques histologiques, nous avons pu étudier l'organisation et les modifications du système reproducteur des crevettes mâles et de celles en voie de devenir des femelles. Il existe une relation linéaire entre la longueur et la masse de la crevette, et ce pour tous les stades étudiés. De plus, le patron de croissance des crevettes de l'échantillonnage est du même type que celui qu'on trouve dans le golfe du Maine. Ainsi, la crevette augmente sa taille continuellement tout au long de sa vie, mais le taux d'accroissement de la taille diminue avec l'âge de l'animal. Les gonades mâles et celles des femelles en repos ovarien sont petites par rapport à la masse de la crevette. Celles des crevettes dont les oeufs sont en maturation ont une masse qui augmente avec la taille des individus, mais qui semble atteindre un plateau car l'indice gonosomatique des