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Journal of Experimental Biology 163,97-118 (1992)
Published by Company of Biologists 1992

PHYSIOLOGICAL RESPONSE OF THE ATLANTIC COD (GADUS MORHUA) TO HYPOXIA AT VARIOUS ENVIRONMENTAL SALINITIES

GUY CLAIREAUX ¹ and JEAN-DENIS DUTIL ²

¹ Insdtut Maurice Lamontagne Ministère des Pêches et des Océans, 850, route de la mer, Mont-Joli (Québec), Canada G5H 3Z4; Present address: Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1
² Insdtut Maurice Lamontagne Ministère des Pêches et des Océans, 850, route de la mer, Mont-Joli (Québec), Canada G5H 3Z4

Atlantic cod (Gadus morhua L.) acclimated to water salinities ranging from 28 to 7 were exposed to mild (8.0 kPa) or severe (4.0 kPa) hypoxic conditions for 6h. In each experiment, respiratory, acid-base, ionic, haematological and metabolic disturbances were analyzed. During mild hypoxia, a strong hyperventilatory response was observed, resulting in a respiratory alkalosis that persisted throughout the 6-h trial. Plasma Cl^- and pyruvate levels were the only other variables to display significant changes: they both increased. In more severe hypoxic conditions, although the ventilatory response was the same, a weak metabolic acidosis was superimposed. The haematological response (increased haematocrit and decreased mean cellular haemoglobin content) suggested that catecholamines were released into the blood. Both Na⁺ and Cl^- concentrations increased significantly. Metabolic perturbations occurred: plasma lactate, pyruvate and glucose concentrations increased markedly. Though lactate concentrations in liver, heart and white muscle increased, the concentrations of pyruvate, glucose and glycogen did not change significantly. Water salinity affected the amplitude of the ionic responses during hypoxia: the amplitude decreased with decreasing salinity. Irrespective of water salinity, 23 of 29 fish survived the severe hypoxic conditions. This relatively good tolerance of low water oxygenation, as compared with other marine bottom-feeders, suggests that this species may face poorly oxygenated waters in the wild. Together with temperature and salinity, ater oxygen content may thus be an important variable to take into account in the study of the distribution and migration patterns of Atlantic cod.

Key words: Atlantic cod, Gadus morhua, hypoxia, water salinity

Accepted on October 16, 1991

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