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Title: Respiratory responses to progressive hypoxia in the Amazonian oscar, Astronotus ocellatus
Authors: Scott, Graham R.
Wood, Chris M.
Sloman, Katherine A.
Iftikar, Fathima I.
Boeck, Gudrun de
Val, Vera Maria Fonseca Almeida e
Val, Adalberto Luis
Keywords: Animals Experiment
Cell Respiration
Controlled Study
Gas Exchange
Oxygen Consumption
Priority Journal
Adaptation, Physiological
Anaerobic Threshold
Cell Respiration
Energy Metabolism
Lactic Acid
Oxygen Consumption
Respiratory Mechanics
Issue Date: 2008
metadata.dc.publisher.journal: Respiratory Physiology and Neurobiology
metadata.dc.relation.ispartof: Volume 162, Número 2, Pags. 109-116
Abstract: This study determined the respiratory responses to progressive hypoxia in oscar, an extremely hypoxia-tolerant Amazonian cichlid. Oscar depressed oxygen consumption rates (over(M, ̇)O2), beginning at a critical O2 tension (Pcrit) of 46 Torr, to only 14% of normoxic rates at 10 Torr. Total ventilation (over(V, ̇)w) increased up to 4-fold, entirely due to a rise in ventilatory stroke volume (no change in ventilatory frequency), and water convection requirement (over(V, ̇)w / over(M, ̇)O2) increased substantially (up to 15-fold). Gill O2 extraction fell steadily, from 60% down to 40%. Although O2 transfer factor (an index of gill O2 diffusion capacity) increased transiently in moderate hypoxia, it decreased at 10 Torr, which may have caused the increased expired-arterial PO2 difference. Venous PO2 was always very low (≤7 Torr). Anaerobic metabolism made a significant contribution to ATP supply, indicated by a 3-fold increase in plasma lactate that resulted in an uncompensated metabolic acidosis. Respiration of isolated gill cells was not inhibited until below 5 Torr; because gill water PO2 always exceeded this value, hypoxic ion flux arrest in oscars [Wood et al., Am. J. Physiol. Reg. Integr. Comp. Physiol. 292, R2048-R2058, 2007] is probably not caused by O2 limitation in ionocytes. We conclude that metabolic depression and tolerance of anaerobic bi-products, rather than a superior capacity for O2 supply, allow oscar to thrive in extreme hypoxia in the Amazon. © 2008 Elsevier B.V. All rights reserved.
metadata.dc.identifier.doi: 10.1016/j.resp.2008.05.001
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