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Title
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Respiratory responses to progressive hypoxia in the Amazonian Oscar, **Astronotus ocellatus**
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Author
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Abstract
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| This study determined the respiratory responses to progressive hypoxia in oscar, an extremely hypoxia-tolerant Amazonian cichlid. Oscar depressed oxygen consumption rates (), beginning at a critical O2 tension (Pcrit) of 46 Torr, to only 14% of normoxic rates at 10 Torr. Total ventilation () increased up to 4-fold, entirely due to a rise in ventilatory stroke volume (no change in ventilatory frequency), and water convection requirement () 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¨Carterial PO2 difference. Venous PO2 was always very low (¡Ü7 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. |
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Language
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English
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Source (journal)
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Respiratory physiology and neurobiology. - Amsterdam, 2002, currens
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Publication
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Amsterdam
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2008
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ISSN
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1569-9048
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DOI
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10.1016/J.RESP.2008.05.001
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Volume/pages
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162
:2
(2008)
, p. 109-116
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ISI
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000258489000002
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Full text (Publisher's DOI)
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Full text (publisher's version - intranet only)
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