Effects of thermal stress on respiratory responses to hypoxia of a South American Prochilodontid fish, Prochilodus scrofa |
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Authors: | M N Fernandes W R Barrionuevo F T Rantin |
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Institution: | Department of Physiological Sciences, Federal University of São Carlos, P. O. Box 676, 13565-905, São Carlos, SP, Brazil |
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Abstract: | Oxygen consumption ( o2) and respiratory variables were measured in the Prochilodontid fish, Prochilodus scrofa exposed to graded hypoxia after changes in temperature. The measurements were performed on fish acclimated to 25°C and in four further groups also acclimated to 25°C and then changed to 15, 20, 30 and 35°C. An increase in o2 occurred with rising temperature, but at each temperature o2 was kept constant over a wide range of O2 tensions of inspired water ( Pi o2). The critical oxygen tensions ( Pc o2) were Pi o2= 22 mmHg for 25°C acclimated specimens and after transfer from 25°C to 15, 20, 30 and 35°C the Pc o2 changed to Pi o2= 28, 22, 24 and 45 mmHg, respectively. Gill ventilation ( G ) increased or decreased following the changes in o2 as the temperature changed and was the result of an accentuated increase in breath frequency. During hypoxia the increases in G were characterized by larger increases in breath volume. Oxygen extraction was kept almost constant at about 63% regardless of temperature and ambient oxygen tensions in normoxia and moderate hypoxia ( P o2∼70 mmHg). P. scrofa showed high tolerance to hypoxia after abrupt changes in temperature although its survival upon transfer to 35°C could become limited by the capacity of ventilatory mechanisms to alleviate hypoxic stress. |
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Keywords: | temperature hypoxia respiratory responses P scrofa |
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