EFFECTS OF THERMAL STRESS ON RESPIRATORY RESPONSES TO HYPOXIA OF A SOUTH AMERICAN PROCHILODONTID FISH, PROCHILODUS SCROFA

摘要

Oxygen consumption (VO2) 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 degrees C and in four further groups also acclimated to 25 degrees C and then changed to 15, 20, 30 and 35 degrees C. An increase in VO2, occurred with rising temperature, but at each temperature VO2, was kept constant over a wide range of O-2 tensions of inspired water (PiO(2)). The critical oxygen tensions (PcO(2)) were PiO(2) = 22 mmHg for 25 degrees C acclimated specimens and after transfer from 25 degrees C to 15, 20, 30 and 35 degrees C the PcO(2) changed to PiO(2) = 28, 22, 24 and 45 mmHg, respectively. Gill ventilation (V-G) increased or decreased following the changes in VO2 as the temperature changed and was the result of an accentuated increase in breath frequency. During hypoxia the increases in V-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 (PO2 similar to 70 mmHg). P. scrofa showed high tolerance to hypoxia after abrupt changes in temperature although its survival upon transfer to 35 degrees C could become limited by the capacity of ventilatory mechanisms to alleviate hypoxic stress.