Abstract
Oxygen uptake (V̇ o 2) and ventilatory parameters were measured during graded hypoxia in Nile tilapia ( Oreochromis niloticus) previously acclimated to normoxia (P o 2 ≥ 125 mmHg; 90% sat.) at 25 ± 1°C. V̇ o 2 was slightly increased as the oxygen tensions of inspired water (P i o 2) were reduced. Gill ventilation (V̇ G) increased significantly in response to hypoxia and resulted mainly in larger breath volume (V S,R) whereas breathing frequency was hardly changed. The increase in V̇ G was also accompanied by a reduction in oxygen extraction efficiency (E o 2-%). The metabolic cost of V̇ G was calculated as 3% of total V̇ o 2 in normoxia but increased to 18% during severe hypoxia (P i o 2 = 30 mmHg; 21% sat.). The results suggest that this species should not be exposed to long periods of low O 2 since portions of the metabolic energy are used by the ventilatory system to maintain O 2 uptake to the detriment of other metabolic functions such as weight gain and growth.
Published Version
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