4. Discussion
When submitted to graded hypoxia tamoata´ were able to
keep a constant V˙ O2 from normoxia (130 mm Hg) until a
PiO2 of 50 mm Hg, which was determined as being its
critical O2 tension (PcO2 — Fig. 1a). The V˙ O2 was kept
constant due to increases in gill ventilation which is related
to the increases observed in fR (Fig. 1b). Tamoata´
significantly increased the fR as soon as the PiO2 reached
90 mm Hg. However, the higher increases in this variable in
the subsequent hypoxic tensions were not effective to ensure
a constant V˙ O2 below 50 mm Hg.