3. Results
3.1. Respiratory responses to hypoxia
Fig. 1a shows the oxygen uptake of H. littorale after 1 h
of exposure to the different levels of PiO2. Tamoata´ was
able to regulate the V˙ O2 (independent of the water PO2)
until the PiO2 of 50 mm Hg (PcO2) was reached. However,
below this point, V˙ O2 decreased proportionally to the PiO2,
reaching the lowest V˙ O2 values at 16 mm Hg.
The fR of tamoata´ increased significantly at 91 mm Hg in
relation to the normoxic values. Respiratory frequency
increased progressively in the more hypoxic tensions, reaching
maximum values at 24 and 16 mm Hg, when this variable
tended to stabilize around 167 breaths min1 (Fig. 1b).
The fRA of tamoata´ remained fairly constant in the PwO2
interval of 140 to 50 mm Hg, the PcO2 calculated for this
species (see Fig. 1a). Below this O2 tension, fRA increased
significantly until reaching 4.5 breaths h1 in the PwO2 of
10 mm Hg. At 5 mm Hg, the fRA tended to decline in
relation to the PwO2 of 10 mm Hg (Fig. 1c).