Fig. 3. The effects of acetazolamide (Az) injection followed by hypercarbia (Pw_CO2=13.6 mmHg) and the rapid lowering of Pw_CO2 (A) on ventilation and blood gas and acid-base status in tambaqui Colossoma macropomum, including (B) ventilation amplitude (V_AMP; N=8), (C) ventilation frequency (fV; N=8), (D) arterial P_CO2 (Pa_CO2; N=8), (E) arterial P_O2 (Pa_O2; N=6-7), and (F) arterial pH (pHa; N=8). Acetazolamide was injected at time=0 min, while the onset of hypercarbia and rapid water CO₂ washout are designated by the vertical broken lines. Values are means ± 1 S.E.M. Significant differences from the pre-injection (time=0 min) or pre-hypercarbic exposure (time= 35 min) values are indicated by an asterisk (one-way RM-ANOVA; P values for acetazolamide treatment and hypercarbia, respectively: B, 0.127 and 0.002; C, 0.569 and <0.001; D, <0.001 for both; E, 0.241 and 0.028; F, <0.001 for both). For the rapid lowering of Pw_CO2, significant differences from the initial value (time=50 min) are indicated by an asterisk or double-arrowhead line (one-way RM-ANOVA with P values <0.001 for all).