Fig. 4. The effects of a bolus injection of CO₂-enriched water (5% CO₂) into the buccal cavity on (A) cardiac frequency (fH), (B) arterial blood pressure (Pa), (C) ventilation amplitude (V_AMP), (D) systemic vascular resistance (R_S), (E) cardiac output (b) and (F) ventilation frequency (fG) in rainbow trout Oncorhynchus mykiss previously subjected to sham extirpation (controls; open circles; N=22) or bilateral extirpation (filled symbols; N=11) of the first gill arch. Values are means ± 1 S.E.M.; significant differences (P<0.05) from pre-injection values (time=0) are denoted by asterisks, whereas significant differences (P<0.05) between control and extirpated fish are indicated by daggers. 1 mmHg=0.133 kPa.