Fig. 2. The effects of external injections of CO₂-enriched sea water (4 % CO₂; white symbols; N=9) or CO₂-free acidified sea water (pH 6.3; grey symbols; N=6) on ventilation amplitude (V_AMP) in dogfish (Squalus acanthias). The effects of (A) CO₂ and (B) acidified water are depicted as representative traces and as mean values (C). Control fish (black symbols; N=10) received bolus injections of sea water. The shaded box represents the 20 s period of injection. (D) The changes in V_AMP (V_AMP) at the 20 s time point. Data are shown as means +1 standard error of the mean. An asterisk denotes a statistically significant difference from the final pre-injection value (time zero). A double dagger denotes a statistically significant difference from the control and low-pH seawater groups. C, control. 1 mmHg=0.133 kPa.