Fig. 5. Respiratory responses of zebrafish Danio rerio to acute hypoxia (A,B) or hypercapnia (C,D). Control fish were taken directly from the main zebrafish facility (filled circles, N=12) and were monitored in normal water for a similar period of time as the experimental fish (kept for 28 days in normoxic/normocapnic water) and acutely exposed to hypoxia or hypercapnia (unfilled circles, N=9 for hypoxia; N=14 for hypercapnia). (A,C) Changes in breathing frequency (f_R); (B,D) changes in relative breathing amplitude (opercular displacement). *Significant differences within the control or experimental groups; significant differences between the control and experimental groups; two-way RM ANOVA (P<0.05).