Fig. 3. Effect of changes in aerial O₂ partial pressure (P_O2,air) on (A) air-breathing frequency (f_ab), (B) O₂ consumption rate (_O2; total, •; aquatic, ; aerial, ) and (C) mean O₂ uptake per breath (V_O2/breath) of Trichogaster leeri. (For f_ab, total _O2, aerial _O2 and V_O2/breath, N=3 for 5 kPa treatment as individual breaths were invisible on the others and N=7 for remaining treatments; for aquatic _O2 N=7 for all treatments.) Equations of regression lines: (A) f_ab=65.8–30.3log(P_O2,air); (B) log(aquatic _O2)=2.16–0.18log(P_O2,air); log(aerial _O2)=1.04+0.413log(P_O2,air); (C) log(V_O2/breath)= –1.01+0.98log(P_O2,air). Treatments not denoted by the same letter are significantly different (in B, a–c denote aerial _O2, d,e denote aquatic _O2). Measurements were made at 5, 10, 21, 40 and 60 kPa; some symbols are offset for presentation. All data are shown as means ± s.e.m.