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First published online June 15, 2007
Journal of Experimental Biology 210, 2311-2319 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02778

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Effect of aerial O₂ partial pressure on bimodal gas exchange and air-breathing behaviour in Trichogaster leeri

Lesley A. Alton^1,*, Craig R. White^1,2 and Roger S. Seymour¹

¹ Environmental Biology, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia, 5005, Australia
² School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

View larger version (30K): [in this window] [in a new window]   Fig. 1. (A) An example of the recorded fractional O2 content of the excurrent air from the respirometer (FEO2) (solid red line) over time. (B) The calculated coefficient of variation (CV=standard deviation divided by mean) (solid green line). A chosen CV threshold (red line in B) was used to derive the FIO2 baseline (blue line in A). (C) Calculated rate of aerial O2 consumption (O2) (green line) for each pair of recorded FEO2 and derived FIO2 values. A O2 threshold (red line) was chosen to separate breaths from noise.

View larger version (11K): [in this window] [in a new window]   Fig. 2. An example of the relationship between O2 uptake per breath and preceding apnoea duration for each fish at an aerial O2 partial pressure of 40 kPa. The slope represents aerial O2 consumption rate (ml min-1) during apnoea: Fish 1=0.0076; Fish 2=0.0069; Fish 3=0.0056; Fish 4=0.0051; Fish 5=0.0047; Fish 6=0.0033; Fish 7=0.0017.

View larger version (11K): [in this window] [in a new window]   Fig. 3. Effect of changes in aerial O2 partial pressure (PO2,air) on (A) air-breathing frequency (fab), (B) O2 consumption rate (O2; total, •; aquatic, ; aerial, ) and (C) mean O2 uptake per breath (VO2/breath) of Trichogaster leeri. (For fab, total O2, aerial O2 and VO2/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) fab=65.8–30.3log(PO2,air); (B) log(aquatic O2)=2.16–0.18log(PO2,air); log(aerial O2)=1.04+0.413log(PO2,air); (C) log(VO2/breath)= –1.01+0.98log(PO2,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.

View larger version (5K): [in this window] [in a new window]   Fig. 4. Effect of changing aerial O2 partial pressure (PO2,air) on the O2 partial pressure (PO2) in the air-breathing organ (ABO) of Trichogaster leeri at the end of apnoea assuming ABO volume is constant (•) and totally compliant () (N=2 for 5 kPa and N=6 for 10 kPa as individual breaths were invisible on the others; and N=7 for remaining treatments). Equations of regression lines: (constant ABO volume) log(end-apnoea ABO-PO2)=–0.0023+0.892log(PO2,air); (totally compliant ABO volume) log(end-apnoea ABO-PO2)=–0.084+0.977log(PO2,air). Treatments not denoted by the same letter are significantly different (a–e, constant ABO volume; f–j, compliant ABO). Measurements were made at 5, 10, 21, 40 and 60 kPa; symbols are offset for presentation. All data are shown as means ± s.e.m., but error bars are concealed by symbols at low PO2,air.

View larger version (4K): [in this window] [in a new window]   Fig. 5. Effect of changes in aerial O2 partial pressure (PO2,air) on the mean apnoeic O2 consumption rate (O2,ap) of Trichogaster leeri. The relationship is described by the logarithmic curve: O2,ap=–19.2+45.8log(PO2,air) (r2=0.63, N=2 for 5 kPa and N=6 for 10 kPa as individual breaths were invisible on the others; and N=7 for remaining treatments). Treatments not denoted by the same letter are significantly different. All data are shown as means ± s.e.m.