Synopsis
The partitioning of O2 uptake between aquatic and aerial gas exchange and its dependence on ambient water PO2 was studied in the facultative air breathing teleost Synbranchus marmoratus, after acclimation to well aerated water and after acute and chronic exposure to hypoxic water. O2 uptake was also studied following acute air exposure and after prolonged entrapment in soil. Breathing rates during water and air breathing in response to reduced water PO2 and tidal volume during air breathing were also studied.
S. marmoratus satisfies its O2 requirement by water breathing alone until water PO2 falls below 30–50 mm Hg (switching PO2) depending on the acclimation history. Below the switching PO2, air breathing is adopted while active water breathing stops. The O2 uptake varied little for all groups when the principal mode of gas exchange changed at the switching PO2. The highest O2 uptake prevailed when the fish employed the mode of gas exchange in operation during the acclimation period (i.e. water breathing for normoxia-acclimated, air breathing for hypoxic-acclimated).
Acclimation to chronic hypoxia gave a much higher switching PO2 ≃ 55 mm Hg) than for the other groups (about 30 mm Hg).
S. marmoratus maintained its O2 uptake when acutely exposed to air. When entrapped in soil in an aestivating state, the O2 uptake was reduced to 25% of that in water or during acute air exposure. The overall gas exchange ratio for air breathing was very low (RE ≃ 0.1).
Branchial water pumping increased with lowering of water PO2. The rate of air breathing was independent of water PO2.
The findings are discussed in the light of the ecophysiological conditions confronting S. marmoratus.
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Eduardo, J., Bicudo, P.W. & Johansen, K. Respiratory gas exchange in the airbreathing fish, Synbranchus marmoratus . Environ Biol Fish 4, 55–64 (1979). https://doi.org/10.1007/BF00005928
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DOI: https://doi.org/10.1007/BF00005928