The emersion response of the Australian Yabby Cherax destructor to environmental hypoxia and the respiratory and metabolic responses to consequent air-breathing |
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Authors: | S Morris J Callaghan |
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Institution: | (1) School of Biological Sciences, Zoology (A08), University of Sydney, Sydney, NSW 2006, Australia e-mail: stevems@bio.usyd.edu.au, Tel.: +61-2-9351-2433/2040, Fax: +61-2-9351-4119, AU |
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Abstract: | The Australian Yabby Cherax destructor voluntarily emerges from water to breathe air with increased frequency as water PO2 decreases. When the water PO2 declined below 2.7 kPa the crayfish spent >50% of time breathing air. The respiratory gas transport, acid-base, ionic and
energetic status were quantified in simulations of this emersion behaviour to determine the benefits that the crayfish may
gain from switching to air-breathing. C. destructor initially showed an elevated O2 uptake rate on emerging from hypoxic water, but after 1 h the O2 uptake rate was not different from that of crayfish in normoxic water. During 3 h of air breathing, subsequent to 2.7 kPa
aquatic hypoxia, the haemolymph PO2 increased while oxygen content was essentially unchanged, although cardiac output increased 5-fold. The haemolymph PCO2 increased from 0.44 to 1.21 kPa after 3 h while the CO2 content increased from 3.47 to 8.66 mmol · l−1 and the pH decreased from 7.73 to 7.57 after 1 h in air. In air C. destructor eventually achieved an O2 uptake rate similar to that achieved in water. A general hyperglycaemia occurred without anaerobiosis. In air-breathing C. destructor, small changes in lactate appear to offset the decrease in haemocyanin-O2 affinity caused by acid Bohr shift. During air-breathing, decreased haemocyanin-O2 affinity assisted in maintaining O2 diffusion into the tissues, but the ATP content of the tail muscle decreased so that after 3 h in air the energy charge was
only 0.59. The data are consistent with a specific depression of the Emden-Meyerhof pathway, preventing either lactate formation
or oxidative phosphorylation in the tail muscle, despite a concomitant glycogenolysis.
Accepted: 26 February 1998 |
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Keywords: | Oxygen Acid-base Adenylates Cherax Air-breathing |
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