Exposure of the crayfish Austropotamobius pallipes to air resulted in an acidosis in the postbranchial haemolymph (pHa) and the abdominal muscle. The haemolymph acidosis was subsequently compensated and, after 24 h in air, pHa had returned to the settled, submerged value. The intracellular acidosis remained uncompensated throughout the period of aerial exposure.

When crayfish were first removed into air, lactate concentrations in the haemolymph and abdominal muscle increased substantially. After 24 h in air lactate concentrations in both compartments had returned towards submerged levels. Possibilities for the fate of lactate are discussed.

Re-analysis of haemolymph acid-base data for crayfish exposed to air (Taylor & Wheatly, 1981) revealed discrepancies between observed and expected base excess. Initially these may arise from exchanges of H+ or HCO3 with other compartments. During long-term air exposure, the removal of lactate from the haemolymph and an independent accumulation of base, probably from the mobilization of an internal source of bicarbonate buffer, result in the observed pH compensation.

Determination of base excess for the changes in abdominal muscle acid-base status after 3 h of exposure to air corroborated the results of the haemolymph analysis, suggesting a retention of H+ despite the efflux of lactate.

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