Abstract

During the intermoult period crayfish were able to adapt to an oxygen saturation level of 30% (ca. 3.2 mg 1^-l) at 11-12 °C in neutral water (pH 7.2). The adaptation was mainly respiratory; the haemolymph O₂ affinity increased markedly in hypoxia. This increase was probably due to the simultaneous increase in the haemolymph Ca²⁺ and Mg²⁺ concentrations. Acidification of the water alone (pH 4), without a reduction in the O₂ saturation level, did not affect the haemolymph constituents appreciably. In acid water (pH 4) depleted of oxygen (30% of sat.), however, respiratory adaptation did not seem to take place. On the contrary, difficulties in pH- and osmoregulation were apparent. The latter observations are of considerable importance in Finland, since construction of engineering works on the good crayfish rivers often results in simultaneous drops in both the oxygen content and the pH value.

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