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Journal of Experimental Biology 36,546-555 (1959)
Published by Company of Biologists 1959

The Osmotic and Ionic Regulation of Asellus Aquaticus (L.)

A. P. M. LOCKWOOD ¹

¹ Department of Zoology, University of Edinburgh, and Department of Zoology, University of Cambridge

1. The freshwater isopod Asellus aquaticus can be adapted to media ranging in concentration from 0.088 mM./l. NaCl to 200 mM./l. NaCl.

2. In fresh water O.P.₁ has a mean value of 150.5 mM./l. NaCl. In more concentrated media O.P.₁ approaches isotonicity with the medium.

3. The mean ion concentrations of the haemolymph of animals in fresh water are Na₁ = 137 m-equiv./l., Cl₁ = 125 m-equiv./l. and K₁ = 7.4 m-equiv./l.

4. Na and Cl account for most of O.P.₁ throughout the viable range of haemolymph concentration.

5. Evidence is presented which suggests that the animal is fairly permeable to salts and water.

6. During 8 days' starvation there is no change in O.P.₁, Na₁ or Cl₁. Sodium and chloride lost from the body can therefore be replaced by active uptake in the absence of food.