Ionic regulation in relation to the moult cycle ofCrangon vulgaris(Fabr.) (Crustacea, Natantia) from brackish water

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Abstract
Investigations on the ionic regulation of the hæmolymph during the moult cycle of Crangon vulgaris (Fabr.) (Crustacea, Natantia) were made in a salinity of 10‰. Sodium showed a minimum immediately after ecdysis and a maximum in the intermoult stages, while potassium, which also is held at a level higher than the medium, showed a minimum in the intermoult stages and an increase prior to and after ecdysis. Calcium showed, contrary to species from fully marine areas, a minimum after ecdysis and then a rapid increase in calcium ion concentration and a slow decrease in the later intermoult phase and in the premoult stages. Magnesium, generally held at a very low concentration, showed an increase at ecdysis. Chloride varied in the same way as sodium. The changes in ion concentrations during the moult cycle can mostly be explained by an increased permeability and an increased water intake before the ecdysis and a swelling of the animal after ecdysis before the new exoskeleton has hardened.