OSMOTIC AND IONIC REGULATION IN THE GIANT MALAYSIAN FRESH-WATER PRAWN, MACROBRACHIUM-ROSENBERGII (DE MAN), WITH SPECIAL REFERENCE TO STRONTIUM AND BROMINE

Macrobrachium rosenbergii is able to exert a high degree of control over the osmotic pressure and the ionic concentration of its haemolymph when exposed to a wide range of salinity between fresh water and its isosmotic point. Sodium and chloride ions were regulated at almost identical concentrations over most of the salinity range tested. Calcium and potassium ions were hyperregulated at all salinities, whereas magnesium ions were always maintained at much lower concentrations than in the medium. The regulation of strontium ions has been demonstrated and appears to be linked to magnesium regulation. Haemolymph bromide concentration is also regulated, but not as strongly as haemolymph chloride, and the two regulatory mechanisms appear to be discriminatory. The regulation of both strontium and bromide ions suggests that both may be important in the physiology of this species.