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 ov er the osmotic pressure and the ionic concentration of its haemolymph when exposed to a wide range of salinity between fresh water and its i sosmotic point. Sodium and chloride ions were regulated at almost iden tical concentrations over most of the salinity range tested. Calcium a nd potassium ions were hyperregulated at all salinities, whereas magne sium 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 conc entration is also regulated, but not as strongly as haemolymph chlorid e, and the two regulatory mechanisms appear to be discriminatory. The regulation of both strontium and bromide ions suggests that both may b e important in the physiology of this species.