The effect of salinity on osmotic regulation and respiratory rate of the prawn Macrobrachium tenellum Smith, 1871 (Decapoda: Caridea: Palaemonidae)

Abstract

The effect of salinity on oxygen consumption rate and hemolymph osmolarity of the palaemonid prawn Macrobrachium tenellum (Smith, 1871) maintained at 0, 5, 10, 15, 20 and 25 psu was analyzed. Oxygen consumption rate was measured in respiratory chambers and osmolality from samples of hemolymph. Oxygen consumption rose significantly beyond 15 psu, with individuals showing hyper regulatory behavior from 0 to 10 psu, being able to maintain its internal solutes concentration (426–504 mmol kg–1) higher than that of the water (153–348 mmol kg–1). They acted as hypo-regulators from 15 to 25 psu as their internal solute concentration (454–562 mmol kg–1) was lower than that of the water (459–744 mmol kg–1). The isosmotic point was 505 mmol kg–1 at 16 psu, and survival was high in all salinities. The osmotic behavior of M. tenellum allows it to successfully invade fresh water by keeping constant the ionic and osmotic concentrations of both extra- and intra-cellular solute concentrations, always above fresh water, but varying its O2 consumption as salinity changes. The implications of such adaptations for the dispersal of the species into freshwater habitats is discussed.