Osmoregulation of the Estuarine PrawnPalaemon Longirostris(Caridea: Palaemonidae)

Abstract

The caridean prawnPalaemon longirostris(Milne-Edwards) (Palaemonidae) occurs predominantly in the upper regions of large river estuaries in Europe, and reaches its northern limit of geographical distribution along southern parts of Britain (Smaldon, 1979). All post-larval stages are thought to live under dilute and fluctuating salinity conditions, although there are conflicting reports as to whether ovigerous females need to migrate to the sea at times of egg hatching (Gurney, 1923; Fincham & Furlong, 1984). The species has been known to be extremely euryhaline for some considerable time (Gurney, 1923), yet the salinity tolerance limits of larval (Antonopoulou & Emson, 1989) and post-larval stages (Campbell & Jones, 1989) have been established only recently. Apart from studies on salinity tolerances, and some preliminary measurements of blood and urine osmolality (Parry, 1957), the osmoregulatory adaptations ofP.longirostristo its dynamic habitat have not been investigated previously. The present paper describes the osmoregulatory responses ofP.longirostrisacclimated to a wide range of salinities, and also reports on the ability of individuals to compensate for sudden acute salinity change.