Osmoregulatory ability and juvenile habitat preference in some penaeid prawns

Abstract

An investigation was made of the osmoregulation, over a salinity ( S) range 3–50‰, of early juvenile and adult penaeid prawns, whose nursery-ground preferences range from rivers of widely fluctuating salinity (banana prawn Penaeus merguiensis de Man; greasyback prawn Metapenaeus bennettae Racek & Dall) through open estuaries with very occasional low salinities (tiger prawn Penaeus esculentus Haswell) to open bays and lower estuaries with fairly stable high salinities (king prawn, P. plebejus Hesse). Adult banana prawns osmoregulated well between S 15–40‰ with isosmotic point ≈ S 27‰, but could not adapt below S 7 ‰, whereas adult greasyback prawns osmoregulated extensively from S 3–50 ‰ with isosmotic point ≈ S 23 ‰. Adult tiger and king prawns had limited osmoregulatory abilities with isosmotic points ≈ S 30 ‰ and lower lethal limits of ≈ S 10 and 7‰, respectively. Early juveniles of all four species were, however, all highly efficient osmoregulators and the curves of the three Penaeus spp. were almost identical below their isosmotic points, which were appreciably lower than those of the adults. Lower lethal limits were S 3‰ or below. It is concluded that nursery-ground selection by the species is unlikely to be determined by osmoregulatory ability. Possible factors determining nursery-ground selection are discussed.