Osmotic Regulation in Metapenaeus ensis

Abstract

Experiments were conducted to determine salinity tolerance and some aspects of osmotic regulation in the prawn Metapenaeus ensis. 100% survival was observed in the full range of sea water concentrations (0-100% s. w.) at the end of the test period of 4 days. In distilled water survival was relatively short. In full sea water the haemolymph was virtually isotonic to the medium. This osmotic concentration was maintained as the medium was diluted to 30% sea water. In media more dilute than this haemolymph osmotic concentration fell rapidly but was markedly hypertonic to the medium. About 50% of the haemolymph osmotic concentration was accounted for by Na salts. The changes in haemolymph osmotic concentrations were partly due to the changes in sodium concentrations. The animals were found to be permeable to a certain degree and it was evident that regulatory mechanisms that actively adjust the composition of the haemolymph were present.