Changes in volume of a brackish water prawn in different media

Abstract

The changes in volume in isosmotic medium show that the gut while taking in and giving out water through the mouth and anus is capable of altering the volume of the whole body. Such changes in volume, and therefore of pressure relations within, become significant when as the result of transfer to anisosmotic media, there is osmotic entry or escape of water, into and out of the haemolymph. In dilute medium the entry of water into the haemolymph increases its volume; and its pressure on the gut may not only check further entry of water but may facilitate filtration of hypotonic water from the haemolymph into the gut. In hyperosmotic medium, the loss of water and reduction of haemolymph volume are accompanied by increase of pressure from the more distended gut causing ultra filtration of dilute sea-water from the gut into the haemolymph. The decrease of the body volume in prawns acclimatised to dilute medium and the increase of body volume in concentrated medium, as well as the fluctuations in volume of prawns acclimatised to anisosmotic media, are features associated with the part played by fluid pressure in active regulation of water across the gut wall.