Osmotic behaviour of shrimps and prawns in relation to their biology and culture

Abstract

The prawns which are useful for oultural purposes belong mostly to the deoapod families Penaeidae and Palaemonidae. Most penaeids are marine prawns which migrate to estuaries and brackish water in their young stages but go back to the sea to breed. A small number of them breed in coastal inlets and others are exclusively marine. Species of marine Palaemon are highly adaptable to lower salinities. The habitat of palaemonetes ranges from sea water to fresh water while Macrobraohium is largely a fresh water genus. Species of Macrobrachium include those which migrate from fresh water to brackish water during the breeding season. The marine penaeids and palaemonids show capacities for hypo-osmotic regulation when in sea water and high powers of hyper-osmotic regulation in brackish and fresh water. They have not developed extreme specialization as fresh-water inhabitants in that their normal blood osmotio values are high as compared with old established fresh-water crustaoea and they do not produce hypotonic urine for conservine salts. These features have endowed these prawns with unusual adaptational abilities to live in variable surroundings, although each species has its own optimal range. There is close correlation between enryhalinity and hyper-osmotic adaptation. There is a relationship between osmotic behaviour and temperature, and a combined influence of temperature and salinity is also in evidence. A fuller knowledge of isosmotic levels and critical evaluation of the influence of environmental conditions on osmotic and ionic behaviour would help to rationalize of prawn and shrimp cultural practices. The paper discusses the distribution of prawn and shrimps, their value in culture, existing knowledge of their osmotic properties, influence of salinity and temperature on their physiology and related problems.