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Received Oct 27, 2011; Accepted Nov 15, 2011
1. Introduction
The giant river prawn, Macrobrachium rosenbergii, is a commercially important shrimp widely distributed in India and neighboring countries. Euryhalinity is the ability of an aquatic organism to tolerate wide salinity variations without compromising life process. M. rosenbergii is a euryhaline species that can survive in a wide range of salinity conditions. M. rosenbergii grows in freshwater but migrates to saline water (~10 ppt) for the purposes of breeding and subsequent nursery rearing of larvae [1]. The estuarine environment is essential for the completion of larval metamorphosis and thereafter postlarvae undertake a return migration to the riverine region [2]. Migration is believed to be associated with the process of adaptability in different saline conditions. This species experiences different local microenvironments, especially salinity and temperature, during migration. As a result, they must have developed an osmoregulatory adaptive mechanism so as to survive in different environmental (saline) conditions.
Since M. rosenbergii migrates between brackish and fresh waters during their life cycle, this species will be suitable for studying underlining biochemical, physiological, and gene regulatory pathways. A change in gene expression has been an important component for stress management of living organisms [3–6]. However, very little information is available about variations in gene expressions related to salinity tolerance in M. rosenbergii.
Gill plays a significant role in modulating ion transport either during freshwater to saline water acclimation or vice versa [6–9]. A substantial decrease in K-phosphatase activity including lowered α-subunit protein levels of Na, K-ATPase, and a redistribution of enzyme activity into membrane fractions of different densities in salinity-acclimated shrimp (M. amazonicum) was documented [10]. Thus, gill tissues from shrimp exposed to fresh and saltwater should be one of the ideal organs for comparative genetic analysis of the molecular basis of physiological acclimatization. Most of the studies were restricted to one or small number of genes. The mechanisms of adaptability to saline water are expected to be a complex physiological process associated with branchial ion transport. It is essential to understand the complex physiological roles played by the gill.
The analysis of differential gene expression in the gill of shrimp exposed to saline water can reveal adaptive mechanisms to salinity stress. Identification of salinity-induced...