**1. Introduction**

Penaeid shrimps being euryhaline can adapt to thrive and survive in a wide range of salinity conditions. Shrimps are, therefore, cultured and reared under different farming conditions in tropical and subtropical countries. Water quality management is an important criterion in shrimp farming for survival and growth of the shrimp. The optimal salinity conditions for penaeid shrimp ranges differently for different species. *Penaeus monodon*, which can tolerate low salinity of 5 ppt to high salinity conditions of 40 ppt has optimal range of salinity (15–25 ppt) for optimal growth [1]; juvenile *Penaeus chinensis* grows best at 20–30 ppt salinity range [2]; the optimal conditions of salinity for growth was estimated to be in the range of 22–34 ppt

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

for *Penaeus latisulcatus* [3]. *Penaeus semisulcatus*, an Indo-Pacific species requires higher salinity (30–35 ppt) for growth [4]. Best performance (growth, survival, total biomass) for *Penaeus indicus* PL20 and PL60 at salinities between 20 and 30 ppt was observed after acclimation period [5]. Highest increase in biomass and production was observed at 25 ppt for *Penaeus merguien‐ sis* [6]. *Litopenaeus vannamei*, a native species of the Pacific coast is a very important shrimp species, which is cultured under semi-intensive and intensive conditions in many parts of world. The juveniles of this species have optimal growth and survival in salinity range of 33– 40 ppt [7]. It is also preferred for culture in low salinity water as it can tolerate very low salinities of 1–2 ppt.

However, the variable climate conditions result in drastic changes in abiotic factors causing stress to the shrimps during the culture period, which influences culture of euryhaline penaeids. In summer months, there is increase in salinity in ponds due to high evaporation rates and in rainy season the salinity decreases. The marine crustaceans are generally osmotic and ionic conformers in nature. The shrimps hypo-osmoregulate above the iso-osmotic point and hyper-osmoregulate below the iso-osmotic point through a osmoregulation mechanism.

In crustaceans, gills which are highly permeable external surfaces are the primary sites involved in osmoregulation. In the larval stages of penaeids, the typical features of osmore‐ gulatory epithelia are present in pleurae and branchiostegites [8]. The overall ion-transport and osmotic regulation process involves ions absorbtion or excretion between the external and internal medium through osmoregulatory organs, such as gills, the antennal glands that mainly function in urine production, and the gut in decapod crustaceans [9-10]

The crustaceans have two well-known important enzymes which are central to osmotic and ionic regulation and ion uptake. The transepithelial movement of monovalent ions requires the action of Na+ /K+ -ATPase or the sodium pump utilizing ATP as energy source. The other major enzyme involved in osmoregulation is transport-related enzyme carbonic anhydrase, which plays a role in producing H+ and HCO3- through catalysis of respiratory CO2, for counterions in Na+ and Cl<sup>−</sup> uptake. In penaeids, carbonic anhydrase is reported to be involved in both hyper- and hypo-osmotic regulation and is induced against low and high salinity exposure, indicating its role in ion uptake and excretion process [11].

In our study, we have constructed suppression subtractive hybridization (SSH) cDNA libraries to identify differentially expressed genes in shrimp *P. monodon*, in response to salinity stress. The SSH clones obtained from the forward SSH cDNA libraries (Figure 1) and reverse SSH cDNA libraries (Figure 2) constructed from gut tissues of shrimp exposed to low (3 ppt) and high (55 ppt) salinity on BLAST analysis, revealed several functional categories.

Similarly, we obtained several functional categories of genes from the forward SSH cDNA libraries (Figure 3) and reverse SSH cDNA libraries (Figure 4) constructed from gill tissues of shrimp exposed to low (3 ppt) and high (55 ppt) salinity conditions. These differentially expressed genes were subjected to RT-qPCR for gene expression analysis. Based on our study, we discuss herein in this chapter some of the important genes identified as differentially expressed in response to salinity stress in shrimp.

for *Penaeus latisulcatus* [3]. *Penaeus semisulcatus*, an Indo-Pacific species requires higher salinity (30–35 ppt) for growth [4]. Best performance (growth, survival, total biomass) for *Penaeus indicus* PL20 and PL60 at salinities between 20 and 30 ppt was observed after acclimation period [5]. Highest increase in biomass and production was observed at 25 ppt for *Penaeus merguien‐ sis* [6]. *Litopenaeus vannamei*, a native species of the Pacific coast is a very important shrimp species, which is cultured under semi-intensive and intensive conditions in many parts of world. The juveniles of this species have optimal growth and survival in salinity range of 33– 40 ppt [7]. It is also preferred for culture in low salinity water as it can tolerate very low salinities

102 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

However, the variable climate conditions result in drastic changes in abiotic factors causing stress to the shrimps during the culture period, which influences culture of euryhaline penaeids. In summer months, there is increase in salinity in ponds due to high evaporation rates and in rainy season the salinity decreases. The marine crustaceans are generally osmotic and ionic conformers in nature. The shrimps hypo-osmoregulate above the iso-osmotic point and hyper-osmoregulate below the iso-osmotic point through a osmoregulation mechanism.

In crustaceans, gills which are highly permeable external surfaces are the primary sites involved in osmoregulation. In the larval stages of penaeids, the typical features of osmore‐ gulatory epithelia are present in pleurae and branchiostegites [8]. The overall ion-transport and osmotic regulation process involves ions absorbtion or excretion between the external and internal medium through osmoregulatory organs, such as gills, the antennal glands that

The crustaceans have two well-known important enzymes which are central to osmotic and ionic regulation and ion uptake. The transepithelial movement of monovalent ions requires

major enzyme involved in osmoregulation is transport-related enzyme carbonic anhydrase,

in both hyper- and hypo-osmotic regulation and is induced against low and high salinity

In our study, we have constructed suppression subtractive hybridization (SSH) cDNA libraries to identify differentially expressed genes in shrimp *P. monodon*, in response to salinity stress. The SSH clones obtained from the forward SSH cDNA libraries (Figure 1) and reverse SSH cDNA libraries (Figure 2) constructed from gut tissues of shrimp exposed to low (3 ppt) and

Similarly, we obtained several functional categories of genes from the forward SSH cDNA libraries (Figure 3) and reverse SSH cDNA libraries (Figure 4) constructed from gill tissues of shrimp exposed to low (3 ppt) and high (55 ppt) salinity conditions. These differentially expressed genes were subjected to RT-qPCR for gene expression analysis. Based on our study, we discuss herein in this chapter some of the important genes identified as differentially


uptake. In penaeids, carbonic anhydrase is reported to be involved

and HCO3- through catalysis of respiratory CO2, for

mainly function in urine production, and the gut in decapod crustaceans [9-10]

exposure, indicating its role in ion uptake and excretion process [11].

high (55 ppt) salinity on BLAST analysis, revealed several functional categories.

of 1–2 ppt.

the action of Na+

counterions in Na+

/K+

which plays a role in producing H+

and Cl<sup>−</sup>

expressed in response to salinity stress in shrimp.

**Figure 1.** Differentially expressed genes from the forward SSH library of gut tissues of *P. monodon* under low (3 ppt) and high (55 ppt) salinity conditions

**Figure 2.** Differentially expressed genes from the reverse SSH library of gut tissues of *P. monodon* under low (3 ppt) and high (55 ppt) salinity conditions

**Figure 3.** Differentially expressed genes from forward SSH library of gill tissues of *P. monodon* under low (3 ppt) and high (55 ppt) salinity conditions

**Figure 4.** Differentially expressed genes from the reverse SSH library of gill tissues of *P. monodon* under low (3 ppt) and high (55 ppt) salinity conditions
