1 Chapter - I INTRODUCTION Aquaculture is one of the world’s fastest growing food production systems increasing at a rate of 8% annually. Freshwater aquaculture in India is dominated by carps, which contribute about 87% of the total freshwater fish production. Fish are invariably subjected to physical, chemical and biological stressors. Stress is an unavoidable component in aquaculture practices, which is associated with transportation, handling, netting, water and sediment quality, vaccination and disease treatment. Aquaculture contributes to the livelihoods of the poor through improved food supply, employment and income opportunities. The Fisheries and Aquaculture Department (FAO) has defined the role of fish aquaculture which contributes to national food self-sufficiency through direct consumption and through trade and export activities. Current aquaculture does contribute to overall food supply by increasing the production of popular fish, thus reducing prices and by broadening the opportunities for income and food access (McKinsey, 1998; Sverdrup-Jensen, 1999). Thus aquaculture is indicated to be an important system for local food security through reduced vulnerability to unpredictable natural crashes in aquatic production, improved food availability, improved access to food and more effective food utilization (FAO, 2003a). Furthermore, the role of aquaculture can be assessed by looking at its impact on a variety of different aspects of food security base on core indicators: stability of food supply, availability of food, access for all to supplies and effective biological utilization of food. Fish is one of the sources of proteins, vitamins and minerals, and it has essential nutrients required for supplementing both infants and adults diet (Abdullahi et al., 2001). According to Adekoya and Miller (2004), fish and fish products constitute more than 60% of the total protein intake in adults especially in rural areas. According to FAO (2006), to maintain the present per capita fish consumption level of 13 kg per year, 2.0 million metric tons of fish food would be required. It has been noted by some researchers that the only means of meeting up with this annual fish demand for the country would be through a pragmatic option of intensive fish farming (Ezeri et al., 2009). Fish play an important role in human nutrition in India, particularly to people of coastal areas. Good and adequate nutrition plays a very important role in the expression 2 of mental, physical and intellectual qualities in human. To ensure access to the nutritionally adequate food for the improvement in the quality of diet of a poor person in the society, fish is the only medium which can serve the very purpose. They have the ability to reduce blood lipid level, particularly serum triglycerides (Boberg, 1990) and also have a good source for human nutrition due to their therapeutic role in reducing certain cardiovascular disorders (Stickney and Hardy, 1989; Ahmed, 2011). Fishes are widely used because pollutants present in food chain cause ill-effects and death of aquatic animals. Therefore, the problem of metal pollution is one of the major health problems in the persons who eat sea foods. Due to metal pollution, cellular level damage has been observed, which possibly affect the ecological balance. Fish are often at the top of aquatic food chain and may concentrate large amounts of some metals from the water (Mansour and Sidky, 2002). Metal bioaccumulation is largely attributed to differences in uptake and depuration period for various metals in different fish species (Tawari-Fufeyin and Ekaye, 2007). Multiple factors including season, physical and chemical properties of water (Kargin, 1996) can play a significant role in metal accumulation in different fish tissues. The gills are directly in contact with water. Therefore, the concentration of metals in gills reflects their concentration in water where the fish lives, whereas the concentrations in liver represent storage of metals in the water (Romeo et al., 1999). Fishes are subjected to stress conditions very often in the natural environment and have developed physiological and biochemical adaptations to cope with that or minimize or eliminate the deleterious effects, which are called, stress response. The stress response is divided into primary, secondary and tertiary responses (Goos and Consten, 2002; Ham et al., 2003; Davis 2004). Stress hormones (catecholamines and corticosteroids) are considered as primary responses and physiological changes are considered as secondary responses. The change in the somatic growth and population is considered as tertiary responses. Stress disturbs the fine internal balance, homeostasis and has further detrimental effects on behavior, growth, reproduction, immune function and disease tolerance (Chen et al., 2004). The effect of stress resulting from aquaculture practices on fish and methods of minimizing such effects have received considerable attention through the years (Barton and Iwama, 1991; Mazik et al., 1991; Cech et al., 1996). The stress induced by common 3 practices such as handling, crowding, transport, or poor water conditions can increase the incidence of diseases and mortality and salinity fluctuations undoubtedly impose stress on the physiology of the fish which can modify their structure and is therefore an important factor affecting the economics of aquaculture (Tsuzuki et al., 2001; Usha, 2011). Fish as a bioindicator species can play an important role in the monitoring of water pollution, as they respond with great sensitivity to changes in the aquatic environment (Lindstrom-Seppa et al., 1981; Smolowitz et al., 1991). Pesticides affect growth and nutritional value of fish, when their concentration in water exceeds the critical maximum limit (Arunachalam et al., 1980). Pesticides are not highly selective but are generally toxic to many macrophytes, non-target organisms such as fish (Ayoola, 2008; Franklin et al., 2010). Pollution of water has emerged as one of the most significant environmental problem of recent times. Not only there is an increasing concern for rapidly deteriorating supply of water but the quantity of utilizable water also fast diminishing. The wide array of pollutants discharged into the aquatic environment may have physico-chemical, biological, toxic and pathogenic effects (Goel, 2000). Most of the industries discharge their waste without proper treatment which cause change in physical, chemical and biological characteristic of water. The release of untreated industrial effluents into aquatic system seriously affects aquatic biota and their production. The deterioration of water quality day by day is due to the discharge of untreated effluents that demand urgent measures to assess pollutions (Mazher Sultana and Dawood Sharief 2004). Environmental pollutants, especially the metals are shown to pose serious risk to many aquatic organisms by changing genetic, physiological, biochemical and behavioral parameters (Prafulla Chandra Rout, et al., 2013). The most common pollutants which are toxic to fishes include heavy metals, pesticides, detergents, effluents and so on (Akpor, 2011). The heavy metals from several industrial, mining and other sources enormously contribute to the pollution of aquatic bodies causing address impact on biota including fishes. The fishes among the aquatic habitants, are the most susceptible and more vulnerable to containments than any other aquatic animals (Shivani Sharma, et al., 2014). 4 Water pollution is a major problem of this century and addition of pollutants changes the natural qualities of water (Voltz et al., 2005). Pesticides are known to contaminate a number of inland water bodies closer to areas of pesticide applications. Although pesticides are needed for the management of pests, their harmful effects on non-target organisms cannot be ignored. Pesticides leave residues in water and mud even several days after being sprayed in the adjacent crop fields. Pesticides affect growth and nutritional value of fish, when their concentration in water exceeds the critical maximum limit. The reproductive potential of fish is affected, when reared in water containing pesticide residues (Moore and Waring 2001). The major source of water pollution is domestic, agricultural and industrial wastes which are discharged into natural water bodies (De, 1996). Mason (1997) categorized chromium as one of the most toxic metal in freshwater. Chromium enters the aquatic environment through erosion and leaching from soil. Prolonged exposure of sublethal and least lethal chromium doses exceeded the maximum safe limit for metal accumulation in tissues (Taman et al., 1998; Aslam et al., 2011). Water pollution is recognized globally as a potential threat to both human and other animal populations which interact with the aquatic environments (Biney et al., 1987; Svensson et al., 1995). A number of organic and inorganic wastes in industrial and domestic effluents are responsible for water pollution. Fish is a natural and aquaculture freshwater and marine systems are exposed to pollutants, pathogens and xenobiotic substances which cause stress to these aquatic organisms. The conventional laboratory toxicity studies cannot be extrapolated to the natural environment because they lack ecological realism (Benson and Black, 1990). Variability and interaction of environmental factors in natural habitats complicate the responses of organisms to contaminants (Adams et al., 1992 and 1996). Water pollution (Kawade, and Khillare, 2012)