Proximate Composition of Freshwater Rainbow Trout

Rainbow trout, Oncorhynchus mykiss can be classified as the premier salmonid species. It is one of the most famous fish species in nature. At the same time, is also recognized and accepted as farmed fish species in many countries, because of its exceptional nutritive quality, rapid growth (Tekeliog, 2000) and exceptionally tolerant to environmental conditions (Simonovic, 2001). Worldwide production of rainbow trout was 537,000 tons in 2005 (FAO, 2007). Europe was the largest producer with 273,000, while Asia produces 97,000 tons (Vandeputte et al., 2008). O. mykiss is endemic to the Western region of North America. In 1973, Pakistan imported this species from Japan and introduced in its water bodies. Compared to other sources of protein, fish is an excellent source of proteins and essential nutrients for human diet (Arts et al., 2001; Fawole et al., 2007). In the developing countries, fish is considered as one of the best sources of protein (Louka et al., 2004). The nutritional value of the whole body is often used as an index of fish quality (Reinitz, 1983). The nutritional value of fish meat comprises the contents of moisture, dry matter, protein, lipids, vitamins and minerals, plus the caloric value of the fish (Evangelos et al., 1989; Steffens, 2006), while body composition and flesh quality are also essential characteristics of farmed fish species for human consumption. Body composition and flesh quality influence the consumer acceptance and human consumption (Kause et al., 2002). The measurement of some proximate profiles such as protein, lipids and moisture contents is often necessary to ensure that they meet the requirements of food regulations and commercial specifications (Waterman, 2000). Moreover, information concerning the chemical composition of freshwater fishes in general is valuable to nutritionists concerned with readily available sources of low-fat, highprotein foods such as most freshwater fishes (Mozaffarian et al., 2003; Foran et al., 2005), and to the food scientist who is interested in developing them into high-protein foods, while ensuring the finest quality flavor, color, odor, texture, and safety obtainable with maximum nutritive value (Mohamed et al., 2010). Body composition is also influenced by a great number of factors (Love, 1957; Weatherley and Gill, 1983a,b). It is observed that changes in the fish body composition are according to the size (Naeem and Ishtiaq, 2011), condition factor (Naeem and Salam, 2010; Naeem et al., 2011), and sex (Yousaf et al., 2011). Touhata et al. (1998) have shown that water temperature also affects the body composition of fish. While Suseno et al. (2010) have reported high protein and low fat content in fish due to increasing depth. Condition factor has been used as an index of growth and feeding intensity (Fagade, 1979). A change of weight at a particular length, or a change of length, without corresponding change of weight with alters ‘K’ (Weatherly and Gill, 1987). Therefore, the ‘K’ value for a given fish Pak. J. Agri. Sci., Vol. 53(2), 497-502; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.2653 http://www.pakjas.com.pk