Food Science and Technology 1(2): 21-29, 2013 http://www.hrpub.org DOI: 10.13189/fst.2013.010202 Effect of Dietary Vegetable Oils on the Growth Performance and Fatty Acid Composition of Fingerlings of Rainbow Trout,Oncorhynchus mykiss Ali Masiha 1 , Eisa Ebrahimi 1,* , Nasrollah Mahboobi Soofiani 1 , Mahdi Kadivar 2 1 Division of Fisheries, Department of Natural Resources, Isfahan University of Technology, Isfahan, 84156-83111, Iran 2 Department of Food science, College of Agriculture, Isfahan University of Technology, Isfahan, 84156-83111, Iran *Corresponding Author: e_ebrahimi@cc.iut.ac.ir Copyright © 2013 Horizon Research Publishing All rights reserved. Abstract This study evaluated the suitability of canola and flaxseed oils as source of supplemental dietary lipid for fingerlings of rainbow trout. Triplicate groups of the 30 fingerlings were fed twice daily by iso-nitrogenous, and iso-calorific diets for 8 weeks. Experimental diets consisted of 30.2% protein, 18.6 kJ/g energy and 16.6% lipid from fish oil, canola oil, flaxseed oil, 1:1 blends of fish and canola oils, 1:1 blends of fish and flaxseed oils, 1:1 blends of canola and flaxseed oils and 1:1:1 blends of fish, canola and flaxseed oils. Protein and lipid was significantly highest in fish fed the fish and canola oils diet. Condition factor of fingerlings reared on fish oil diet were significantly higher than other treatments. Protein efficiency ratio (PER) was significantly higher in fish fed the flaxseed oil diet and canola and flaxseed oils diet. The results of fatty acid profile revealed that flesh fatty acid composition is effected by dietary fatty acid composition. The highest amounts of HUFA n-3 were detected in fish fed fish oil diet, which was significantly different from other treatments. Present results indicate the fingerlings can be reared on diets in which fish oil has been replaced with canola and flaxseed oils. Keywords Rainbow trout; Canola oil; flaxseed oil; Fatty acid; Body composition 1. Introduction In the course of just a few decades, fish farming has developed into a highly productive and efficient industry for the production of animal protein for human consumption. In addition to good growing conditions, a prerequisite for productivity and economic sustainability in fish farming is a reliable supply of effective feeds. For various reasons, fish meal and fish oil have historically been the dominant raw materials in the production of fish feeds. Due to the development of more energy dense feed types together with the general growth of the aquaculture industry, a significant proportion of the total global production of fish oil is used for fish feed production. A lipid requirement equal to 100% of the world’s total fish oil production is estimated by the year 2010 [1]. While marine oils are superior in their fatty acid composition, they also contain a variety of toxic compounds including polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and dioxin-like polychlorinated biphenyls (DL-PCB), particularly the non-ortho and mono-ortho substituted PCBs [2-5]. These compounds are carcinogenic and immunosuppressive in humans [6-8]. It is well-known that lipid oxidation is one of the major problems in fish-derived food products. Polyunsaturated fatty acids (PUFA) are more easily oxidized than saturated fatty acids (SFA), and therefore, food products enhanced with the PUFA n-3 are also more prone to lipid oxidation. There are potential human health risks associated with increased consumption of oxidized PUFA n-3 products [9,10]. Another important factor to limit a more common use of PUFA n-3 enhanced food products is the development of off-flavors due to the lipid oxidation that may be offensive to consumers [11]. While it is obvious that a substitute must be found, replacing fish oil in aquaculture diets presents difficulties because most vegetable oils are relatively poor sources of n-3 fatty acids. Exceptions to this are flaxseed and canola oils which are rich in alpha linolenic acid (18:3n-3) (53% and 12% respectively) [12]. However, these oils are devoid of longer chain n-3 highly unsaturated fatty acids (HUFA n-3) and their inclusion in trout diets results in a significant decrease in the tissue levels of eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) [13,14]. Moreover, enhancement of omega-3 fatty acid content in rainbow trout fillet was observed in farmed rainbow trout and brook trout (Salvelinusfontinalis) as results of flaxseed oil inclusion in diet [15,16].