Unsustainable fishing practices have placed a heavy emphasis on aquaculture to meet the global shortfalls in the supply of fish and seafood, which are commonly accepted as the primary source of health-promoting essential omega-3 (n-3 highly unsaturated fatty acids). However, dietary fish oil is required for the production of omega-3-rich farmed fish and this commodity, in a vicious circle, is at present derived solely from wild fisheries. Decreasing global availability coupled with the highly variable price of this resource has forced the aquaculture industry to investigate the possibilities of alternative dietary lipid sources. This review attempts to compile all principal information available regarding the effects of fish oil replacement for the diets of farmed finfish, analysing the findings using a comparative approach among different cultured fish species. The review initially focuses on the present situation with regard to the production, availability and main nutritional characteristics of fish oil and the principal alternative lipid sources (such as vegetable oils and animal fats). Following this, the effects of fish oil replacement in finfish nutrition on feed quality, fish performance, feed efficiency, fish lipid metabolism, final eating quality and related economic aspects are presented and discussed.

Fish oil replacement in finfish nutrition

Due to its traditionally good availability, digestibility and high content of n − 3 HUFA, fish oil is the main lipid source in fish feeds. However, world demand for this product has grown significantly in recent years, whereas its production, based on fisheries landings, is static. The purpose of the present study was to assess the effect of partial replacement of fish oil in compound diets for gilthead seabream and seabass, by several vegetable oil sources, on growth, dietary fatty acid utilization and flesh quality. Five iso-energetic and isoproteic experimental diets were formulated (25% lipid content). Fish oil was the only added lipid source in the control (FO) diet, and it was included in the other experimental diets at a level high enough (40% of FO diet) to keep the n − 3 HUFA levels well over 3% in order to cover the essential fatty acid requirements of these species. Fish oil was replaced by soyabean oil (SO), rapeseed oil (RO) and linseed oil (LO) or a mixture (Mix) of them. Feed intake in all dietary groups was in the range of results obtained for commercial diets in both species, and growth and feed utilization were very good. The results show that, providing a minimum content of essential fatty acids in the diet, it is possible to replace up to 60% of the fish oil by SO, LO and RO or a mixture of them in diets for seabream and seabass, without compromising fish growth. Fatty acid composition of liver and muscle reflected that of the diet, but utilization of dietary lipids differed between these two tissues and was also different for the different fatty acids. Despite reduction in dietary saturated fatty acids by the inclusion of vegetable oils, their levels in fish liver were as high as in fish fed the fish oil diet, whereas, in muscle, levels were reduced according to that in the diet. Linoleic and linolenic acids were accumulated in the liver proportionally to their levels in the diet, suggesting a lower oxidation of these fatty acids in comparison to other 18C fatty acids. Regarding eicosapentaenoic acid (20 : 5n − 3; EPA), docosahexaenoic acid (22 : 6n − 3; DHA) and arachidonic acid (20 : 4n − 6; ARA), these essential fatty acids were reduced in the liver at a similar rate, whereas DHA was preferentially retained in the muscle in comparison with the other fatty acids, denoting a higher oxidation particularly of EPA, in the muscle. Some other PUFA increased despite their low dietary levels in seabream fed LO diets and in seabass fed SO diet, suggesting the stimulation of delta-6 and delta-5 desaturase activity in marine fish. Despite differences in fatty acid composition, fillet of fish fed vegetable oils was very well accepted by trained judges when assessed cooked.

Dietary lipid sources for seabream and seabass: growth performance, tissue composition and flesh quality

This study evaluated the suitability of flaxseed oil as a source of supplemental dietary lipid for fingerlings of rainbow trout (Oncorhynchus mykiss). Triplicate groups of the 30 fingerlings held under identical culture conditions were fed twice daily by iso-nitrogenous, iso-calorific and iso-lipidic diets for 8 weeks. Experimental diets consisted of 30.2% protein, 18.6 kJ g-1 energy and 16.5% lipid from fish oil (FO), flaxseed oil (FxO) and 1:1 blends of the oils (FFxO). Moisture, ash, protein, final body weight, specific growth rate, weight gain, feed conversion ratio, survival and hepatosomatic index were not affected by treatments but the percent of lipids was significantly highest in fish fed the flaxseed oil diet (FxOD). The condition factors of fingerlings reared on FxOD and fish and flaxseed oils diet (FFxOD) were significantly lower than those fed the fish oil diet (FOD). Protein efficiency ratio (PER) was significantly higher than those fed the FOD and FFxOD. Whole body fatty acid compositions mirrored those of diet treatments. The highest amounts of highly unsaturated fatty acids (HUFAs) were detected in fish fed 100% FO, which was significantly different from other treatments. In all treatments polyunsaturated fatty acids/saturated fatty acids (PUFAs/SFAs) and n-6/n-3 ratios were higher than 0.45 and lower than 4, respectively. Present results indicate the fingerlings can be reared on diets in which FO has been replaced with FxO, with no significant effects on fish performance.

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Effect of dietary flaxseed oil level on the growth performance and fatty acid composition of fingerlings of rainbow trout, Oncorhynchus mykiss

https://accedacris.ulpgc.es/jspui/bitstream/10553/669/1/5714.pdf

Alterations in fillet fatty acid profile and flesh quality in gilthead seabream (Sparus aurata) fed vegetable oils for a long term period. Recovery of fatty acid profiles by fish oil feeding

Fish Oils in Aquaculture: In Retrospect Sena S. De Silva, David S. Francis, and Albert G. J. Tacon Lipids in Aquafeeds J. Gordon Bell and Wolfgang Koppe The World's Oils and Fats Frank D. Gunstone Palm Oil and Saturated Fatty Acid-Rich Vegetable Oils Wing-Keong Ng and Veronique Gibon Soybean Oil and Other n-6 Polyunsaturated Fatty Acid-Rich Vegetable Oils Paul B. Brown and Steven D. Hart Rapeseed (Canola) Oil and Other Monounsaturated Fatty Acid-Rich Vegetable Oils Giovanni M. Turchini and Rodney J. Mailer n-3 Polyunsaturated Fatty Acid-Rich Vegetable Oils and Blends Douglas R. Tocher, David S. Francis, and Keith Coupland Terrestrial Animal Fats Dominique P. Bureau and David L. Meeker Alternative Marine Resources Rolf-Erik Olsen, Rune Waagbo, Webjorn Melle, Einar Ringo,and Santosh P. Lall New Alternative n-3 Long-Chain Polyunsaturated Fatty Acid-Rich Oil Sources Matthew R. Miller, Peter D. Nichols, and Chris G. Carter Minor Components in Fish Oil and Alternative Oils with Potential Physiological Effect Jana Pickova, Sabine Sampels, and Marc Berntsen Fish Oil Replacement in Starter, Grow-Out, and Finishing Feeds for Farmed Aquatic Animals Brett D. Glencross and Giovanni M. Turchini The Effects of Fish Oil Replacement on Lipid Metabolism of Fish Bente E. Torstensen and Douglas R. Tocher Welfare and Health of Fish Fed Vegetable Oils as Alternative Lipid Sources to Fish Oil Daniel Montero and Marisol Izquierdo The Effects of Fish Oil Replacement on Nutritional and Organoleptic Qualities of Farmed Fish Grethe Rosenlund, Genevieve Corraze, Marisol Izquierdo, and Bente E. Torstensen Index

Fish oil replacement and alternative lipid sources in aquaculture feeds

Impact of different dietary lipid sources on growth, lipid digestibility, tissue fatty acid composition and histology of rainbow trout, Oncorhynchus mykiss

M Gisvold

Papers

Impact of different dietary lipid sources on growth, lipid digestibility, tissue fatty acid composition and histology of rainbow trout, Oncorhynchus mykiss