Effects of organic plant oils and role of oxidation on nutrient utilization in juvenile

18 Producing organic fish diets requires that the use of both fish meal and fish oil is minimized 19 and replaced by sustainable, organic sources. The purpose of the present study was to 20 replace fish oil with organic oils and evaluate the effects on feed intake, feed conversion 21 ratio (FCR), daily specific growth rate (SGR) and nutrient digestibility in diets in which fish 22 meal protein was partly substituted by organic plant protein concentrates. It is prohibited to 23 add anti-oxidants to organic oils, therefore the effects of force-oxidizing the oils (including 24 fish oil) on feed intake and nutrient digestibility was furthermore examined. Four organic 25 oils with either a relatively high or low content of polyunsaturated fatty acids were 26 considered: Linseed oil; rape seed oil; sunflower oil and grape seed oil. Substituting fish oil 27 with organic oils did not affect feed intake (P>0.05), FCR or SGR (P>0.05) despite very 28 different dietary FA profiles. All organic plant oils had a positive effect on apparent lipid 29 digestibility compared to the fish oil diet (P<0.05), while there were no effects on the 30 apparent digestibility of other macronutrients when compared to the fish oil diet (P>0.05). 31 Organic vegetable oils did not undergo auto-oxidation as opposed to the fish oil, and the 32 fish oil diet consequently had a significantly negative effect on the apparent lipid 33 digestibility. Feed intake was not affected by oxidation of any oils. In conclusion, the study 34 demonstrated that it is possible to fully substitute fish oil with plant-based organic oils 35 without negatively affecting nutrient digestibility and growth performance. Furthermore, 36 plant-based organic oils are less likely to oxidize than fish oils, prolonging the shelf life of 37 such organic diets. 38 Implications 39 Organic trout farming is a small but growing industry. In near future it is anticipated, that all 40 ingredients in feeds for this segment should be organically approved. Organic plant oils 41