Growth response and fatty acid composition of rainbow trout (Oncorhynchus mykiss) fry fed diets containing different levels of soybean and egg lecithin

We investigated the effect of soybean and chicken egg lecithin on the growth performance, fatty acid profile and body composition of rainbow trout fry. Seven isonitrogenous and isolipidic diets were prepared by replacing 0, 2, 4 and 6 % soybean and egg lecithin instead of soybean oil in diets. Trout fry with initial average weight 120 ± 4.08 mg were randomly distributed in twenty-one 90-L tanks. Triplicate groups (165 fish per tank) of fry were fed to visual satiation at six meals per day for 40 days. Incorporation of 2 and 4 % egg lecithin led to increase in final weight, specific growth rate and weight gain compared with control group. Also, 4 % soybean lecithin had moderate effects on growth performance of fry. The fatty acid compositions of fry were influenced by dietary fatty acid. Fish fed egg lecithin showed higher amount of monounsaturated fatty acid than soybean lecithin and control groups. Fry fed soybean lecithin had significantly higher levels of polyunsaturated and n-6 fatty acid than egg lecithin and control groups. Soybean and egg lecithin induced higher amount of highly unsaturated fatty acid in lecithin groups compared with control group. The lipid and ash content of whole-body tissues were positively affected by percentages of soybean and egg lecithin in the diets. So 6 % soybean and egg lecithin induced higher amounts of lipid and ash body content. The results of our study indicated that dietary egg lecithin had growth-promoting effect, and rainbow trout fry had moderate lecithin requirement (at least 2 % as fed).