Effect of the Substitution of Fish Oil with a Mixture of Plant-Based Oils in Diets of Rainbow Trout (Oncorhynchus mykiss Walbaum) Fingerlings on Growth, Phosphorus and Nitrogen Excretion

A feeding trial was performed to determine the effect of substituting fish oil with a 1:1 mixture of soybean and linseed oil on growth, phosphorus and nitrogen excretion, and lipid deposition of rainbow trout fingerlings. Diets with soy protein concentrate and soybean meal were prepared with 25, 50, and 75% substitution of fish oil with plant oils. Soy protein concentrate and soybean meal were used with fish oil at 100% in the control diet. Triplicate groups of 15 juveniles with an initial weight of 0.74 ± 0.05 g (mean ± standard error) were fed the experimental diets for 70 days. Growth performance, protein, and lipid digestibility, oxygen consumption, nitrogen, and phosphorus excretion, and lipid deposition (liver and muscle) were determined. The mixture of plant oils did not affect the growth performance of fingerlings. Apparent digestibility of lipids decreased as the fish oil in the diet decreased. A significant decrease of phosphorus excretion was observed as plant oils in the diets were increased. Lipid deposition was higher in liver unrelated to plant oil concentration in the diet. The results show that it is possible to use high quantities of plant ingredients in the diets without affecting the growth performance and lipid deposition, as well as significantly decreasing phosphorus excretion