Evaluation of Spirulina and plant oil in diets for juvenile steelhead (Oncorhynchus mykiss)

Abstract

As diets fed to juvenile steelhead (progeny of anadromous rainbow trout, Oncorhynchus mykiss) reared in conservation hatcheries contain relatively high levels of protein and lipid supplied primarily by fish meal and fish oil, a 12-week feeding trial was conducted to evaluate alternative ingredients for this species. Using a factorial design, Spirulina meal and a plant oil mixture were evaluated as partial or complete replacements of dietary fish meal and fish oil, respectively. Thus, two diets containing 0 or 50% substitution of Spirulina for fish meal were extruded and top-coated with fish oil or a 63:37 mixture of canola and flaxseed oils. Each of the four dietary treatments was fed to quadruplicate groups of 100 steelhead initially weighing 12.4 g/fish. Steelhead growth rate and feed efficiency were not significantly affected by partial replacement of dietary fish meal with Spirulina, but growth responses were significantly reduced by replacement of dietary fish oil with plant oil. Lipid and protein apparent digestibility coefficients (ADC) were significantly higher in steelhead fed the fish meal diets compared with fish fed the Spirulina diets and significantly higher in steelhead fed the plant oil diets compared with fish fed the fish oil diets. Whole body fatty acid profiles generally reflected those of the diets such that percentages of 18:2n-6 were significantly higher and n-3 polyunsaturated fatty acids (PUFA), including 20:5n-3 and 22:6n-3, were significantly lower in fish fed the Spirulina and plant oil diets compared with those fed the fish meal and fish oil diets. Plasma total cholesterol concentration was significantly reduced in fish fed the Spirulina diets and in fish fed the plant oils diets. Growth results suggest Spirulina is a suitable replacement for 50% of dietary fish meal for steelhead whereas a mixture of canola and flaxseed oil is not suitable as a complete replacement for fish oil in diets for this species.