Evaluation of Dietary Lipids for Bull Trout

The Draft Recovery Plan for federally listed bull trout indicates artificial propagation may be required to meet recovery criteria for this species (USFWS 2002).  Artificial propagation will require a diet that meets all nutritional requirements of bull trout.  To aid in the development of nutritionally complete diets, we conducted a 12-week feeding trial to identify appropriate sources of dietary lipid for this fish.  The fish meal-free basal diet was top-coated with either marine fish oil, canola oil, linseed oil or a mixture of canola and linseed oils.  Each of the four dietary treatments was fed to triplicate groups of 12 bull trout initially weighing 1.6 g/fish.  At the conclusion of the feeding trial, weight gain, feed efficiency, survival and carcass proximate composition were not significantly different among bull trout fed the dietary treatments.  Carcass fatty acid composition varied significantly among fish fed the four diets.  Compared with bull trout fed dietary fish oil, fish fed dietary plant oils exhibited significantly higher carcass 18:2n-6 and 18:3n-3 concentrations and significantly lower carcass 20:5n-3 and 22:6n-3 concentrations.  Results of this feeding trial indicate dietary fish oil is not required for short term hatchery rearing of juvenile bull trout.