This study assessed the suitability and cost efficacy of an equal blend of canola oil (CO) and poultry fat (PF) as a supplemental dietary lipid source for juvenile Atlantic salmon. Quadruplicate groups of Atlantic salmon (∼400 g) held in 4000 L outdoor fibreglass tanks supplied with running (35–40 L min−1), aerated (dissolved oxygen, 7.88–10.4 mg L−1), ambient temperature (8.6–10.9°C) sea water (salinity, 26–35 g L−1) were fed twice daily to satiation one of three extruded dry pelleted diets of equivalent protein (488–493 g kg−1 dry matter) and lipid (267–274 g kg−1 dry matter) content for 84 days. The diets were identical in composition except for the supplemental lipid (234.7 g kg−1) source viz., 100% anchovy oil (AO; diet COPF-0), 70.2% AO and 29.8% CO and PF (diet COPF-30), and 40.3% AO and 59.7% CO and PF (diet COPF-60). Atlantic salmon growth rate, feed intake, feed efficiency, protein and gross energy utilization, percent survival and whole body and fillet proximate compositions were not affected by diet treatment. Cost per kilogram weight gain was about 10% less for fish fed diet COPF-60 than for diet COPF-0. Percentages of saturated fatty acids in dietary and fillet lipids varied narrowly. Moreover, percentages of 18:1n-9, monounsaturated fatty acids, 18:2n-6, n-6 fatty acids, 18:3n-3, and ratios of n-6 to n-3 fatty acids in the flesh lipids were directly related to the dietary level of CO and PF whereas 22:6n-3, the total of 20:5n-3 (eicosapentaenoic acid; EPA) and 22:6n-3 (docosahexaenoic acid; DHA), and n-3 fatty acids revealed the opposite trend. Percentages of 22:6n-3, EPA and DHA, and n-3 fatty acids were significantly depressed in fish fed diet COPF-60 versus diet COPF-0. We conclude that a 1:1 blend of CO and PF is an excellent cost-effective dietary source of supplemental lipid for Atlantic salmon in sea water.