Chinook (king) salmon (Onchorhynchus tshawytscha) are a culturally and economically iconic species on the west coast of North America, yet nine ESUs (Evolutionary Significant Units) receive federal protection from the U.S. Endangered Species Act. Chinook salmon experience a period of high mortality (> 90%) upon first entering the ocean as juveniles. It has been hypothesized that ocean conditions influence juvenile salmon mortality by changing the quality of salmon prey, but research testing the effects of prey quality on salmon performance are limited. We conducted a 20-week experiment testing for the effects of prey quality on juvenile Chinook salmon growth, lipid composition, isotope signatures, and swimming performance. Salmon were reared for 12 weeks on three energetically similar diets enriched with two prey types (anchovy and krill) and two essential fatty acids (docosahexaenoic acid, DHA and eicosapentanoic acid, EPA). Based on previous studies using larvae, we predicted that fish reared on a diet rich in DHA (anchovy diet) would grow faster than fish fed a diet rich in EPA (krill diet) or a diet with equal ratios of DHA to EPA (krill:anchovy diet). From weeks 12-16, we adjusted rations to see if there was a carryover effect of dietary fatty acids on salmon growth and lipid reserves. Finally, from weeks 16-20, ration was withheld from all salmon before measuring critical swimming speed to assess a carryover effect on foraging capabilities and predator avoidance. Growth rates during the feeding study were similar (0.29 to 0.35 mm d-1). However, by the end of the experiment, salmon reared on the anchovy diet were on average 11 mm larger, had 17.9 mg g-1 more lipids, and swam 25 mm s-1 faster than salmon reared on the other formulated diets. These results provide support for the hypothesis that prey quality is important for juvenile salmon during a critical period in their early life history, and suggests that prey rich in DHA provides a survival advantage to salmon prior to experiencing their first ocean winter.