The round goby, Apollonia melanstomus, is a recent invasive fish species in the Laurentian Great Lakes.  Field studies of round goby diet indicate that they are opportunistic foragers that feed predominately on dreissenid mussels but also consume fish eggs and fry, macroinvertebrates, and zooplankton. Their foraging activities have been shown to negatively influence native fish and invertebrate communities. However, we know of no studies assessing their growth on specific prey items. We conducted a controlled feeding experiment to test the null hypothesis that round goby growth will not differ when fed four different (exclusive) prey items: small fish, chironomids, dreissenid mussels, and zooplankton. Round goby grew at significantly higher rates on both fish and chiromonid diets (average = 0.13 g/day, stderr = 0.02 both cases) than on dreissenid mussels (mean = -0.03/day; stderr = 0.01) and zooplankton (mean = -0.04 g/day; stderr = 0.005) diets (F_3,23 = 23.6, P < 0.0001). Although dreissenid mussels are often the main component of round goby diets, they may not be the most beneficial for growth. Our results suggest that, energetically, round goby should opt to eat small fish and macroinvertebrates when available, increasing the risk of adverse food web effects.