© 2016, Springer Science+Business Media Dordrecht.Invasive Red Lionfish (Pterois volitans) continue to spread along tropical and subtropical coasts of the Western Atlantic, Caribbean, and Gulf of Mexico. They may have escaped natural controls present in their native Pacific, thus facilitating their immense success as predators in the Atlantic. We hypothesized that such ecological release would translate into faster individual growth and larger average body lengths in the invaded range relative to the native range. We used mark-release-recapture methods to monitor lionfish growth in two island systems in both the Pacific and the Atlantic. We compared the average individual lionfish growth rates among all four islands and between the two oceans, and compared population-level von Bertalanffy growth functions between oceans. While our study was limited to two sites in each ocean basin, we found consistent growth patterns within oceans and a significant difference between oceans, with lionfish in the Atlantic growing 1.25 to 2.25 times faster than lionfish in the Pacific. The von Bertalanffy model predicted larger average asymptotic lengths for the Atlantic population (322 vs. 225 mm). Given that lionfish consume prey up to half their body length, and that larger lionfish may be less vulnerable to predation, these findings, if broadly representative, suggest that invasive lionfish may consume larger native fish and may have higher survival than lionfish in their native range.