An invasive amphipod (Crangonyx floridanus), found in 2007 in Lake Biwa, is an emerging environmental issue in the lake. There is a sympatric amphipod (Jesogammarus naritai) which is an endemic species to Lake Biwa, and it is thought to be affected by the existence of C. floridanus.In this study, we analyzed predation pressure upon the two amphipods from bluegills (Lepomis macrochirus), which are widely distributed in the littoral zone of the lake.The stomach contents of L. macrochirus revealed that both amphipod species were eaten. In addition, J. naritai was eaten more than C. floridanus, though C. floridanus was more abundant than J. naritai in the study site. This suggests L. macrochirus prefers J. naritai to C. floridanus. This preference can be explained by the difference of body size between the two amphipods.