Predation may be responsible for the disparate distributions observed between predatory fish and shrimp in Puerto Rican streams. Adult shrimp (Atya lanipes) are only present above waterfalls that pose barriers to predatory fishes. Because we have not found Atya in fish stomachs, we believe that these diadromous shrimp avoid predation by migrating to locations above waterfalls. We conducted experiments in artificial and natural streams to test how shrimp respond to fish chemical cues. Using a y-maze with fish scent on one side, we found slight avoidance behavior toward 2 fish species. We also set up flow-through tanks in 4 headwater streams and added fish to 2 of them. We marked shrimp with unique colors in pools above and below the fish scent input. We recaptured shrimp with the expectation that shrimp exposed to fish scent would move upstream to avoid fish predation. We did not observe a decline in shrimp abundance or a change in movement patterns in the streams where fish scent was added. However, shrimp abundances did decline dramatically when fish were put into wire-mesh cages directly in the stream. We conclude that shrimp may avoid fish predation, but need more than chemical cues to detect their predators.