For decades, fish researchers believed in Gerking’s “restricted movement paradigm”, thinking that river-dwelling fish largely stay in the same place and rarely venture forth. But in recent decades, ecologists have harnessed the power of both advanced tags and improved genetic methods to directly estimate movement distances and average home ranges of different fish species. Now, a new paper has gathered in one place data from more than 200 direct movement studies and more than 200 genetic studies to estimate how far river fish more on average. The findings show that while some fish in each population stays largely in the same place, other individuals of the same species move vast distances—in one case, more than 1,000 km (600 miles). Median movements from the direct studies were 12 km, while genetic studies based on changes in DNA estimated median dispersal to be 1 km. Across species, both method were closely correlated, but some species dispersed very little (69 meters based on direct methods; 19 m based on genetics), while others were champion movers. The new research by Lise Comte of U.C. Berkeley, and SAFS professor Julian Olden, appears in the journal Fish and Fisheries.