The natural habitats of fishes are characterized by water movements driven by gravity, wind, and other animals, including human activities such as shipping. The velocities of these water movements typically fluctuate, and the resultant unsteadiness is exacerbated when the flow interacts with protruding objects, such as corals, boulders, and woody debris, as well as with surfaces, such as the bottom and banks. The importance of these ubiquitous unsteady water movements is reflected in increasing annual numbers of papers considering their impacts on performance and behavior of fishes swimming in “turbulent flows” (Tritico, 2009) or “altered flows” (Liao, 2007). The ability of fishes to stabilize body postures and their swimming trajectories when these are perturbed by turbulent flows affects 2species distributions and densities, and hence fish assemblages in various habitats (Pavlov et al., 2000; Fulton et al., 2001, 2005; Cotel et al., 2004; Depczynski and Bellwood, 2005; Fulton and Bellwood, 2005). Understanding impacts of turbulence on fishes is also important as human practices modify water movements, and as turbulence-generating structures become increasingly common, such as propeller wash, boat-created waves, shoreline hardening to control erosion, fish deterrents, and fish passageways (see Chapter 3 by Castro-Santos and Haro, this book; Wolter and Arlinghaus, 2003; Castro-Santos et al., 2008).