Changes in the Canadian River fish assemblage associated with reservoir construction

The fish assemblage of the Canadian River in Texas historically was dominat ed by Hybognathus placitus and Notropis girardi. These species represented > 90% of fishes collected from the Canadian River in 1954-1955. Constructio n of two reservoirs on the Canadian River in the 1960s (Ute Reservoir, New Mexico, 1962; Lake Meredith, Texas, 1965) altered hydrologic conditions in the river and affected the fish assemblage. Downstream from Ute Reservoir, mean annual discharge decreased by about 38% after impoundment, but N. plac itus, N. girardi, and other mainstem species still dominate the assemblage. Downstream from Lake Meredith, mean annual discharge decreased by 76% and the historic mainstem fish assemblage has been almost completely replaced b y species that formerly were restricted to tributary streams. The magnitude of post-impoundment changes in the fish assemblage of the Canadian River a ppears to be related to the degree that discharge has declined, especially during the spawning season.