Fish Assemblages of Reservoirs, Illustrated by Lake Texoma (Oklahoma-Texas, USA) as a Representative System

We suggest six generalizations about the ecology of fishes of large, warm, reservoirs in the southern United States. We test these postulates with examples from more than 20 years of our studies in Lake Texoma (Oklahoma-Texas), and previous historic work in this impoundment. Such impoundments are dynamic systems in which precise predictions about fish faunas, local assemblages, or their potential effects in river-reservoir ecosystems are difficult. However, several generalizations can be supported: (1) fish faunas in reservoirs are a largely non-coevolved array of species, consisting of native and non-native species that may remain relatively unchanged for decades; (2) the fish fauna of a reservoir changes in response to introduction of some non-native species but not others; (3) The fish fauna of a reservoir can change in response to abiotic events that occur at a range of spatial and temporal scales, but effects may be inconsistent and transitory; (4) strong abiotic and biotic gradients in reservoirs influence fish distribution from uplake to downlake and from shallow to deep habitats; (5) Predictability of local fish assemblage structure in reservoirs is low and can vary between littoral and open-water zones; (6) Effects of fish on ecology of the reservoir relates to trophic groups represented, and to numbers of omnivorous fish.