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— Warmwater introductions <br />Warmwater systems are typically found at lower elevations, and summer water <br />temperatures exceed 23 -25 C. These are the most diverse aquatic systems, the <br />number of fishes can be large (over 40), and food webs diverse. Prominent warmwater <br />piscivores such as largemouth basses, have been coveted as recreational game fish, <br />cultured, and stocked into every conceivable habitat. But warmwater gamefish are <br />thought to have had a great adverse effect on native fishes wherever they have been <br />introduced. The ANSTF (1994) reported that centrarchids (i.e., largemouth bass, green <br />sunfish, bluegill, black crappie, and smallmouth bass) and ictalurids (i.e., channel catfish <br />and bullheads) were frequent contributors to the demise of native fishes nationwide. <br />A total of 11 nonnative centrarchids and 3 ictalurids have been introduced into <br />portions of the Missouri River. Many of these fishes have been linked with the <br />extirpation of native species, especially cyprinids (e.g. Lemly 1985, Fuller et al. 1999). <br />Although it can be anticipated that the predaceous adults of these species attack native <br />Missouri River species, it has been demonstrated that juvenile life stages also pose a <br />threat. Sabo et al. (1996) documented 18 types of agonistic behavior, including threats <br />and attempts to injure, in juvenile large -and smallmouth bass that were less than 50 <br />days post- hatch. <br />– largemouth bass. Adapted to warm lakes and slow- moving streams, this is one of the <br />most aggressive and predaceous freshwater fish in the world. Its introduction into <br />nonnative environments can alter entire systems. Carlander (1977) gives a listing of food <br />items consumed by various ontogenetic stages, which includes many taxa of fishes, <br />birds, crustaceans, reptiles, and amphibians. Fuller et al. (1999) provides a long list of <br />species that have suffered declines, extirpation, and extinction due to predation by <br />largemouth bass in the United States. Largemouth bass also have been transported to <br />exotic locations, and one account of an introduction into Lake Atitlan, Guatemal is <br />especially revealing because of impacts attributed to the fish, which included: ".. . <br />elimination of several native species of fish, reduction in total biomass of fish, predation <br />on young flightless giant grebes, and competition for the insects and crustaceans eaten <br />by the grebes" (Carlander 1977). <br />Largemouth bass has been widely introduced throughout the Missouri River <br />basin, and its range has expanded from the eastern parts of the Dakotas, Kansas, and <br />Nebraska all the way to the western limits of the basin. This fish is expected to be the <br />top piscivore in warmer (and especially more lacustrine) aquatic habitats. <br />– smallmouth bass. A fish of cooler temperate streams and lakes, smallmouth bass also <br />are aggressive predators. This fish hybridizes with several other centrarchids (including <br />spotted bass) and can decimate populations of small fishes by predation (Fuller 1999). <br />– sunfishes. Several sunfishes have expanded their previous ranges further west in the <br />19 <br />