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(Ictalurus punctatus) and several species of bullheads were mentioned. Various <br />bait species were another frequently cited group and included most commonly the <br />red shiner (Cyprinella lutrensis), the fathead minnow (Pimephales promelas) and <br />"other baitfish." Rainbow trout (Onchorhynchus mykiss) and brown trout (Salmo <br />trutta) were cited in seven and six cases, respectively, primarily for having caused <br />problems though hybridization with native trout species or as predators of smaller <br />species." <br />A comprehensive assessment of the relative impacts of introduced fishes on the <br />native Missouri River fishes will require knowledge of habitat use, food preferences, and <br />reproductive ecology of the native fishes. Information about the introduced fishes also <br />will be required, including foods consumed, space utilized, behavior, and degree of <br />sympatry with the native fishes. Unfortunately, very little has been reported in the <br />published literature about the life histories of most of the native species considered at <br />risk. Except for federally listed and candidate species (i.e., pallid sturgeon, sturgeon <br />chub, and sicklefin chub) published sources available for the other species at risk <br />presented in this report point out that for most, little is known about specific habitat <br />requirements, food preferences, or reproductive ecology (e.g., Pflieger 1997). Ideally, <br />this information would have been obtained before habitats were altered and populations <br />of the native fishes declined. However, there is a great deal of information available for <br />assessing the degree of threats posed by various nonnative fishes introduced into the <br />Missouri River, because almost all of them have caused problems with native fishes <br />elsewhere. <br />Table 3 provides an accounting of fishes (common and scientific names provided) <br />that have been introduced into various locations in the lower, middle and upper Missouri <br />River. Introduced fishes considered to be threats to the native Missouri River fishes are <br />discussed below by cold -, cool -, and warm -water systems: <br />— Coldwater introductions <br />Coldwater systems include streams and lakes in which the temperature rarely <br />exceeds about 20° C for any period of time. Fish faunas are characterized by trouts, <br />whitefishes, sculpins, and a few species of minnows and suckers. Because most of <br />these systems are at high elevations and small, they are subjected to harsh conditions, <br />and food webs are short. <br />Coldwater fishes that have been introduced into nonnative ranges in the Missouri <br />River basin include different taxa: Pacific salmon and nonnative cutthroat trout of the <br />genus Oncorhynchus, European brown trout (Salmo), and chars (Salvelinus). These <br />fishes historically inhabited headwater streams and cold rivers, where they rarely interact <br />with warmwater fishes. However, widespread introductions have been made into deep <br />and thus, cold reservoirs and their tailwaters and many "blue ribbon" tailwaters have <br />been exploited by sport fishermen. During colder portions of the year, introduced <br />15 <br />