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<br />r <br /> <br />5 <br /> <br />The disappearance of native species is often attributed to predation and competition <br />by introduced fishes, but unequivocal examples are few (Taylor et ale 1984; Moyle et al. <br />1986). Evidence of direct impacts of introduced species on native fishes is difficult to obtain <br />(Schoenherr 1981) and is often masked by severe man-caused habitat alterations (Moyle <br />1976). Laboratory experiments may eliminate some confounding factors, but may not reflect <br />natural conditions. Field studies often imply interactions between nonnative and native <br />fishes, but most have not been designed to study this problem and many researchers obtain <br />their interaction data as an afterthought <br /> <br />Taylor et al. (1984) outlined the ecological effects of introduced fishes on native <br />fishes in native aquatic communities: <br />A Trophic interaction <br />1) Predation by introduced fishes, <br />2) Competition for food, or <br />3) Introduced fishes as a forage base. <br />B. Spatial interactions (aggressive effects or overcrowding) <br />1) Competition for habitat, <br />2) Competition for spawning space, or <br />3) Competition for feeding station. <br />C. Habitat alteration <br />1) Removal of vegetation by ( <br /> <br />~. <br />a consumption, <br />b. uprooting, or <br />c. increasing turbidity. <br />2) Degradation of water quality by <br />a siltation, <br />b. substrate erosion, or <br />c. eutrophication. <br />D. Hybridization, and <br />E. Disease or parasite introduction. <br /> <br />Ii <br />I, <br />1 <br />~ <br />f' <br />I <br /> <br />" <br />~, <br />I <br />ti <br />t <br />