ORIGINAL PAPER Invasive rainbow trout affect habitat use, feeding efficiency, and spatial organization of warpaint shiners Duncan Elkins • Gary D. Grossman Received: 11 April 2012 / Accepted: 22 August 2013 / Published online: 30 August 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Rainbow trout have been introduced to six of the seven continents and currently are widely stocked for sport fishing. Despite their broad distribu- tion, outside of New Zealand, little is known about the effects of rainbow trout on native species, especially fishes. We conducted experiments in an artificial stream to assess hypotheses that stocked rainbow trout significantly affected: (1) mesohabitat use, (2) forag- ing success, (3) social behavior, and (4) spatial organization of warpaint shiners (Luxilus coccogenis) a common native minnow found in southern Appala- chian streams, with similar patterns of microhabitat use to rainbow trout. We replicated experiments at high and low natural densities (two and five warpaint shiners) and spring/fall (12 °C) and summer (17 °C) temperatures. Treatments included: (1) a control (five warpaint shiners), (2) trout (five warpaint shiners and one rainbow trout), (3) large fish control (five warpaint shiners and one river chub) and (4) density control (six warpaint shiners). The presence of rainbow trout produced a shift by warpaint shiners from pool mesohabitats to shallower, higher velocity habitats with more variable substrata, as well as reduced prey capture success, feeding efficiency, and distance from the front of the tank (i.e., warpaint shiners moved closer to food release points), and increased the distance to the additional fish (i.e., avoidance of the rainbow trout). Negative effects on foraging behaviors were stronger in 12 °C treatments. In a realistic stream flume the presence of rainbow trout produced effects that likely influenced individual fitness of warpaint shiners. The potential effects of stocking rainbow trout on native non-game fishes, such as warpaint shiners should be assessed when implementing or evaluating stocking programs. Keywords Oncorhynchus mykiss Á Luxilus coccogenis Á Trout stocking Á Competition Á Feeding behavior Á Social behavior Á Habitat selection Introduction Invasive species are one of the primary causes of the loss of aquatic biodiversity world-wide (Jelks et al. 2008; Almeida and Grossman 2012). Since the nineteenth century rainbow trout, Oncorhynchus mykiss (Walbaum) have been stocked in streams and lakes worldwide for sport fishing and represent an invasive in most of these habitats (Welcomme 1988; Fausch et al. 2001; Crawford and Muir 2008). In 2004, approximately 9,960,000 kg of rainbow trout were stocked in waters of the United states (Halverson 2008), with stocking programs active in D. Elkins Á G. D. Grossman (&) Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, USA e-mail: grossman@uga.edu 123 Biol Invasions (2014) 16:919–933 DOI 10.1007/s10530-013-0548-2