THE EFFECTS OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) ON THE USE OF SPATIAL RESOURCES AND BEHAVIOR OF ROSYSIDE DACE (CLINOSTOMUS FUNDULOIDES)

Rainbow trout (Oncorhynchus mykiss) and rosyside dace (Clinostomus fun duloides) exhibit substantial overlap in microhabitat use in Coweeta C reek, North Carolina, USA. We conducted a replicated experiment in an artificial stream to assess the effects of both the presence of rainbo w trout and dace density on: 1) microhabitat use, 2) agonistic behavio r, 3) social behavior and 4) feeding rates of dace. Our results demons trated that microhabitat use of dace was highly variable both among co mpetition treatments within a replicate and for the same competition t reatment among replicates. Moreover, the pattern of the differences be tween competition treatments was not consistent among replicates. As a result, we detected a significant effect of experimental replicate on dace microhabitat use but no significant competition effect. Trout ha d little effect on the behavior of dace and intraspecific aggression w as much more common than interspecific aggression. There were strong i nter-individual differences in the agonistic behavior of dace, and 94 of the 127 aggressive displacements observed were initiated by one or two highly aggressive individuals per replicate. We detected few signi ficant acclimation or time of day effects. The significant differences in microhabitat use and behavior observed within replicates appeared to be a consequence of differential initial settlement patterns of dac e or the presence of one or two highly aggressive dace in treatments. Hence, we do not believe that interspecific competition with rainbow t rout has a strong effect on microhabitat use by dace in Coweeta Creek.