Stable isotope signatures are used as tracers of foreign materials in ecosystems. Their applicability in aquaculture was evaluated in this study. The signatures of eight feed ingredients showed [delta]13C values between -12.92 to -25.85 and [delta]15N between 0.47 to 12.43. Three diets with different proportions of the above ingredients had [delta]13C values between -19.55 and -20.78 and [delta]15N values between 5.27 and 9.34. The signatures were identified in the feces and muscle of rainbow trout fed each diet, demonstrating the potential for isotope ratios to be used as tracers. Sediment from a commercial fish farm was sampled to determine if it had an isotope signature related to the feeds used ([delta]13C -20.12; [delta] 15N 6.51). Results revealed isotope signatures more related to the control sites of [delta]13C -25.24 and [delta] 15N 3.93 indicating that for this particular site, the feed isotopic signatures couldn't be used as tracers of aquaculture-derived organic matter.