During the first two weeks of both experiments, fish were too small to measure stable isotope contents of individual fish, so the entire caudal peduncles of up to three fish from the same pond or tank were combined to achieve adequate dry mass for δ13C and δ15N measurements (Vander Zanden et al., 1998). During all subsequent weeks,measurements of muscle tissue in individual fish were performed. To account for anticipated size-dependent differences in fish diets within ponds, we selected the smallest, median, and largest fish (by weight) from each pond's weekly collection for stable isotope measurements (N= 3 fish/pond).