In this study,we used natural δ13C andδ15N contents of live prey and feed to quantify their relative contributions to tissue growth in freely foraging juvenile channel catfish in nursery ponds. We used the diet treatments of chironomid larvae-only in tanks, feed-only in tanks, and live prey-only (no feeding) in ponds to estimate the steady-state expression of these singular diets in muscle tissue under controlled conditions. The forced diet-switching treatment in the tank experiment (chironomid larvae to feed) provided proof of concept that stable isotopes can be used to quantify the timing and magnitude of diet switches that occur between foods with distinct isotope contents