Diet treatments of chironomid larvae-only and feed-only in the tank experiment, and no-feeding (i.e., live prey-only) in the pond experiment, served to model fish muscle tissue isotope δ value transitions to known, constant diets. At stocking, fish muscle tissue was about −19.0‰ in δ13C and 14.5‰ in δ15N (Fig. 1). Thereafter, muscle tissue δ13C and δ15N values faithfully responded towards the values of the known diets. The rate and magnitude of isotope δ value transitions in muscle tissue varied according to the difference between the initial muscle tissue isotope δ values, the isotope δ values for each diet (Table 1), the magnitude of heavy isotope enrichment during assimilation into tissue (i.e., TEFs), and fish growth rate in weight. For example, different TEF values for C and N isotopes caused δ13C values of fish muscle tissue in the chironomid-only treatment to increase by about 5‰ (Fig. 1C), but δ15N values to remain relatively constant through time
(Fig. 1D).