Statistical analyses
To analyze the variation in TDF between weight classes, we conducted four different ANCOVAs with subsequent Bonferroni posthoc comparisons using Δ13C and Δ15N, for the two tissue types muscle and liver. We used final weight as a covariate with the attempt to adjust for the variation explained solely by growth (Fry and Arnold 1982). Additionally, we conducted four linear regressions with the Δ13C and Δ15N, for muscle and liver tissue respectively as dependent variables and SMR as the predictor in order to analyze the relationship between TDF and SMR. We compared SMR between the different weight classes using an ANCOVA with subsequent Bonferroni posthoc comparisons, including final weight as a covariate. The assumptions of normal distribution and homogeneities of variances were met for all parametric analyses. We used IBM SPSS (version 25) for statistical analyses.