Shifts in [delta]15N signature following the onset of exogenous feeding in rainbow trout Oncorhynchus mykiss: importance of combining length and age data

The [delta]15N isotopic change of recently emerged rainbow trout Oncorhynchus mykiss due to diet shift from yolk sac to exogenous feeding was evaluated in a field study. The fit of a general model including both fish length and age in days as co-variables indicates that the specific [delta]15N of individual fish at any given time along the ontogeny is determined by its growth trajectory. The results suggest that estimations based on fish size alone could bias data interpretation and maternal origin determinations in partially migratory salmonids. [PUBLICATION ABSTRACT]