Dietary Marking of Otoliths, Fin Rays and Scales with Isotope Spikes

Artificial chemical marking of otoliths has emerged as a powerful method to assess stocking success and determine connectivity patterns. Although transgenerational and larval immersion methods have been validated, dietary transmission of enriched stable isotopes would allow minimal handling of animals and reduced expense for flow-through systems. We experimentally manipulated ¹³⁷Ba in diets and successfully marked otoliths in red drum Sciaenops ocellatus larvae, fingerlings and sub-adults as well as fin rays and scales of sub-adults. Marking success was dependent on rearing temperatures, indicating the need for sufficient growth to occur for consistently detectable marks. Second, we manipulated both ¹³⁸Ba and ⁸⁶Sr  in diets over four weeks and evaluated uptake of each isotope spike into otoliths.    Otoliths were successfully marked with Ba isotopes after two weeks, whereas dietary transmission of the Sr isotope spike was not successful.  A concentration-dependent mixing model explained differential dietary marking success marking success of Ba and Sr.  This mixing model will be useful for future workers to estimate the feasibility of dietary spiking in various systems with divergent water chemistry.  Dietary marking may be the method of choice where handling must be minimized or water chemistry cannot be manipulated.