Dietary transfer of enriched stable isotopes to mark otoliths, fin rays, and scales

Artificial chemical marking of calcified structures, such as otoliths, has emerged as a powerful method to assess stocking success and determine connectivity patterns in freshwater and marine systems. Although transgenerational and larval immersion methods have been validated, dietary transmission of enriched stable isotopes to calcified structures would allow minimal handling of animals and reduced expense for flow-through systems. We experimentally manipulated Ba-137 in diets and successfully marked otoliths in red drum (Sciaenops ocellatus) larvae, fingerlings, and subadults, as well as fin rays and scales of subadults in as little as 2 weeks of exposure. Marking success of 100% was found for larvae and fingerlings reared at higher temperatures, indicating the need for sufficient growth to occur for consistently detectable marks. Spiked isotopes successfully marked fin rays (86% marked) and scales (100% marked) of subadults, providing a cost-effective tagging method that can be sampled nonlethally. Dietary marking of calcified structures may be the method of choice where handling must be minimized or water chemistry cannot be manipulated.