Geographical origin of Amazonian freshwater fishes fingerprinted by Sr-87/Sr-86 ratios on fish otoliths and scales

Calcified structures such as otoliths and scales grow continuously throughout the lifetime of fishes. The geochemical variations present in these biogenic structures are particularly relevant for studying fish migration and origin. In order to investigate the potential of the Sr-87/Sr-86 ratio as a precise biogeochemical tag in Amazonian fishes, we compared this ratio between the water and fish otoliths and scales of two commercial fish species, Hoplias malabaricus and Schizodon fasciatus, from three major drainage basins of the Amazon: the Madeira, Solimoes, and Tapajos rivers, displaying contrasted Sr-87/Sr-86 ratios. A comparison of the Sr-87/Sr-86 ratios between the otoliths and scales of the same individuals revealed similar values and were very close to the Sr isotopic composition of the local river where they were captured. This indicates, first, the absence of Sr isotopic fractionation during biological uptake and incorporation into calcified structures and, second, that scales may represent an interesting nonlethal alternative for Sr-87/Sr-86 ratio measurements in comparison to otoliths. Considering the wide range of Sr-87/Sr-86 variations that exist across Amazonian rivers, we used variations of Sr-87/Sr-86 to discriminate fish origin at the basin level, as well as at the sub-basin level between the river and savannah lakes of the Beni River (Madeira basin)