The core story: intertwined maternal and progeny signatures enclosed in the otolith.

synchrotron-XRF spectrometry acquisition hyperspectral dataset (.h5) and R script Analytical imaging via synchrotron analysis was used to study sagittal otoliths of four freshwater pipefish species exhibiting amphidromous or freshwater resident lifestyles. We undertook a hyperfine elemental scanning of a 25 μm diameter length area centred on the core, namely the pre-hatch zone, corresponding to the sagitta formed during embryogenesis. We analysed calcium (Ca), strontium (Sr), manganese (Mn), chromium (Cr), cobalt (Co) and nickel (Ni) and sulphur (S), the latter to count growth increments. Whatever the species, a Ca pit consistently marked the core; the amphidromous species exhibited Mn enrichment at the core and the sagitta forms a week before hatching. These results illustrate common otolith formation mechanistic processes. Sr and heavy metals’ signal in the pre-hatch zone were compared to their signal in the edge of the otolith, an area encompassing the adult freshwater (adFW) environmental signature. We found that Co and Ni otolith signals had no relation to environmental conditions, but it is worth looking into Cr as a marker of early-life environment. Finally, while we caution against the use of Sr:Ca ratio for life history interpretations at the core because of the Ca pit, the Sr signal analysis uncovered possible variations in the parental behaviour that potentially trigger newly hatched juvenile migration to sea or residency. Our results demonstrate that the microchemistry of otolith forming during early development is a melting of maternal signal during egg yolk elaboration, of the environmental signal during egg incubation and of individual physiology during early growth.