Fish otolith formation is key for understanding the incorporation of elements into biominerals. It is often assumed that the final step of biomineralization consists of inorganic precipitation as the fluid where biominerals form can hardly be sampled. Thanks to fish ear anatomy, this can be overcome with otoliths. By comparing otolith formation and inorganic precipitation, we proved that this assumption is not always true. Our findings could refine models and shed light on biomineralization.