The Neotropical freshwater ichthyofauna contains over 5,600 fish species in a small area, making it one of the most diverse vertebrate ecosystems globally.
A survey in the Fitzcarrald region of southeastern Peru reveals high species diversity, with many fish species coexisting and a significant turnover between different habitats and tributaries.
Findings suggest that the fish species in Fitzcarrald are ancient due to geographical isolation and habitat specialization, rather than recent adaptive changes, helping to explain their rich biodiversity.