Ichthyofaunal diversity of the Canje River (Guyana): A distinctive lowland fauna between the Berbice and Corentyne Rivers, supported by a DNA barcode repository.

Guyana, and the Guianas more generally, exhibit some of the highest examples of biodiversity and regional endemism in the Neotropics. However, much of this diversity is still unknown, with the first modern list of freshwater fishes from Guyana compiled only in 2022. We continue to build on prior efforts in Guyana and provide an annotated list of fishes collected from the Canje River, a lowland tributary of the Berbice River. The Canje is also adjacent to the Corentyne River, raising the question of whether the Canje's fauna more closely resembles the Berbice or the Corentyne. A total of 92 sites were sampled in the Canje River during both high and low water seasons in 2023, 2024, and 2025. These expeditions yielded 87 species from 63 genera representing 28 families and seven orders. Characiformes dominated collections in terms of species. In addition to collecting several taxa once thought to be endemic only to the upper Berbice River, we report the first record of Sternopygus sabaji in Guyana, as well as several likely undescribed taxa. Contrary to expectations, the Canje was not particularly similar in faunal overlap to either the Berbice or the Corentyne, providing an example of high endemicity and beta diversity in neotropical lowland rivers.