The Maroni is one of the most speciose basins of the Guianas and hosts a
megadiverse freshwater fish community. Although taxonomical references
exist for both the Surinamese and Guyanese parts of the basin, these
lists were mainly based on morphological identification and there are
still taxonomical uncertainties concerning the status of several fish
species. Here we present a barcode dataset of 1,284 COI sequences from
199 freshwater fish species (68.86% of the total number of strictly
freshwater fishes from the basin) from 124 genera, 36 families, and 8
orders. DNA barcoding allowed for fast and efficient identification of
all specimens studied as well as unveiling a consequent cryptic
diversity, with the detection of 20 putative cryptic species and 5
species flagged for re-identification. In order to explore global
genetic patterns across the basin, genetic divergence landscapes were
computed for 128 species, showing a global trend of high genetic
divergence between the Surinamese south-west (Tapanahony and Paloemeu),
the Guianese south-east (Marouini, Litany, Tampok, Lawa…), and
the river mouth in the north. This could be explained either by lower
levels of connectivity between these three main parts or by the exchange
of individuals with the surrounding basins. A new method of ordination
of genetic landscapes successfully assigned species into cluster groups
based on their respective pattern of genetic divergence across the
Maroni Basin: genetically homogenous species across the basin were
effectively discriminated from species showing high spatial genetic
fragmentation and possible lower capacity for dispersal.