Abstract Astyanax bimaculatus are small characids known as piabas or lambaris that form a complex encompassing 18 species, including cryptic species. The present study aimed to use DNA barcode to analyze populations of A. bimaculatus found in Maranhão hydrographic basins, comparing molecular diversity indices between populations from the other Brazilian basins. The results revealed the formation of 32 haplotypes (h = 0.9289; π = 0.0523). Seven haplogroups were formed with intrapopulation genetic distance ranging from 0 to 2%. The Maranhão populations of the Western Northeast Atlantic Region basins separated from the other analyzed basins, corroborating with the groups generated in BAPS and with the Bayesian Inference tree. The occurrence of exclusive OTUs for the Maranhão populations of the Western Northeast Atlantic Region was confirmed through delimitation models. Thus, the data from this study provide information on the genetic diversity of the A. bimaculatus complex with the detection of a different lineage for the State of Maranhão, contributing to the understanding of the group’s systematics. 1 species A 3 h 0.9289 09289 9289 0.0523. 00523 0.0523 . 0523 0.0523) 2 2% tree models Thus group s systematics 0.928 0928 928 0052 0.052 052 0.92 092 92 005 0.05 05 0.9 09 9 00 0.0 0.

Carcharhinus limbatus has a cosmopolitan distribution and marked genetic structuring, mainly because of its philopatric behavior. However, analysis of this structuring has not previously included South American populations. In the present study, we analyzed a sample of adult individuals collected on the northern coast of Brazil and compared the sequences of the mitochondrial control region with those of populations already genotyped. Relatively high haplotype diversity (12 haplotypes, genetic diversity of 0.796) was observed, similar to that in other populations but with a much larger number of private alleles. In contrast to populations studied previously, which were represented by neonates, the pronounced allelic variability found in the South American individuals may have resulted from migrations from other populations in the region that have yet to be genotyped. This population was also genetically distinct from the other Atlantic populations (Fst > 0.8), probably because of female philopatry, and apparently separated from the northwestern Atlantic group 1.39 million years ago. These findings indicate that the C. limbatus population from northern Brazil is genetically distinct from all other populations and should be considered as a different management unit for the protection of stocks.