Map of the Contas River basin, Bahia, Brazil (at the top right corner, in green) showing the stretch of the Gongogi River sub‐basin where the sampling was performed. The 14 sampled locations are situated in the Gongogi River (sites 1, 4, 6, 7, 11 and 14), Cambiriba Stream (sites 8, 9 and 10) and other four tributaries (sites 2, 3, 5, 12 and 13). Sampled locations are colour‐coded according to which of the divergent mitochondrial lineages are present, with the Southern lineage in yellow and the Northern lineage in green. The circles are divided proportionally according to the number of individuals belonging to each mitochondrial lineage in cases of sympatry (i.e. sites 6, 7, 8, 9, 10 and 11), corresponding to the putative hybrid zone between divergent lineages. Small black arrows indicate the water flow direction of the Gongogi River and Cambiriba Stream