The surgeonfish, Acanthurus bahianus, has crossed the Amazon–Orinoco outflow barrier

Dispersal varies among species according to different biological and environmental factors. It is known that there is strong genetic division between the Ocean Surgeonfish (Acanthurus tractus) and the Barber Surgeonfish (Acanthurus bahianus) in the Caribbean and southern Atlantic biogeographic provinces with relation to the Amazon–Orinoco outflows. We analyzed cytb gene sequence diversity from 149 individuals collected at five localities around Cuba between October 2006 and February 2010. As expected, most individuals had haplotypes identical or closely related to those previously reported for the Caribbean. However, south Atlantic lineage haplotypes were also found in all surveyed localities with frequencies around 5 %. This finding suggests that A. bahianus has dispersed in recent times across the Amazon–Orinoco barrier, probably because environmental perturbations have aided dispersal.