The Indo-Pacific lionfish species Pterois volitans and P. miles are piscivorous predators that were introduced probably via aquarium release to the northwestern Atlantic approximately 15 yr ago and rapidly spread and established through the Greater Caribbean. Possible ecological impacts of this invasion on native species are a legitimate cause for concern. Despite predictions that lionfishes will extend their range throughout most of the eastern coast of South America, they are yet to be recorded in Brazil. We pres- ent a perspective analysis of the lionfish invasion in the southwestern Atlantic by investigating patterns of fish species movement across the Amazon-Orinoco plume (AOP), a large freshwater and sediment runoff between the Caribbean and the Brazilian Provinces that repre- sents a ‘porous’ barrier to dispersal for reef organisms. We analyzed records of species that have recently crossed the barrier and found that the Brazilian Pro- vince contributes a significantly higher proportion of its endemic fauna to the pool of crossers, indicating that movements of vagrant species across the AOP are more common from Brazil towards the Caribbean than vice versa. Nevertheless, despite infrequent migration south- wards against the currents, our analysis indicates that such migration has occurred historically and has re- sulted in the establishment of new populations. Our analysis indicates that a combination of the effects of the AOP and prevailing currents along northern Brazil may slow the pace of the potential invasion, which could help eradication programs if action is taken before lionfishes become widespread and established in Brazil.