In some very recent work we examined for evidence of adaptation in P. reticulata living in rivers in Southern Trinidad heavily polluted with typical petrogenic hydrocarbons including numerous branched alkylnaphthalenes (BANs) and toxic PAHs i.e. branched alkylbenzenes (BABs) derived from crude oil. Here we evaluate the loci under selection using RAD-seq analysis, using the restriction enzyme Sbf1. We genotype 8 fish from an extremely polluted river stretch in southern Trinidad and another 8 from a clean river stretch in the north of the country.