Ornamental sh are becoming increasingly popular, but the lack of knowledge regarding their various diseases is a major challenge. Skin diseases commonly found in freshwater sh include black spot disease (BSD), which is characterized by melanin deposits around the metacercariae of some trematode species. Since BSD remains poorly understood, this study describes an outbreak of BSD in Etroplus maculatus raised in outdoor ponds at a Brazilian sh farm. Metacercariae samples were collected, examined, and subjected to molecular phylogenetic analysis. The parasites were conspeci c to an unnamed species, Crassiphiala lineage 5, recently found in Brazilian birds (Megaceryle torquata). Sequences obtained for longifurcate cercariae of the planorbid snail Biomphalaria straminea from the same region were identical to our metacercariae of Crassiphiala sp. These results suggest that Biompahalaria snails are likely an intermediate host of this parasite on farms where E. maculatus was found to be infected. We provide the rst molecular evidence that Crassiphiala are the causative agents of BSD in sh from Brazil. Combatting snails and preventing access of sh-eating birds to outdoor ponds are strategies to control this disease in ornamental sh farms.