First report of Crassiphiala sp. (Trematoda: Diplostomidae) as an etiological agent of black spot disease in commercial ornamental fish from Brazil.

Ornamental fish are becoming increasingly popular, but the lack of knowledge regarding their various diseases is a major challenge. Skin diseases commonly found in freshwater fish 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 fish farm. Metacercariae samples were collected, examined, and subjected to molecular phylogenetic analysis. The parasites were conspecific 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 first molecular evidence that Crassiphiala are the causative agents of BSD in fish from Brazil. Combatting snails and preventing access of fish-eating birds to outdoor ponds are strategies to control this disease in ornamental fish farms.