First report of a species of Senga (Cestoda: Bothriocephalidae) in commercial Betta splendens (Actinopterygii: Osphronemidae) in Brazil.

Species of the genus Senga comprise a group of bothriocephalidean cestodes that predominantly parasitize freshwater teleost fishes, causing severe histopathological alterations due to scolex attachment to the digestive tract or obstruction of the intestinal lumen. The Siamese fighting fish Betta splendens is the type-host of Senga besnardi, the type species of the genus known only from the original description. Despite the importance of this fish species to ornamental aquaculture in Brazil, there are no prior records of this parasite in the Americas. Therefore, the present study aims to report the finding of B. splendens naturally infected with a bothriocephalidean cestode in a commercial fish farm from Brazil. In July 2024, four specimens of B. splendens exhibiting distension of the coelomic cavity were collected from an ornamental fish farm located in Patrocinio do Muriaé, Minas Gerais State. The animals were euthanized and submitted to parasitological analysis. Cestodes found in the fish were fixed, stained, and mounted for study by optical microscopy, with the aim of taxonomic identification. Cestodes were observed in the intestine of 3 out of 4 evaluated B. splendens, with infection intensities of 1, 8 and 10 cestodes per host. Morphological and morphometric analyses revealed that these specimens are indistinguishable from S. besnardi, particularly in the scolex morphology. However, given the complex taxonomy and the lack of molecular data for the species, the cestodes reported here are tentatively identified as Senga sp. This study represents the first report of Senga sp. infecting ornamental fish in the American continent.