Morphological, histopathological and molecular assessments of Prosorhynchoides sp. (Digenea: Bucephalidae) in Perna perna (Bivalvia: Mytilidae) mussels sampled off the coast of Rio de Janeiro, southeastern Brazil.

[Display omitted] • Histopathologic and stereomicroscopic analyses are complementary methods to better confirm the parasitism by sporocysts and cercariae in mussels. • The absence of gonads in the mussel mantle may be associated with parasitism. • New sequences of Perna perna and Prosorhynchoides sp. from the coast of Rio de Janeiro, Brazil are provided. Mussel production is expanding worldwide, and in Brazil the main species currently produced is the mussel Perna perna. Bucephalid trematodes have been recorded in P. perna but their larval identification is problematic. In this context, the aims of this paper were to evaluate the prevalence of bucephalids in P. perna , perform taxonomic and phylogenetic trematode studies, and analyze potential histopathological alterations in the infected host. Mussels obtained by fishers from Guanabara Bay, Rio de Janeiro, Brazil were weighed and measured, and internal organ tissues and parasites were collected. Of the 69 analyzed mussels, 24.6 % (17/69) were parasitized by bucephalid larvae. Sporocysts were located mainly in host mantle. Mussels presented sporocysts and cercaria within the connective tissue of mantle, all without associated inflammatory reactions. Parasite loads varied from less than 5 % to > 50 % of parasitized tissue. Histopathological examinations indicated that male or female gonads were not observed in 77 % (10/13) of parasitized mussels and in 4 % (2/56) identified as non-parasitized in the histology but previously classified as parasitized in the stereomicroscopic analysis. Thus, the absence of gonads may be associated with parasitism. Prosorhynchoides sp. is reported herein for the first time in mussels sampled on the coast of Rio de Janeiro, with genetic and histological data reported for the intermediate host, sporocysts and cercariae. New 28S rDNA, 18S rDNA and ITS1, 5.8S and ITS2 sequences are provided. [ABSTRACT FROM AUTHOR]