From aquaria to ephemeral wetlands: spread of the microsporidian Pleistophora hyphessobryconis as a parasitic stowaway introduced via the aquarium trade

Microsporidians are increasingly recognized as emerging pathogens in aquatic ecosystems. Using an integrative morphological and molecular approach, we report Pleistophora hyphessobryconis infecting three native fish species (Titanolebias elongatus, Cnesterodon cf. decemmaculatus, and Potamorrhaphis eigenmanni) and the frog Boana pulchella in Argentina. This constitutes the first record of this parasite in the country, the first report in anurans, and the first documentation in the fish families Rivulidae and Belonidae. Partial SSU rDNA sequences obtained from all hosts clustered with reference sequences of P. hyphessobryconis and showed no genetic divergence. Light and transmission electron microscopy revealed pyriform spores with ultrastructural features consistent with the species, including anisofilar polar filaments. Infections were detected in both aquarium-held and wild specimens, suggesting multiple pathways for introduction and persistence. The occurrence in a frog highlights the potential for cross-taxon transmission into native amphibian populations. Our findings expand the known host range and geographic distribution of P. hyphessobryconis and emphasize the potential roles of the aquarium trade, environmental stress, and habitat connectivity in parasite dissemination. This study underscores the importance of integrative surveillance in assessing emerging disease risks in native aquatic fauna.