Phylogeny and morphology of Ovipleistophora diplostomuri n. sp. (Microsporidia) with a unique dual-host tropism for bluegill sunfish and the digenean parasite Posthodiplostomum minimum (Strigeatida)

SUMMARYMicrosporidia are diverse opportunistic parasites abundant in aquatic organisms with some species hyperparasitic in digenean parasites. In the current study, we describe a unique microsporidian parasite, Ovipleistophora diplostomuri n. sp. that has a tropism for both the bluegill sunfish Lepomis macrochirus, and its digenean parasite Posthodiplostomum minimum. Though the microsporidium first infects a fish, the subsequent infection causes hypertrophy of the metacercarial wall and degeneration of the P. minimum metacercariae within the fish tissue. Genetic analysis placed this species within Ovipleistophora and ultrastructural characteristics were consistent with the genus, including the presence of dimorphic spores within sporophorous vesicles. Meronts did not have a surface coat of dense material, which has been previously reported for the genus. This is the first Ovipleistophora species described that does not have a tropism for ovary. Genetics demonstrated that O. diplostomuri n. sp. groups closely within fish microsporidia and not other species known to be hyperparasitic in digeneans, suggesting that it evolved from fish-infecting microsporidians and developed a secondary tropism for a common and widespread digenean parasite. The high genetic identity to Ovipleistophora species demonstrates the close relationship of this unique microsporidian with other microsporidia that infect ovary.

Helminth fauna of two cyprinid fish (Campostoma ornatum and Codoma ornata) from the upper Piaxtla River, Northwestern Mexico

The helminth parasite fauna of 2 species of freshwater fishes from the upper Piaxtla River in northwestern Mexico was studied. A total of 41 cyprinids, corresponding to 20 Campostoma ornatum and 21 Codoma ornata were analyzed. Six species of platyhelminths were recorded, including 2 species of monogeneans (Gyrodactylus sp. and Dactylogyrus sp.), 3 species of digeneans (Posthodiplostomum minimum, Clinostomum complanatum, and Margotrema sp.), and 1 species of tapeworm (Bothriocephalus acheilognathi). Helminth parasite infracommunities were depauperate, showed low richness and diversity values, and were dominated by 1 or 2 helminth species. This pattern is consistent with that observed for the helminth parasite communities in other freshwater fishes in central and northern Mexico.

Helminth parasites of the pupfish Cyprinodon meeki (Pisces: Cyprinodontiformes), an endemic freshwater fish from North-Central Mexico

A total of 21 pupfish Cyprindon meeki was collected from the spring Abraham González, Durango, Mexico. Seven helminth taxa were recovered: Salsuginus angularis, Posthodiplostomum minimum, Clinostomum complanatum, Bothriocephalus acheilognathi, Cyclustera cf. ralli, Atactorhynchus duranguensis and Spiroxys sp. Among them, B. acheilognathi and A. duranguensis were the most frequent and abundant species. The remaining species were rare and found at low mean abundance. The observed species richness, individual parasite abundance, and diversity were low at component community and infracommunity levels. These features are in accordance with those recorded for other freshwater fish species in the Nearctic part of Mexico. Host feeding habits, along with its role as intermediate host, are suggested as the main factors in determining the helminth community structure in this fish species.