Taxonomy and aspects of the ecology of Gyrodactylus sp. (Monogenea) parasitizing Pleuronectes americanus (Pleuronectidae) in Passamaquoddy Bay, New Brunswick

In an attempt to identify potential pathogens for the emerging flatfish aquaculture industry in Atlantic Canada, wild and cultured winter flounder (Pleuronectes americanus) from Passamaquoddy Bay were surveyed for viviparous monogeneans. Two species of Gyrodactylus were found: Gyrodactylus pleuronecti, Cone, 1981 and an undescribed species. Genetic sequences obtained sequencing the Internal Transcribed Spacers (ITS1 and ITS2) and the 5.8s ribosomal gene of the ribosomal DNA of the two gyrodactylids revealed a 3.5% difference. This observation supported morphologically based taxonomy, which indicated species status. Morphometrics of the taxonomically important structures were found to be significantly, eliminating the possibility of the two species representing ecophenotypic variants of a single species. Observations of live worms in the laboratory revealed that both species were morphologically conserved between generations. Host and site specificity experiments revealed that both species are host specific to winter flounder with G. pleuronecti having a significant preference toward the dorsal pigmented surface of the flounder, while Gyrodactylus sp. was found to occur more frequently on the ventral non-pigmented surface. Mixed infections of gyrodactylids on single host species typically involve two or more species that are members of different species-groups and thus relatively distant phylogenetically. However, the situation with winter flounder involves two gyrodactylids that not only belong to the same species group but may represent sister species.