Metacercariae in the brain of cf. (Characiformes: Erythrinidae) from Iguazú National Park (Argentina): do they belong to (Digenea, Diplostomidae)?

In Argentina, the family Diplostomidae is composed of eight genera: Szidat & Nani; von Nordmann; Dubois; Lutz; Railliet; Dubois; Dubois; and Diesing. During a parasitological survey of fishes from the Iguazú National Park we detected diplostomid metacercariae in the brain of cf. . Fish were caught using crab traps, transported alive to the field laboratory, cold-anaesthetized and euthanized by cervical dissection. Some metacercariae were heat-killed in water and fixed in 10% formalin and others were preserved in alcohol 96% for DNA extraction. They were sequenced for the partial segment of the 28S rDNA, internal transcribed spacer (ITS) rDNA and cytochrome c oxidase subunit I (COI) mtDNA genes. Phylogenetic reconstruction was carried out using Bayesian inference and the proportion (p) of absolute nucleotide sites (p-distance) was obtained. In the 28S rDNA tree, the metacercaria sequenced grouped as sp. The COI mtDNA p-distance between the metacercariae with was 0.01. There is a small number of ITS sequences for the Diplostomidae family deposited in the GenBank. The oral sucker, ventral sucker, holdfast organ and the distance between oral and ventral suckers are larger in the adult compared with the metacercariae. Additionally, hind-body length and width are larger in the adult due to the development of the genital complex. Further studies using an integrative approach will help confirm the affiliation of other species to the genus .