Gyrodactylidae ( Monogenea : Platyhelminthes ) gill parasites of Tetragonopterinae ( Characiformes : Characidae ) from the upper Paraná River floodplain , Brazil Gyrodactylidae ( Monogenea : Platyhelminthes ) parasitos branquiais de Tetragonopterinae ( Characiformes : Characidae ) na planície de inu

Aim: This study records Gyrodactylus neotropicalis and Anacanthocotyle anacanthocotyle in new hosts: Astyanax lacustris and Moenkhausia forestii, on the upper Paraná river floodplain. Besides, ecological aspects of the parasites distribution are explored. Methods: Both host species were collected between March and September 2014; monogeneans were removed from the gills using a stereo-microscope and mounted in Hoyer or stained with Gomori’s trichrome and mounted in Balsam of Canada. Illustrations were prepared on a phase contrast microscope. Monogeneans were identified using the appropriate literature. Prevalance, abundance, mean intensity and intensity range were calculated to parasite species in each host. Results: Gyrodactylus neotropicalis and Anacanthocotyle anacanthocotyle are recorded in new geographic area, upper Paraná River floodplain, in new host species, A. lacustris and M. forestii and in new infection site, gills. A. anacanthocotyle occur in higher prevalence, abundance and intensity parasitizing A. lacustris, while G. neotropicalis presented higher prevalence, abundance and intensity in M. forestii. Discussion: Gyrodactylus neotropicalis described by Kritsky & Fritts, 1970, parasite of Astyanax fasciatus (Cuvier), presented a different shield position between anchors than the specimens studied here; A. anacanthocotyle also described by Kritsky & Fritts, 1970 presented spicules in the cephalic region, what was not observed in the specimens studied here. Plasticity in parasitism may explain the difference between monogenean in different hosts. Conclusion: Until now, there was no record of this Gyrodactylidae species parasitizing Characidae fish in South America. Those parasites are the first Gyrodactylidae monogeneans described from A. lacustris and M. forestii.

as Anacanthocotyle sp.Therefore, until now, Anacanthocotyle genus is composed exclusively by A. anacanthocotyle, the type species.
With more than 450 species, Gyrodactylus von Nordmann, 1832 is one of the most diverse genus within the Monogenea (Harris et al., 2004).The high diversity of Characiformes contrasts with the scarcity of described species of the genus Gyrodactylus infecting these fishes.Currently, only six nominal species of Gyrodactylus have been recorded in Characiformes from the Americas (Razo-Mendivil et al., 2016).Besides, there is no registration for Gyrodactylidae parasitizing Tetragonopterinae in South America (Thatcher, 2006;Cohen et al., 2013).
During a helminthological study on the freshwater fishes Astyanax lacustris and Moenkhausia forestii, from the upper Paraná River floodplain, Anacanthocotyle anacanthocotyle and Gyrodactylus neotropicalis were found and recorded from the gills.
Monogeneans were removed from the gills using a stereomicroscope, killed in a 1: 4000 formalin solution and preserved in 5% formalin.Some specimens were mounted unstained in Hoyer's medium to study sclerotized structures.Other specimens, stained with Gomori's trichrome, were used to observe internal organs (Eiras et al., 2006).
Measurements are in micrometers (µm), with means followed by the range and number (n) of

Introduction
The fish fauna of the Neotropical region is the most diversified of the world, and represent about 24% of the global marine and freshwater fish species (Vari & Malabarba, 1998).The upper Paraná River floodplain has 182 fish species; of these, around 40 species belongs to the family Characidae (Graça & Pavanelli, 2007).Some Characidae species are widely distributed in Brazil, as Astyanax lacustris i (Lütken, 1875) and Moenkhausia forestii Benine, Mariguela & Oliveira, 2009, as known as "lambaris" or "piabas" (Benine et al., 2009).Although these fish species are not large commercially exploited, they present great ecological importance, as main items in the feeding of commercially valuable fish (Silva et al., 2012).They are also used as baits in sport fishing, ornamental fish, in fighting larvae of mosquitoes (Sato et al., 2006) and contribute to seeds dispersion (Andrian et al., 2001) (Kohn et al., 2006).
a intensidade média e a amplitude da intensidade para cada espécie de parasito em cada hospedeiro.specimens or structures measured in parentheses.

Resultados: Gyrodactylus
Illustrations were prepared on a Nikon (Eclipse E200) phase contrast microscope.After that, drawings were scanned and assembled using InkScape 0.91.Voucher specimens were deposited in the Instituto Oswaldo Cruz Helminthological Collection (CHIOC), Rio de Janeiro State, Brazil.Monogenean population of each species were described as proposed by Bush et al. (1997), based on parasite prevalence (P%), mean intensity (MI), mean abundance (MA) and intensity range (IR).

Results and Discussion
Anacanthocotyle anacanthocotyle (n=56) was found parasitizing three specimens of Astyanax lacustris (SL: 2.2-9.0 cm) and two specimens of Moenkhausia forestii (SL: 2.6-3.3 cm).Considering the same hosts, two specimens of A. lacustris and two specimens of M. forestii were parasitized by Gyrodactylus neotropicalis (n = 5).Comparing the distribution of A. anacanthocotyle and G. neotropicalis in each host, it is possible to note that A. anacanthocotyle occur in higher prevalence, abundance and intensity parasitizing A. lacustris, while G. neotropicalis presented higher prevalence, abundance and intensity in M. forestii (Table 1).
The distribution of Anacanthocotyle anacanthocotyle and Gyrodactylus neotropicalis in each host species was similar (Table 1) and only mean intensity (MI) was higher for A. anacanthocotyle parasitizing Astyanax lacustris, what can be explained by the aggregation of monogenean distribution.The variability in abundance among populations of the same host species used to be as large as that among different host species.In this case, parasites distribution could be a reflection of the importance of local abiotic and biotic effects, independent of the identity of the host species (Poulin, 1998).Remarks.Anacanthocotyle anacanthocotyle specimens were identified according to the morphologic characters presented by Kritsky & Fritts (1970); the species can be defined by the combination of the following characters: viviparous; two cephalic lobes; anchors and bars absent; 16 hooks, radially arranged.Anacanthocotyle anacanthocotyle is the only species described for the genus (Thatcher, 2006) and this is the first report from Brazil.Kritsky & Fritts (1970) described spicules in the cephalic region, above each cephalic lobe.However, spicules were not observed in the specimens analyzed here.Mendoza-Franco et al. (1999) described A. anacanthocotyle in a new geographic locality, but they did not mention the presence of spicules and the illustrations did not show spicules.Therefore, we did not consider such single character relevant enough to justify a new Anacanthocotyle species.
Gyrodactylus neotropicalis Kritsky & Fritts, 1970 can be defined by the combination of the following characters: spherical and ventral MCO, near the pharynx, with spinelets radially arranged; single pair of anchors, without filament, connected at their roots to each other by a shield and two bars; 16 hooks with similar size and shape, radially arranged (Kritsky & Fritts, 1970).
However, there is a difference between the Gyrodactylus neotropicalis from Kritsky & Fritts, (1970), parasite of Astyanax fasciatus (Cuvier), and the specimens observed here: shield position between anchors in haptor.Kritsky & Fritts (1970) described the shield connecting anchor at the middle, with shield situated below the deep root; but we observed the shield above the deep root (Figure 3).Secondary filament hook (SFH) was not observed, like expected according to the species description.Mendoza-Franco et al. (1999) illustrated shield above the deep root, and hooks without SFH, as we describe here.
Even though there are morphological differences between Gyrodactylus neotropicalis specimens, we did not consider these characters relevant enough to justify a new Gyrodactylus species.Since Astyanax lacustris and Moenkhausia forestii were not exclusive hosts for A. anacanthocotyle and G. neotropicalis, plasticity in parasitism may explain the difference between monogenean in different hosts (Poulin, 1998).
An a c a n t h o c o t y l e a n a c a n t h o c o t y l e a n d Gyrodactylus neotropicalis was first described parasitizing the external surface of Astyanax fasciatus (Cuvier) by Kritsky & Fritts (1970), in Costa Rica.Mendoza-Franco et al. (1999) described these parasite species in a new geographical locality, Yucatan Peninsula, Mexico, for the same host, but parasitizing fins.Jara (1986), made the only register until now for Anacanthocotyle genus in South America, parasitizing Bryconamericus peruanus on Peru.There are registers of Gyrodactylus from South America, including Tetragonopterinae or Characidae fishes (Thatcher, 2006)   Anacanthocotyle anacanthocotyle and G. neotropicalis are the first Gyrodactylidae monogeneans parasites described from Astyanax lacustris and Moenkhausia forestii.This occurrence in the upper Paraná river floodplain, southern Brazil, expands the parasites species geographical distribution and infection sites.
Although the present study provided new data on host spectrum and distribution of Gyrodactylidae species, the information about the fauna of monogeneans in south Brazil, specially related with small fishes, like Tetragonopterinae, is still limited.This information, together with data on the occurrence of monogeneans in South America, is necessary for better understanding the species composition, distribution, history and phylogeny of these parasites of freshwater fishes.

Figure 1 .
Figure 1.Map of the localization of the upper Paraná River floodplain.
but they are not specified, they are identified as Gyrodactylus sp.Rodríguez-Ortíz et al. (2014) described the occurrence of G. neotropicalis parasitizing the external surface of Poecilia sphenops (Valenciennes, 1846) in Costa Rica.