On Dactylogyridae (Monogenea) of four species of characid fishes from Brazil

Material collected from the fishes from the dams and fish farms of the Departamento Nacional de Obras c ontra as Secas (DNOCS) and from the tanks of the Itaipu Hydroelectric Station was examined in order to analyze the index and the infestation of Monogenea. Specimens of tambaqui ( Colossoma macropomum ), pacu ( Piaractus mesopotamicus ), pirapitinga ( Piaractus brachypomus ) and the hybrid tambacu ( Colossoma macropomum X Piaractus mesopotamicus ) were examined and five species of Monogenea were identified including: Mymarothecium viatorum Boeger, Piasecki & Sobecka, 2002, Mymarothecium boegeri Cohen & Kohn, 2005, Notozothecium euzeti Kritsky, Boeger & Jégu, 1996, Notozothecium januachensis Belmont-Jegu, Domingues & Martins, 2004 and Anacanthorus penilabiatus Boeger, Husak & Martins, 1995 . Infection prevalence and intensity of infection and new data concerning Monogenea are presented.


Introduction
Brazil is internationally recognized as one of the main countries with a great pisciculture, with vast areas and a climate favorable for the development and implementation of freshwater fish cultivation. Colossoma macropomum and Piaractus mesopotamicus are among most commonly cultivated fish species in Brazil (Martins et al. 2002).
Parasites could cause on losses in piscicultural facilities, especially in the Neotropical region due to ecological characteristics that facilitate the rapid and constant spread of various parasites (Schalch et al. 2006). Because of these losses to the piscicultural enterprise by parasites it is obvious that further and more detailed studies of these pathogenic agents are necessary, including morphological characterization, understanding the relationships between parasites and hosts, and the influence of the parasitism on host health.
Studies regarding parasitism of fishes by the different groups of helminths in the pisciculture stations of the "Departamento Nacional de Obras Contra as Secas, DNOCS" in the localities of Pentecoste, Amanari, Sobral and Icó, in the state of Ceará, Brazil, demonstrated that high infection indices were shown by the Monogenea, mostly species of the family Dactylogyridae (Kohn et al. 2004) Continuing these studies, four Characidae species were examined to study Monogenea: Colossoma macropomum (Cuvier, 1916), "tambaqui", Piaractus brachypomus (Cuvier, 1918), "pirapitinga", Piaractus mesopotamicus (Holmber, 1887), "pacu" and the hybrid C. macropomum x P. brachypomum from DNOCS dams and fish farms and P. mesopotamicus from the Itaipu Hydroelectric Power Station reservoir, located at Foz do Iguaçu. The fishes from the dams were collected using dragnets and fishhooks and those from fish farms were collected using dragnets and fish traps and transported to the station's laboratories, where living specimens were maintained in barrels for subsequent examination.

Material and Methods
The Monogena collected were processed according to Boeger and Vianna (2006) and mounted on slides in Hoyer's medium to allow identification of the sclerotized internal structures.

Results
Twenty-nine specimens of Piaractus mesopotamicus collected at the Itaipu Hydroelectric Power Station reservoir were examined, of which 23 (79,3%) were parasitized by Monogenea. From the DNOCS fish farms, five specimens were also examined, with a 100% of prevalence. Of the total of 28 Piaractus brachypomus specimens examined from the DNOCS fish farms, 7 (25%) were parasitized by species of Monogenea.
Two hybrids of C. macropomum and P. brachypomus examined from the fish farms in the locality of Sobral were parasitized by M. boegeri, reported herein as a new host record.

Discussion
In the present study, the index of parasitism was analyzed from samples taken from areas with intensive fish culture, where high levels of infestation in the DNOCS fish farms and dams and in the Itaipu Hydroelectric Power Station reservoir were observed, confirmed by the large quantities of Monogenea (prevalence and intensity) collected during host examinations.
In C. macropomum, three dactylogyrid species were found: Notozothecium euzeti, N. januachensis and Mymarothecium boegeri. As shown in Table 1, the number of parasites specimens obtained was very high, principally of N. januachensis. The total number of specimens collected was 7342, removed from 18 out of 30 fish examined, of which 5277 (71.7%) were identified as N. januachensis.
Notozothecium euzeti was described by Kritsky et al. (1996) parasitizing the gills of Acnodon normani Gosline, 1951 (Characidae), from the Xingu River in the State of Pará. In the present study, N. euzeti was identified in a new host, Colossoma macropomum from the DNOCS fish farms in the State of Ceará.
Notozothecium janauachensis was described in Brazil by Belmont-Jegú et al. (2004), also removed from the gills of C. macropomum collected from Janauacá Lake, state of Amazonas and from the fish farms of "Centro de Aquicultura da Universidade Estadual Paulista", Jaboticabal, state of São Paulo. Prieto (1989) studied the effects of parasitism in C. macropomum in Cuba and identified two monogenean species, Anacanthorus spathulatus, Linguadactyloides brinkmanni, as well providing a description of an undetermined species, with a brief characterization of anchors and bars, suggestive of N. janauachensis. Fischer et al. (2003) studied the parasitic fauna of C. macropomum collected from the River Solimões and reported the presence of A. spathulatus and L. brinkamnii. Besides these species, the authors reported Notozothecium sp., though without any measurements or a detailed description of the parasites recovered. Considering that two species of the genus Notozothecium were identified in this work, it is impossible to establish which species the authors collected.
In Venezuela, Aragot and Moreno (1997) and Aragot et al. (2002) studied the epidemiology and pathology of Monogenea from C. macropomum, and reported infections by A. spathulatus and L. brinkmanni. Centeno et al. (2004) examined specimens of Colossoma macropomum and the hybrid C. macropomum x P. brachypomus and identified A. spathulatus, as well as several protozoans and myxosporidia.
The identification of different species of Notozothecium in Characid fishes widens the previously reported distribution of species of this genus, a fact that could be useful as a phylogenetic tool, further contributing to the elucidation of the evolution of these parasites and their hosts. Cohen and Kohn (2005) in C. macropomum collected at the fish farms of the DNOCS research stations in the state of Ceará. In the present work, this species was detected in the type host and in the hybrid C. macropomum x P. brachypomum, which is a new host record for this species.

Mymarothecium boegeri was described by
Comparison of the monogenean fauna identified in C. macropomum from several locations showed that different species were obtained in the present study (Table 2). Reports from Venezuela, Cuba and from different Brazilian regions identified two other monogenean species: Anacanthorus spathulatus and Linguadactyloides brinckmanni, parasitizing the gills of C. macropomum. These species were not recovered from fishes collected at the DNOCS research stations, showing a difference in the composition of the parasitic fauna among these locations. Notozothecium janauachensis has a wide distribution, reported from the Amazonas, São Paulo and Ceará states, besides the unidentified species reported from Cuba, which could well be this species. Unfortunately, no voucher specimens could be located to confirm the identification.
In the present study, Piaractus brachypomus and P. mesopotamicus were parasitized by two previously recorded species: Mymarothecium viatorum and Anacanthorus penilabiatus, the latter one presenting low abundance (Table 2). Boeger et al. (2002) parasitizing the gills of P. brachypomus in the River Odra, in Poland. Cohen and Kohn (2005) collected specimens of M. viatorum from P. brachypomus and from P. mesopotamicus in Brazil, confirming the occurrence of this species in the type host and in other congeneric species from the Neotropical region.

Mymarothecium viatorum was described by
Anacanthorus penilabiatus was originally described by Boeger et al. (1995)  Specimens of P. mesopotamicus showed high prevalence, and, as in P. brachypomus, M. viatorum was more abundant in the two regions studied. Martins et al. (2002) studied the parasitic fauna of P. mesopotamicus and reported that Anacanthorus penilabiatus presented the highest prevalence. In the same host, Lizama et al. (2007) also reported the higher prevalence of A. penilabiatus species upon A. spathulatus, Anacanthorus sp. and two unidentified species of Mymarothecium.
Studies of the helminth fauna in cultivated forms of C. macropomum and P. mesopotamicus were conducted, to determine levels of parasitism relative to occurrence and seasonality, demonstrating a high prevalence of Monogenea, but no specific identification of the species obtained has been published (Eiras et al. 1995;Martins and Romero, 1996;Martins et al. 2000;Tavares-Dias et al. 2001;Schalch and Moraes 2005;Schalch et al. 2006).
Two specimens of the hybrid Colossoma macropomum x Piaractus brachypomus were examined and showed high rates of infestation by a single species, M. boegeri. However, further studies should be conducted to confirm the uniqueness of this parasitism, since the two parental species were parasitized by three and two different species, respectively. Centeno et al. (2004) compared the parasitic fauna of C. macropomum with those of the hybrid C. macropomum x P. brachypomus from Venezuela and found high prevalence of Anacanthorus spathulatus in the two host species. The present study showed that hybrids from the state of Ceará were only parasitized by M. boegeri, which is not one of the most prevalent species in C. macropomum.
The fish species studied, belonging to the genera Colossoma and Piaractus (Characidae), are phyllogenetically closer. According to Kritsky et al. (1996), Mymarothecium and Notozothecium are apparently sister taxa, but patterns of association of species of these genera with their host differ: Notozothecium occurs in members of six host genera (Myleus, Acnodon, Mylesinus, Pristobrycon, Pygocentrus and Serrasalmus), whereas Mymarothecium is restricted to a single subfamily, parasitizing Pygocentrus, Pristobrycon and Serrasalmus. Kritsky et al. (1996) suggested that the associations of Notozothecium and Mymarothecium are relatively old, with the common ancestor of the genera occurring in an early serrasalmid form.