FIRST REPORT OF AUSTRODIPLOSTOMUM COMPACTUM AND ITHYOCLINOSTOMUM DIMORPHUM IN TRAHIRA ( HOPLIAS MALABARICUS ) FROM THE MIDDLE COURSE OF THE RIO DOCE , MINAS GERAIS , BRAZIL

Austrodiplostomum compactum and Ithyoclinostomum dimorphum are two trematodes commonly found in trahira, but these parasites were never reported in trahiras from Rio Doce. Thus, the aim of this study is to describe the occurrence of A. compactum and I. dimorphum metacercariae in trahira from the middle course of the Rio Doce and to record the presence of eggs in I. dimorphum metacercariae. The parasites were identified and analyzed using methods described previously. There were found 10 A. compactum metacercariae in the aqueous humor of eyes in four of the trahiras and 12 I. dimorphum metacercariae encysted in the peritoneal cavity in five of the trahiras. Maceration of the I. dimorphum metacercariae revealed the presence of eggs. These results demonstrate the broad distribution of these parasites and the first report of these parasites in trahira from Rio Doce.

Our current knowledge of Brazilian ichthyoparasites indicates that there are approximately 1050 species from 620 different host species (Eiras et al., 2010).This number may be underestimated, since most studies on ichthyoparasitology are concentrated in southern Brazil (PavanElli et al., 1990;Gallio et al., 2007;Yamada et al., 2008).In southeast Brazil the ichthyo-parasite fauna has not been well explored (martins et al., 1999;Brasil-sato, 2002;ParaGuassú;luquE, 2007).Thus, the data obtained to date are not sufficient to elucidate the parasite fauna of Neotropical fishes.
The trahira, Hoplias malabaricus Bloch, 1794, has a wide distribution in Central and South America.This fish has nocturnal habits, tolerate low dissolved oxygen concentrations and its abundance is correlated with aquatic vegetation and shallow waters (shiBatta et al., 2002;rEis et al., 2003).According to luquE; Poulin (2007), there are currently 67 species of parasites recorded in H. malabaricus.Due to their feeding habits these species may act as definitive, intermediate and paratenic hosts to helminths (Barros et al., 2007).Austrodiplostomum compactum (Lutz, 1928) and Ithyoclinostomum dimorphum (Diesing, 1850) are trematodes commonly found in trahira.A. compactum is a digenetic trematode belonging to the order Diplostomida, whose metacercaria parasitise the eyes, brain, pericardium, muscle and peritoneal cavity of many Neotropical fishes (Eiras et al., 2010).A. compactum metacercariae have dorsoventrally flattened bodies, small subterminal oral suckers and two pseudosuckers in the anterior region, an acetabulum and short esophagus (Kohn et al., 1995).I. dimorphum is also a diplostomidae digenetic trematode whose metacercariae are found encysted in the muscle, gills, pericardium, peritoneal cavity and oesophagus of fish bodies and have very elongate, narrow, flat bodies with varying length and width (PavanElli et al., 1990).
The aim of this study was to describe for the first time the occurrence of A. compactum and I. dimorphum metacercariae in trahiras from the middle course of the Doce River, and to record the occurrence of eggs in I. dimorphum metacercariae.
The seven specimens of H. malabaricus Bloch, 1794, were collected in Lago Carioca, a complex of lagoons in the Parque Estadual do Rio Doce (PERD) (19S 46' 53" and 42W 35' 57").The specimens were collected using gillnets, standardized in various mesh sizes, mounted in the evening and removed the following morning.
The fishes were sedated with clove oil, euthanized and then fixed in formalin at 10% concentration and stored at the Museu de Zoologia "João Moojen" -Universidade Federal de Viçosa (MZUFV) until the analysis.
The specimens eyes were removed and the abdominal cavity was opened to search for and collect the internal parasites.The parasites were identified and analyzed using methods described by PavanElli et al. (1990), Kohn et al. (1995) and Eiras et al. (2010).Moreover, the parasites were subjected to maceration and observed under a stereomicroscope.
There were found a total of 10 A. compactum, metacercariae (Fig. 1) in the aqueous humor of eyes in four of the trahiras and 12 I. dimorphum, metacercariae (Fig. 2) encysted in the peritoneal cavity in five of the trahiras.The occurrence of these parasites were previously reported in other fish species in different geographic regions (PavanElli et al., 1990;Kohn et al., 1995;machado et al., 1996;silva -souza, 1998;Gallio et al., 2007;ParaGuassú;luquE, 2007;Yamada et al., 2008;zica et al., 2009;PaEs et al., 2010), but this is the first report of the presence of these parasites in trahira from middle course of the Rio Doce.
Based on analysis by stereomicroscope, the metacercariae of A. compactum presented a dorsoventrally flattened body, subterminal oral sucker, two pseudosuckers in the anterior region, an acetabulum and a short esophagus.The average length of the specimens was 1,121 μm (645-1,227 μm) and the average width measured in the midline of the body was 656 μm (312-987 μm).These morphological characteristics are consistent with other studies (Kohn et al., 1995).
The metacercariae is capable to penetrate in different structures such as body surface, fins, gills and mouth cavity, and the larvae migrate to the eye, and can cause exophthalmoses, retinal detachment, cataract, blindness, lesions and haemorrhages in various tissues, as well as obstruction of blood vessels (szidat; nani, 1951).Also these phenomena can lead to fish deaths in cases of high rates of infection (ovErstrEEt; curran, 2004).
I. dimorphum presented elongate, narrow, flat body.Morphological characteristics in according to PavanElli et al. (1990).It was not possible to compress the metacercariae between slides because their body was hardened due to their fixation in formalin.These digeneans occur preferentially in the south of Brazil (Gallio et al., 2007), but their distribution extends into southeast Brazil, namely Rio Doce, as described in the present study.
According to dias et al. ( 2003) and Pinto et al. ( 2004), I. dimorphum adults are found in the bird Ardea cocoi, a species found in the upper Parana region, and in birds belonging to the order Ciconiiformes from central-west Brazil.These birds distributed from Panama to Chile, Argentina and Brazil (sicK, 1997).A. cocoi has been reported in Parque do Rio Doce (PERD).This species occurs occasionally and is migratory (machado;FonsEca, 2000;lins, 2001;Faria et al., 2006) and may be acting as a disseminator of the parasite.However, there are no reports in the literature regarding the occurrence of I. dimorphum in birds from this region.
The macerate of the I. dimorphum metacercariae revealed the presence of eggs (Fig. 3).The occurrence of eggs in trematode metacercariae is not uncommon, for example, Coitocaecum parvum (Poulin;criBB, 2002) and Microphallus papillorobustus (WanG;thomas, 2002).The temporary or permanent absence of a definitive host may be responsible for the shortening of the parasite life cycle (Poulin;criBB, 2002).I. dimorphum has a complex life cycle, where molluscs, fish and birds act as hosts at different life stages of the parasite (dias et al., 2003).However, the role of each host is not yet fully understood.Thus, this first report on the occurrence of eggs in I. dimorphum metarcercariae from fish may help to explain the cycle of trematodes.This is the first report of the occurrence of A. compactum and I. dimorphum metacercariae in trahiras from the middle course of the Rio Doce.Fish infection by these parasites can cause major economic losses, related to pisciculture and fishing activities, due to    the reduction of fish stock and products of lower quality.This report is also important as it contributes to the knowledge of parasite distribution in Brazil.