Nematodes of Astyanax fasciatus ( Actinopterygii : Characidae ) and their parasitic indices in the São Francisco river , Brazil

The endoparasite fauna of Astyanax fasciatus from the upper São Francisco river was investigated and ecological parameters and morphological and morphometric data on the parasites are presented. A total of 74 specimens of banded astyanax were collected downstream from the Três Marias dam, municipality of Três Marias, Minas Gerais (18°12’32”S, 45°15’41”W) in January 2011 and January 2012. Eleven taxa of Nematoda were found: Contracaecum sp.; Hysterothylacium sp.; Goezia sp.; Brevimulticaecum sp.; Procamallanus sp.; Procamallanus (Spirocamallanus) saofranciscencis; Cystidicoloides sp.; Spinitectus rodolphiheringi; Rhabdochona sp.; Spiroxys sp.; and Eustrongylides sp.. The fauna of A. fasciatus consisted of by larval specimens of Contracaecum sp., Hysterothylacium sp., Brevimulticaecum sp., Cystidicoloides sp., and Spiroxys sp., and by adult specimens of P. saofranciscencis, whose prevalence was greater than 10%. Thus, this fish acts as an intermediate host of some species of larval nematodes especially, Anisakidae and Acanthocheilidae (Brevimulticaecum sp., new host record and new locality). It participates in transmitting species such Rhabdochona sp. to carnivorous fish and also acts as a definitive host for P. saofranciscencis and S. rodolphiheringi in the upper São Francisco river.


Introduction
Astyanax fasciatus (Cuvier, 1819) is popularly known as the banded astyanax and it is an abundant species in several drainage basins in the Americans (FROESE & PAULY, 2013).It is classified as a foraging species, and it is well distributed along the São Francisco river (BUCKUP et al., 2007), serving as an important food source for larger fish.Although banded astyanax do not have significant commercial value, they are often eaten as snacks, especially by the riverine population, and they are also used as bait for sport fishing (SANTOS et al., 1995).
The aims of this study were to investigate parasitism in A. fasciatus and contribute towards enriching knowledge of the ichthyoparasitology of the São Francisco river.Thus, it had the specific objectives of recording the species of parasitic nematodes of banded astyanax and also measuring their parasitic parameters (prevalence, mean intensity and mean abundance).

Materials and Methods
A total of 74 specimens of A. fasciatus were provided by technical staff of thee regional development company CODEVASF in Três Marias, Minas Gerais, under authorization from the State Forestry Institute of Minas Gerais (IEF-MG).These fish were collected in the upper São Francisco river, located in the municipality of Três Marias, in the state of Minas Gerais (18°12'32"S, 45°15'41"W) in January 2011 and January 2012.The host necropsies and parasite processing procedures followed Eiras et al. (2006).The parasitological descriptors used were those prescribed by Bush et al. (1997).Nematode measurements are presented in millimeters.The measurement ranges are presented in the results tables, and these values are followed by the means and their respective standard deviations.Morphometry was ascertained using a Nikon Alphaphot-2 microscope with a calibrated reticle coupled to the ocular lens.Parasite voucher specimens were deposited in the Helminthological Collection of the Oswaldo Cruz Institute (CHIOC), state of Rio de Janeiro, Brazil.A numbering system was used, as indicated in the results (Table 1).The host voucher specimen was deposited in the Fish of the Museum, University of São Paulo (MZUSP, 95161), state of São Paulo, Brazil.

Results and Discussion
The parasite fauna of A. fasciatus consisted of eleven nematode species, which are presented in Table 1 with their respective parasitic indeces.Nine species were represented by larval specimens and had characterized A. fasciatus as a noteworthy intermediate host in their parasitic cycles.Five species (Brevimulticaecum sp., Contracaecum sp., Cystidicoloides sp., Hysterothylacium sp. and Spiroxys sp.) out of these nine in the larval stage presented prevalence higher than 10%.Two nematode species were represented by adult specimens: Spinitectus rodolphiheringi Vaz & Pereira, 1934 and P. saofranciscencis.For these A. fasciatus was characterized as the definitive host.The prevalence of P. saofranciscencis was higher than 10%.
Differing from our study, Santos & Moravec (2009) and Martins & Yoshitoshi (2003) found high prevalences of adults and larvae in the species G. spinulosa (90%) and G. leporini (65%), respectively.Massive presence of these species gives rise to attacks mainly on the stomach, causing gross lesions and high mortality among the fish.
With regard to S. rodolphiheringi, one male, one female, and one juvenile were found in A. fasciatus.Their measurements and features were in line with what was reported by Moravec (1998).
In the São Francisco river, adult specimens of S. rodolphiheringi were found in Franciscodoras marmoratus (Reinhardt, 1874) (SANTOS & BRASIL-SATO, 2004).Thus, the presence of adult specimens of S. rodolphiheringi in A. fasciatus increases the list of known hosts in the São Francisco basin.
In this study, the features of P. saofranciscencis specimens in A. fasciatus, as well as their measurements, were equivalent to what was presented by Moravec (1998).Procamallanus saofranciscencis was identified in fish of the families Characidae (VICENTE & PINTO, 1999) and Acestrorhynchidae (MOREIRA et al., 1994) in the upper São Francisco river.Larval specimens of Procamallanus sp., which had already been identified in this basin, have also been found in Characidae (VICENTE & PINTO, 1999) and Pimelodidae (BRASIL- SATO & SANTOS, 2005).Based on the presence of the larval specimens (Procamallanus sp.) and adults of P. saofranciscencis in A. fasciatus, it can be seen that this foraging fish takes part in the cycle of these species as intermediate and definitive hosts, respectively, and this enlarges the list of hosts for this nematode group in the São Francisco basin.
Larval specimens of Cystidicoloides sp. had already been found in Leporinus friderici (Bloch, 1794) in the upper Paraná river by Takemoto et al. (2009).Thus, A. fasciatus is a new host and enlarges the list of the known intermediate hosts of Cystidicoloides sp. in the São Francisco basin.
In this study, larval specimens of Rhabdochona sp. were also found in A. fasciatus.They had previously been found in C. conirostris by Brasil-Sato & Santos (2005).The results obtained in A. fasciatus in this study indicate that foraging fish play a role as intermediate hosts for some species of Rhabdochona Railliet, 1916, thus enlarging the list of hosts in the upper São Francisco river.
Larval specimens of Spiroxys sp. were identified in A. fasciatus in Mexico (Moravec, 1998).In the upper São Francisco river, Santos et al. (2009) and Santos-Clapp & Brasil-Sato (2014) reported occurrences of these larvae in the carnivorous fish Cichla kelberi Kulander & Ferreira, 2006).In the present study, these larvae were also found in A. fasciatus, thus showing that this fish acts as an intermediate host for these parasites.
The occurrences of larval specimens of Hysterothylacium sp., Eustrongylides sp. and Goezia sp. in A. fasciatus enlarges the list of hosts in the São Francisco river, especially given that occurrences of these species had already been identified in several families of fish in the upper São Francisco river (BRASIL-SATO, 2003; SANTOS-CLAPP & BRASIL-SATO, 2014).
Larvae of Brevimulticaecum sp. were first described in fish by Moravec et al. (1997), but Bruce et al. (1994) asserted that fish rarely act as intermediate hosts for Brevimulticaecum sp.According to Moravec (1998), amphibians are intermediate hosts for Brevimulticaecum spp.and, as Bruce et al. (1994) stated, the most common definitive hosts are reptiles.In the Neotropical region

Conclusion
This study highlights occurrences of and quantitative data on eleven species of parasitic nematodes of A. fasciatus in the São Francisco river.The most prevalent species characterizing the nematodes fauna of A. fasciatus were, in larval form, Hysterothylacium sp. and Contracaecum sp., followed by Spiroxys sp., Cystidicoloides sp., and Brevimulticaecum sp; and, in adult form, P. saofranciscencis.Except for Contracaecum sp. and P. saofranciscencis, A. fasciatus represents a new host for these nematode species.These results aid in elucidating the biodiversity of parasites in fish in the Neotropical region; they also add to research projects under development in the São Francisco basin.

Table 1 .
Prevalence (%), mean intensity (MI), mean abundance (MA), and their respective standard deviations (SD), followed by amplitude (A), importance of values (IV), and site of infection for nematodes found in Astyanax fasciatus (Cuvier, 1819) of the upper São Francisco river, State of Minas Gerais, Brazil.

Table 2 .
Morphometry of the larval specimens of the Contracaecum sp., Hysterothylacium sp., and Brevimulticaecum sp. in Astyanax fasciatus (Cuvier, 1819) of the upper São Francisco river, State of Minas Gerais, Brazil.
X = mean; SD = standard deviation; Min. and Max.= minimum and maximum values for the measurement.Characters: L = length; W = width; -lacks; *not measured.