Are similar the parasite communities structure of Trachelyopterus coriaceus and Trachelyopterus galeatus ( Siluriformes : Auchenipteridae ) in the Amazon basin ?

The aim of this study was to compare the parasite communities in two sympatric host populations, Trachelyopterus coriaceus and Trachelyopterus galeatus, which were caught in tributary of the Amazon River in Brazil. All the specimens of T. galeatus and T. coriaceus were infected by one or more parasites, such as Ichthyophthirius multifiliis, Tripartiella tetramerii, Trichodina nobilis, Cosmetocleithrum striatuli, Contracaecum sp., Cystidicoloides sp., Dadaytremoides parauchenipteri and Gorytocephalus spectabilis. Seven species were common to both host fish, and there were 1-5 parasite species per host. In both hosts, trichodinids were dominant. Aggregate dispersion of ectoparasites and endoparasites was observed, with greater aggregation among endoparasites. Only the ectoparasites species showed differences in intensity and/or abundance. However, the parasite communities of the two hosts were taxonomically similar (99%) and characterized by high prevalence and high abundance of ectoparasites, but with low diversity, prevalence and abundance of endoparasites. Trachelyopterus galeatus, the host with the larger body size, presented greater variation of Brillouin diversity and evenness, while T. coriaceus had higher Berger-Parker dominance values and total numbers of parasites. This first study on these parasites of T. galeatus and T. coriaceus showed that the life mode, size of the hosts and the availability of infective forms of the parasites were the main factors that influenced the parasite communities structure.


Introduction
Auchenipteridae are Siluriformes with around 21 genera and 64 species distributed in freshwater rivers in South America, from Argentina to Panamá (BURGESS, 1989;FROESE & PAULY, 2015).Most of these species have crepuscular or nocturnal habits, swimming frenetically close to the water surface in search of insects or other food items.During the daytime, they remain hidden in crevices or holes, or under tree trunks and branches.Trachelyopterus coriaceus Valenciennes, 1840, and Trachelyopterus galeatus Linnaeus, 1766, are congeneric phylogenetically related Auchenipteridae (BIRINDELLI, 2014) of small size that reach a maximum of 22 cm, and reach sexual maturity at a length of around 11 cm.Both of these fish species are found in wet areas of floodplains, and thus, T. galeatus and T. coriaceus are adapted to these hypoxic environments.The diet of Trachelyopterus spp.generally consists of insects, rotifers, mollusks and crustaceans (ANDRADE-LÓPEZ & MACHADO-ALLISON, 2009;MESQUITA et al., 2011;FROESE & PAULY, 2015).These two species of Trachelyopterus are not listed by the IUCN as endangered.Therefore, do these two siluriforms Auchenipteridae of the Amazon basin of Brazil have similar parasite communities structure?
The Igarapé Fortaleza basin is a singular ecosystem that is located in the eastern Amazon region of northern Brazil, and is an ecosystem highly influenced by the Amazon River system.It consists of linked fluvial physical systems that provide freshwater drainage, and is influenced by the high rainfall of the Amazon region and the daily tides of the Amazon River (GAMA & HALBOTH, 2004;TAVARES-DIAS et al., 2013;BITTENCOURT et al., 2014a).The waters that periodically spread out across the floodplain are rich in nutrients, because of the rapid decomposition of grasses, animal remains and the humus layer of the forest.This leads to growth of new vegetation (Poaceae, Cyperaceae, Fabaceae, Onagraceae, Araceae, Asteraceae, Convolvulaceae and Lentibulariaceae) and invertebrate biomass (insects, zooplanktonic crustaceans and mollusks), which are used as food by fish (GAMA & HALBOTH, 2004;TAKIYAMA et al., 2012), such as by T. galeatus and T. coriaceus.This ecosystem has been strongly influenced by eutrophication due to urbanization, as observed with regard to the parasite community of Curimata cyprinoides Linnaeus, 1766 (TAVARES-DIAS et al., 2013).Moreover, the Igarapé Fortaleza basin suffers a strong influence of invasion from Oreochromis niloticus, an exotic fish in Brazil (BITTENCOURT et al., 2014a).However, studies on parasite communities of T. galeatus and T. coriaceus has been not addressed.
In populations of wild fish, ectoparasites and endoparasites of different taxonomic groups can generally be found (LUNASCHI, 1989;TAKEMOTO & LIZAMA, 2009;KOHN et al., 2011;MESQUITA et al., 2011;NEVES et al., 2013;TAVARES-DIAS et al., 2013).The possibility of obtaining numerous repeats and quantifying the entirety of the parasite population distributed in different infection sites in fish facilitates detection of patterns within population dynamics, interspecies relationships and feeding relationships.These may reveal the potential that fish could have for participating as intermediate, paratenic or definitive hosts in the ecological systems of endohelminths (TAKEMOTO & LIZAMA, 2009;MESQUITA et al., 2011;TAVARES-DIAS et al., 2013).However, the parasite community structure may be influenced by the environmental and a variety of other factors that relate mainly to the ecology and physiology of the host, seasonality, habitat quality and presence of larval stages of parasites in invertebrate transmitters (TAKEMOTO & LIZAMA, 2009;KOHN et al., 2011;NEVES et al., 2013;TAVARES-DIAS et al., 2013).
In wild populations of T. galeatus of the Brazil, only the following helminths such 2 species of digeneans, 3 nematodes and 1 cestode are known (PAVANELLI & SANTOS, 1990;FERNANDES & KOHN, 2001;DIAS et al., 2006;TAKEMOTO & LIZAMA, 2009;KOHN et al., 2011).In wild populations of T. galeatus of the Argentina, there have been reports only 2 species digeneans (LUNASCHI, 1989;LUNASCHI & SUTTON, 1995).However, the parasite communities that T. galeatus and T. coriaceus harbor are still unknown and there are also no studies on their structure.In addition, given that these congeneric hosts present similar biological and behavioral characteristics and are phylogenetically close, this may favor the presence of similar parasite communities (GONZÁLEZ & OLIVA, 2006;ALARCOS & TIMI, 2012).Thus, the present study compared the parasite communities, prevalence, intensity, abundance and parasite-host interactions of T. galeatus and T. coriaceus living in sympatry in a tributary of the Amazon River system, northern Brazil.

Fish and capture location
Between September and December 2012, 37 specimens of T. galeatus and 35 specimens of T. coriaceus were caught in the Igarapé Fortaleza basin, tributary of the Amazon River system in the municipality of Macapá (state of Amapá), in northern Brazil, for parasitological analyses.All the fish were caught using hand nets and gillnets (15 to 25 mm) and were transported alive to the Laboratory for Aquatic Organism Health at Embrapa Amapá (Macapá), for necropsy.This study was developed in accordance with the principles adopted by the Brazilian College of Animal Experimentation (Cobea).

Parasites collection and analysis procedures
The fish were weighed (g) and their lengths were measured (cm).Following this, the gills and gastrointestinal tract were examined to ascertain whether any protozoan and metazoan parasites were present.All the parasites were collected, fixed, conserved, quantified and stained for identification (EIRAS et al., 2006).The ecological terms used were those recommended by Rohde et al. (1995) andBush et al. (1997).Voucher specimens were deposited at the Scientific and Technological Research Institute of the State of Amapá (IEPA), in the Scientific Collection Curation Office for the Fauna of Amapá (CCFA), under accession number IEPA 033-043-P.
The Brillouin diversity index (HB), richness of parasite species, evenness (E) and Berger-Parker dominance index (d) were calculated for each parasite infracommunity (MAGURRAN, 2004), using the Diversity software (Pisces Conservation Ltd, UK).The dispersion index (ID) and discrepancy index (D) were calculated using the Quantitative Parasitology 3.0 software, in order to detect the distribution pattern of the parasite infracommunities (RÓZSA et al., 2000), for species with prevalence > 10%.The significance of the ID, for each infracommunity, was tested using the d-statistic (LUDWIG & REYNOLDS, 1988).Similarity in parasite communities between host populations was compared using the Jaccard index and Morisita index (LUDWIG & REYNOLDS, 1988;MAGURRAN, 2004).Both similarity indices were calculated using the Past software (Paleontological Statistics version 3.0).
Body weight (g) and total length (cm) were used to calculate the relative condition factor (Kn) of the fish using the length-weight relationship (W = aL b ) after logarithmic transformation of length and weight and subsequent adjustment of two straight lines, thus obtaining lny = lnA + Blnx (LE-CREN, 1951).

Data analyses
To compare prevalence between T. galeatus and T. coriaceus, the chi-square test (χ 2 ) was used, followed by the Yates correction.The intensity, abundance, species richness, diversity (HB), evenness (E) and dominance (d) were compared between the two hosts using the Mann-Whitney test (U).The Shapiro-Wilk test was used to determine whether parasite abundance data followed a normal distribution pattern.Spearman's correlation coefficient (rs) was used to determine possible correlations of the total length and body weight with parasites abundance, the Brillouin index (HB) and the richness of parasite species (ZAR, 2010).
Principal component analysis (PCA) was carried out to compare the ways in which body and diversity influenced the parasite communities of T. galeatus and T. coriaceus.This analysis was performed using the Past software (Paleontological Statistics, version 3.0).
The parasite species in T. galeatus and T. coriaceus presented an aggregated distribution pattern (Table 2), which is a common pattern for freshwater fish.
In T. coriaceus, the abundance of T. tetramerii, T. nobilis and C. striatuli showed a negative correlation with host length.In T. galeatus, the abundance of Tripartiella tetramerii presented a positive correlation with host length and weight, while the abundance of C. striatuli presented a negative correlation with host length (Table 4).
Principal component analysis based on the hosts' body and diversity parameters showed that for Brillouin diversity, evenness, species richness of parasites and Berger-Parker dominance were the main factor correlated with T. coriaceus and T. galeatus.
Table 3. Mean diversity indexes and body parameters ± standard deviation and ranges (in parentheses) for the parasites community in Auchenipteridae species in the Amazon River system (Brazil).U: Mann-Whitney.The cumulative variance explained by the variables used was 83.9% for both axes (Figure 2).The Jaccard index (J = 0.86) and Morisita index (Cλ = 0.99) demonstrated similarity between the parasite communities of T. coriaceus and T. galeatus.The multivariate analysis based on the component community of the parasites of T. coriaceus and T. galeatus allowed observing that there is no separation among these hosts and only I. multifiliis was the species with least importance in this analysis (Figure 3).

Parameters
For T. galeatus, the equation for the weight-length relationship was Wt = 0.0034Lt 3.5798 (r 2 = 0.952); and for T. coriaceus, it was Wt = 0.0091Lt 3.1295 (r 2 = 0.890).Thus, both of these relationships Table 4. Spearman's correlation coefficient (rs) for the abundance of parasites, in relation to the total length (cm) and body mass (g) for species of Auchenipteridae in the Amazon river system (Brazil).

Hosts
Trachelyopterus galeatus (N = 37)   Parasites of Trachelyopterus were therefore allometrically positive, which indicates that there was greater increase in size than in body weight.
This first study on the parasitic fauna of T. coriaceus and T. galeatus showed that they had similar richness of species and component community.Body size, diversity and evenness were greater for T. galeatus, but body size did not influence the diversity and richness of parasite species, in either of the two hosts.In these two hosts in the Amazon region, the dominant species were T. tetramerii and Trichodina nobilis, followed by I. multifiliis.These protozoans are typical of lentic-eutrophized environments like the hydrographic basin of this study (TAVARES-DIAS et al., 2013, 2014;BITTENCOURT et al., 2014b).In addition, in T. coriaceus and T. galeatus, the greatest richness of parasites was in species of helminths, with predominance of endoparasites of relatively high prevalence and low abundance, but only two endoparasites were found in larval stage (Contracaecum sp. and Cystidicoloides sp.).Several variables may influence the presence of endoparasites species, especially exposure to infective forms, which are directly acquired through the hosts' feeding (MOREIRA et al., 2009;TAKEMOTO & LIZAMA, 2009;MESQUITA et al., 2011;TAVARES-DIAS et al., 2013).It is well known that the diet of the fish can be deduced from trophically transmitted parasites and because most endoparasites are associated with a specific ecological niche and diet, high diversity in host parasite fauna is often a result of a diverse host diet.Hence, a diverse parasitic communities of trophically transmitted parasites may indicate that the host population consumed a diversity of prey in habitat (WILSON & HUBSCHMAN, 1985;MORAVEC, 2007;TARASCHEWSKI, 2008;MOREIRA et al., 2009;MORAVEC, 2009;NEVES et al., 2013;TAVARES-DIAS et al., 2013;BITTENCOURT et al., 2014b;TAVARES-DIAS et al., 2014).
The ectoparasites and endoparasites of T. coriaceus and T. galeatus presented aggregated dispersion, but endoparasites infections were the more aggregated.Aggregated dispersion patterns for ectoparasites and endoparasites have also been described in other freshwater hosts (MESQUITA et al., 2011;TAVARES-DIAS et al., 2014;AMARANTE et al., 2015), and these have been attributed to factors relating to the hosts, parasites and environment.These factors include formation of schools of fish, taxon in relation to sex, habitat, presence of parasite larvae, feeding habits and length of the hosts and the genetic and immune heterogeneity of the hosts (ROHDE et al., 1995;TAVARES-DIAS et al., 2014;AMARANTE et al., 2015).
The levels of infection due to I. multifiliis in T. coriaceus and T. galeatus were similar.This ectoparasite ciliate, which does not have parasitic specificity, occurs more frequently in fish in farmed environments, influenced by factors related to the parasite and host, and also by the physical and chemical characteristics of the water, such as dissolved oxygen levels, pH, hardness, alkalinity and temperature (WEI et al., 2013;FORWOOD et al., 2015).However, this protozoon has wide geographic distribution and can parasitize fish on all continents.Severe infections may also cause mortality in populations of wild fish, because I. multifiliis has the capacity to reproduce rapidly (RAISSY et al., 2010;FORWOOD et al., 2015), when the environmental conditions are favorable.This was the first record of I. multifiliis for T. coriaceus and T. galeatus.
In T. coriaceus and T. galeatus, the prevalence of T. tetramerii and T. nobilis was similar for both hosts, but the intensity and abundance were higher in T. coriaceus.Moreover, the abundance of these trichodinids was higher in individuals of T. galeatus of greater size and was lower in individuals of T. coriaceus of greater length.In populations of wild fish, infections due to species of trichodinids are more frequent in environments that are eutrophized and have low oxygen levels (BASSON & VAN AS, 2002;TAVARES-DIAS et al., 2014), like the Igarapé Fortaleza basin.This was the first record of T. tetramerii and T. nobilis for T. coriaceus and T. galeatus.
Cosmetocleithrum striatuli, a monogenoidean originally described in Trachelyopterus striatulus Steindachner, 1877, in the Guandu River, Southern Brazil region (ABDALLAH et al., 2012;SILVEIRA et al., 2013), showed a higher level of infection in adults of T. coriaceus than in subadults of T. galeatus, in the present study.These differences occurred because smaller and therefore younger individuals of T. coriaceus were more parasitized.In T. coriaceus, the abundance of C. striatuli showed a negative correlation with host length, while in T. galeatus the correlation was weak.These distinct results were due to differences in the host size.Thus, since C. striatuli was previously only known in T. striatulus (COHEN et al., 2013), the present paper provides the first report of this monogenoidean for T. galeatus and T. coriaceus.
Gorytocephalus spectabilis only parasitized T. coriaceus, and at low infection levels, which were similar to those reported for Aquidens tetramerus Heckel, 1840; Heros efasciatus Heckel, 1840; Chaetobranchus flavescens Heckel, 1840; and Satanoperca jurupari Heckel, 1840 -all these hosts were also from the ecosystem of this study (BITTENCOURT et al., 2014b;TAVARES-DIAS et al., 2014).Although congeneric host species have similar biological and behavioral characteristics and are therefore potential hosts for parasitic fauna that is also similar, closely related species may also exhibit divergent characteristics that allow them to coexist, such as in relation to some trophic traits (GUIDELLI et al., 2009).The absence of G. spectabilis in T. galeatus in this study indicates that despite the overlapping of living, feeding and environmental habits, this host did not have any contact with the infective forms of this endohelminth through trophic means.Species of Neoechinorhynchidae in freshwater fish have life cycles involving a definitive host and an intermediate host, which may be arthropods (amphipods, ostracods, isopods or copepods).However, some species have fish species as paratenic or definitive host, when they ingest an invertebrate that is an intermediate host or a small fish that serves as a paratenic host (WILSON & HUBSCHMAN, 1985;TARASCHEWSKI, 2008).Despite the low abundance of G. spectabilis in T. coriaceus and T. galeatus, these fish seem to be definitive hosts in the environment studied here.This was the first record of G. spectabilis for T. coriaceus and T. galeatus.
Trachelyopterus coriaceus and T. galeatus showed similar low levels of infection by larvae of Contracaecum sp.These larvae are anisakid with parasitic specificity and, during their larval stage; their primary hosts are microcrustaceans (MORAVEC, 2009;MOREIRA et al., 2009).In the adult phase, piscivorous birds are their definitive hosts and fish are paratenic hosts (MORAVEC, 2009).The levels of infection due to larvae of Cystidicoloides sp. were higher in T. galeatus than in T. coriaceus, thus indicating that T. galeatus had greater contact with the infective forms of this endohelminth.In Brazil, only Cystidicoloides fischeri Travassos, Artigas andPereira, 1928, andCystidicoloides izecksohni Fabio, 1982, are known to parasitize different species of fish (LUQUE et al., 2011).For Cystidicolidae, species of crustaceans are the intermediate hosts and fish are paratenic or definitive hosts during their life cycle.However, the adult forms of these parasites occur in adult piscivorous fish, which are the definitive hosts (MORAVEC, 2007).Therefore, the presence of larvae of Cystidicoloides sp.indicates that adults of T. coriaceus and subadults of T. galeatus are paratenic hosts for this nematode in the ecosystem of this study.
Dadaytremoides parauchenipteri, a digenean that was originally described in T. galeatus from Argentina (LUNASCHI, 1989), showed similar levels of infection for T. coriaceus and T. galeatus in the present study.This species of Cladorchiidae had not previously been reported as parasitizing other species of fish in South America (KOHN et al., 2007) and therefore this was the first record of D. parauchenipteri in Brazil.Moreover, this endoparasite seems to have wide geographic distribution and primary association with species of siluriform Auchenipteridae.Although the life history of D. parauchenipteri is unknown, Thatcher & Jégu (1996) stated that species of Cladorchiidae have a life cycle in which cercariae are released from infected snails and, through encysting on aquatic vegetation, form metacercariae that are then consumed by host fish.Given that in the ecosystem of this study, T. coriaceus and T. galeatus live close to aquatic vegetation; this favors encounters between these hosts and metacercariae, i.e. the infective forms of D. parauchenipteri.Therefore, T. coriaceus and T. galeatus are definitive hosts for this endohelminth, in the environment investigated here.
In summary, the richness of endoparasites with a complex life cycle in T. coriaceus and T. galeatus indicates that in the environment that these fish inhabit, their diet consists mainly of molluskand crustacean species.The size and behavior of these hosts, richness of parasites and availability of infective forms of intermediate hosts that make up the diet of these Siluriformes were the main factors influencing similar parasite communities.The parasite communities of these Amazonian hosts were characterized by high prevalence and high abundance of ectoparasites, but with low diversity, prevalence and abundance of endoparasites.Furthermore, the phylogenetic and taxonomic proximity of the hosts was also a strong influence on the parasite species, once the parasite communities of these two hosts were taxonomically similar (99%).Finally, the external and internal host environment influenced the few differences in prevalence, intensity and abundance of parasites.

Figure 1 .
Figure1.Species richness of parasites for species of Auchenipteridae in the Amazon River system (Brazil).

Figure 2 .
Figure 2. Scatterplot scores from the principal component analysis (PCA) on factors influencing the parasites component communities of Trachelyopterus galeatus (○) and Trachelyopterus coriaceus (•) in the Amazon River system (Brazil).

Table 1 .
Parasites of two Auchenipteridae fish in a tributary in the Amazon River system (Brazil).
P = Prevalence; MI = Mean intensity; SD = Standard deviation; MA = Mean abundance; FD = Frequency of dominance; SI = Site of infection.

Table 2 .
Index of dispersion (ID), d-statistic, discrepancy index (D) and frequency of dominance (FD) for the infracommunities of parasites in species of Auchenipteridae in the Amazon River system (Brazil).