Diversity of monogenean parasites on gills of fishes from the Matapi River, in the Brazilian Amazon.

This study investigated the fauna of monogeneans on gills of 13 fish species from the Matapi River, Brazilian Amazon. A total 548 fish belonging to 13 species (1 Anostomidae, 3 Characidae, 1 Curimatidae, 1 Hemiodontidae, 2 Serrasalmidae, 3 Scianidae, 1 Ageneiosidae and 1 Tetradontidae) were examined. From these fish, 6 species were infected and with a total prevalence of 22.4%. Monogeneans collected are represented by the following taxa: Anacanthorus gravihamulatus, Notozothecium minor, Notozothecium penetrarum, Diplectanum piscinarius, Aetheolabes goeldiensis, Euryhaliotrema succedanus, Anacanthorus jegui, Urocleidoides astyanacis, Urocleidoides strombicirrus, Euryhaliotrema sp. and Urocleidoides spp. There was a variation in the prevalence, mean intensity and mean abundance of monogeneans among the host populations examined. Monogeneans of Metynnis lippincottianus, Plagioscion squamosissimus, Astyanax bimaculatus and Curimata incompta presented a highly aggregated dispersion pattern. Body weight of M. lippincottianus and C. incompta presented a weak positive correlation with abundance of parasites. Lastly, this is first study for 12 fish species from the Matapi River and the first report of E. succedanus for Plagioscion surinamensis and N. penetrarum for Serrasalmus rhombeus.


Introduction
The Amazon River system has a high diversity and richness of fish species, representing the 7% of fish species form the planet. This richness and diversity are related to the various environmental characteristics of this basin, such as the seasonal variation in water level, pH, temperature, transparency, aquatic productivity, complexity of biotopes (lakes, rivers and streams), habitats (aquatic macrophytes and flooded forest), as well as other aspects directly related to its geology (Leal et al., 2018). In addition, this large hydrographic basin is formed by several tributaries of different size and importance for fishing activities that generates food and income for many riverine populations, as for example the Matapi River basin (Silva et al., 2016;Sousa et al., 2019).
The Matapi River is born in the central region of the state of Amapá (Brazil), flowing into the Amazon River, near the municipality of Santana. Its main tributaries are the Flexal and Pirativa rivers, and the Maruanum and Lago streams. This basin is influenced by daily floods from the tides of the Amazon River and is therefore influenced by the discharges from the Amazon River. These tides considerably affect the hydrodynamics of inundated forest and floodplain areas in the Matapi River basin (Santos et al., 2004;Silva et al., 2016;Sousa et al., 2019) and consequently, the life history of 104 species of fish known for this basin, among Characiformes, Cichliformes, Siluriformes, Clupeiformes, Tetraodontiformes, Gymnotiformes and Beloniformes. Among these families, Serrasalmidae, Characidae and Cichlidae are the most predominant (Silva et al., 2016). Despite this diversity of the ichthyofauna, there are only reports of monogeneans in the following cichlids: Geophagus camopiensis (Pellegrin, 1903), Pterophyllum scalare (Schultze, 1823), Satanoperca jurupari (Heckel, 1840) and Satanoperca acuticeps (Heckel, 1840) (Ferreira-Sobrinho & Tavares-Dias, 2016) and Hemibrycon surinamensis (Géry, 1962) (Sousa et al., 2019).
Monogenea (Van Beneden, 1858) are, in general, ectoparasites that mainly infect fish species, and have a simple and direct cycle and, consequently, may present a high reproduction rate in these hosts (Lapera et al., 2017). Some biotic factors influence the diversity and infection levels of monogeneans in fish, including the behavior, migratory habits, size, age, and sex of the hosts. Abiotic factors such as pollution, low dissolved oxygen, pH, water temperature and seasonality are also important for the levels of monogenean infection (Dogiel, 1961;Lizama et al., 2008;Vital et al., 2011, Takemoto et al., 2013Tavares-Dias et al., 2014Ferreira-Sobrinho & Tavares-Dias, 2016). Therefore, the diversity and infection levels by monogeneans can vary between the different species of fish (Whittington & Chisholm, 2008;Cohen et al., 2013), influenced by several factors. However, as the diversity of monogeneans in fish from the Matapi River is little known, the aim of this study was to investigate the fauna of these ectoparasites in the gills of 13 fish species of this basin.

Fish collection procedures
Bimonthly, between March 2012 and August 2013, 13 species of fish were collected in the Matapi River (Table 1), in the municipality of Santana, state of Amapá, Brazil (Figure 1), for analysis of monogeneans in the gills. Fish were collected using gill nets of various mesh sizes (20,25,30,35,40 and 70 mm between knots), matapi traps, casting nets, hand lines and longlines, and the mean duration of fishing effort was 8 h. Gills were collected and fixed in formalin (5%) and transported to Laboratory of Aquaculture and Fishery of Embrapa Amapá, in Macapá (Brazil).
During fish collection, water temperature, electrical conductivity and pH were measured using a multiparameter analyzer (Horiba, model W23-XD). A Secchi disk was used to determine the transparency. The suspended solids analysis was performed using the gravimetric method and membrane filtration. Rainfall data were obtained from the Hydrometeorology and Renewable Energy Center (NHMET) of the Institute of Scientific and Technological Research of the State of Amapá (IEPA). The temperature was 27.5 ± 1.5 °C, pH 5.5 ± 0.7, electrical conductivity 2.8 ± 1.9 µS/cm, suspended solids 25.0 ± 29.5, transparency 85.0 ± 57.3 cm and rainfall 219.4 ±120.0 mm. Maximum temperature and precipitation occurred of June to December and minimum temperature and precipitation occurred of January to May.
The present study was conducted in accordance with the recommendations of the Brazilian College for Animal Experimentation and with authorization from the Ethics Committee for Use of Animals of Embrapa Amapá (Protocol N o 014 -CEUA/CPAFAP).

Parasite collection and analysis procedures
Each fish was weighed (g), measured for total length (cm), and analyzed for the presence of monogeneans. The gills were removed and analyzed using a stereomicroscope. The monogeneans found were preserved in ethyl alcohol (70%). The techniques used to count and prepare the parasites for identification were those previously recommended by Eiras et al. (2006). The ecological terms used were those recommended by Bush et al. (1997).
In order to detect the distribution pattern of the parasite infracommunities (Rózsa et al., 2000), the index of dispersion (ID) and the Poulin discrepancy index (D) were calculated using the Quantitative Parasitology 3.0 software for species with prevalence >10%. The ID significance for each infracommunity was tested using the d-statistic (Ludwig & Reynolds, 1988).
Differences in parasite prevalence between host species were evaluated using the G test. The correlation between the parasite abundance with length and weight of hosts was estimated using the Spearman correlation coefficient (Zar, 2010).

Results
Thirteen fish species were caught and a total of 548 specimens were examined. The total prevalence of monogeneans was 22.4%, and Metynnis lippiconttianus, Curimata incompta and Astyanax bimaculatus were the more abundant fish species (Table 1).
From the 13 species of fish examined, six species were infected by one or more species of monogeneans, such as: There was a variation in the prevalence, mean intensity and mean abundance of monogeneans among the host populations examined ( Table 2) There was no correlation between the abundance of monogeneans and the length (rs = -0.203, p = 0.152) and weight (rs = -0.187, p = 0.188) of P. squamosissimus. A weak positive correlation between the abundance of monogeneans and the length (rs = 0.293, p = 0.0006) was found, but there was no correlation with the weight (rs = 0.099, p = 0.257) of C. incompta. There was a correlation between the abundance of monogeneans and the length (rs = 0.187, p = 0.078) of M. lippincottianus, but a weak positive correlation between the abundance of monogeneans and the weight (rs = 0.204, p = 0.05) was observed. For A. bimaculatus, there was a correlation between the abundance of monogeneans and the length (rs = -0.033, p = 0.781) and weight (rs = 0.041, p = 0.439) of hosts.
In fish populations, sometimes the parasite abundance is correlated with body size of the host population, but this correlation may also be weak or non-existent due to several factors, for example, small variation in host size, small sampling, etc. (Lizama et al., 2008;Hoshino & Tavares-Dias, 2014;Tavares-Dias et al., 2014Neves et al., 2016;Oliveira & Tavares-Dias, 2016;Lapera et al., 2017;Gallegos-Navarro et al., 2018). In M. lippincottianus from the Matapi River, the abundance of A. jegui had a weak positive correlation with body weight of this host. The abundance of Urocleidoides spp. also showed a weak positive correlation with the length of C. incompta. Similar finding was reported by Neves et al. (2016) for this same host from the Igarapé Fortaleza basin, in State of Amapá. Therefore, weight or length had little influence on the monogenean community of these two hosts.
In this study, Plagioscion auratus was not infected by any monogenean species, but P. squamosissimus was infected by D. piscinarius, E. succedanus and A. goeldiensis, and P. surinamensis was infected only by E. succedanus. However, Cohen et al. (2013) listed other species of monogeneans also infecting P. squamosissimus in Brazil: Table 2. Species of Monogenea from the gills of fish species from the Matapi River, Amapá, Brazil. Diplectanum decorrum Kritsky & Thatcher, 1984;Diplectanum gymnopeus, Kritsky & Thatcher, 1984;Diplectanum pescadae, Kritsky & Thatcher, 1984;Euryhaliotrema chaoi, Kritsky and Boeger, 2002;Euryhaliotrema potamocetes, Kritsky &Boeger, 2002 andEuryhaliotrema thatcheri, Kritsky &Boeger, 2002. The infection levels of monogeneans in P. squamosissimus and P. surinamensis were similar, since they are congeneric species of hosts inhabiting the same environment. However, in P. squamosissimus from the Tietê River, where it was introduced, there was infection only by D. piscinarius (Lapera et al., 2017) and the parasitism levels were higher than in P. squamosissimus and P. surinamensis of the current study. Lapera et al. (2017) showed that infections by D. piscinarius cause lesions in the gills of P. squamosissimus, because this monogenean species can be potentially harmful to hosts.

Plagioscion squamosissimus
In M. lippincottianus, we found only A. jegui, and infection levels were lower than the reported by Hoshino & Tavares-Dias (2014), for this same host in the Igarapé Fortaleza basin. Serrasalmus rhombeus was infected by A. gravihamulatus, N. minor and N. penetrarum. Cohen et al. (2013) listed other 22 species of monogeneans infecting S. rhombeus in Brazil, of which 4 are species of Amphitthecium, 7 Anacanthorus, 3 Enallothecium, 3 Mymarothecium, 4 Notothecium and 1 Notozothecium. However, this is the first record of N. penetrarum for S. rhombeus, because this parasite was originally described in Pygocentrus nattereri Kner, 1960 from the Guaporé River, State of Rondônia, northern Brazil (Boeger & Kritsky, 1988). In addition, the infection levels of monogeneans in S. rhombeus were lower than reported for P. nattereri from the Solimões River, State of Amazonas (Vital et al., 2011).
Astyanax bimaculatus from the Matapi River was infected by U. astyanacis and U. trombicirrus, but U. astyanacis presented higher infection levels. However, infection levels by these monogeneans were higher than those observed for Urocleidoides sp., Amphitecium sp. and Notozothecium spp. in Astyanax altiparanae Garutti & Britski, 2000 from the Upper Paraná River, State of Paraná, Brazil (Lizama et al., 2008). In the present study, Curimata incompta was infected by Urocleidoides spp., a similar finding reported also for C. incompta (Neves et al., 2016) and for Curimata cyprinoides Linnaeus, 1766(Tavares-Dias et al., 2013 both hosts from the Igarapé Fortaleza basin. Despite these results, species of monogeneans that parasitize fish of the genus Curimata are still unknown (Cohen et al., 2013). In addition, infection levels by Urocleidoides spp. in C. incompta were lower than the reported for C. cyprinoides (Tavares-Dias et al., 2013) and for C. incompta from the Igarapé Fortaleza basin, an environment eutrophicated due to the urbanization of two municipalities (Tavares-Dias et al., 2013;Neves et al., 2016).

Conclusions
We found a diversity of monogenean species with distinct infection patterns in the studied fish species that may has been influenced by the host species and sampling. This is the first study for these fish species from the Matapi River, recording for the first time E. succedanus for P. surinamensis and Notozothecium penetrarum for S. rhombeus. The present study established fauna and infection data for monogeans in different fish species from Matapi River basin, an ecosystem that is subject to an increase in environmental changes due to agriculture, extensive breeding of buffalo in the várzea forests, urbanization and industrialization. Thus, these data will be used for comparisons in future studies regarding environmental impacts from anthropogenic actions in this basin.