Paratrygon Research Articles

Morphological, cytochemical and ultrastructural aspects of blood cells in freshwater stingray species in the middle Rio Negro basin of Amazonian Brazil

In the present work, we examined the morphology, dimensions, cytochemical staining reactions and ultrastructure of blood cells from three freshwater stingray species, Potamotrygon wallacei, Potamotrygon motoro and Paratrygon aiereba, living in the waters of the middle Rio Negro basin (Barcelos, Amazonas, Brazil). We identified erythrocytes, erythroblasts, thrombocytes and four types of leukocytes (basophils, heterophils, lymphocytes and monocytes) in the blood of these stingray species. In all the freshwater stingray species studied, the shapes and dimensions of these cells were similar to those of marine elasmobranchs. Positive PAS staining occurred in heterophils and thrombocytes, and weak staining occurred in lymphocytes and monocytes, while metachromasia only occurred in basophils. Positive Sudan Black B staining was observed in thrombocytes and lymphocytes, and weak staining occurred in heterophils. Basophils and heterophils were the only cells with positive bromophenol blue staining, while no peroxidase staining was observed in any of the four leukocyte types. This is the first study to establish the dimensions and cytochemical staining profiles of blood cells in Amazonian stingray species. Because these elasmobranch species are exported as ornamental fish to countries worldwide, this study can contribute to establishing standards for blood constituents that may be helpful in assessing the health and welfare of these fish in artificial systems.

Mitochondrial DNA suggests Hybridization in Freshwater Stingrays Potamotrygon (POTAMOTRYGONIDAE: MYLIOBATIFORMES) from the Xingu river, Amazonia and reveals speciation in Paratrygon aireba

Abstract In the Xingu river basin, Brazil, occurs two genera of Potamotrygonidae family: Potamotrygon and Paratrygon. In this region, the taxa have significant economic importance for the ornamental fishing industry, being intensively captured, especially the species Potamotrygon leopoldi, which is endemic to this basin. In the attempt to propose a species-specific DNA marker for the species from Xingu, as well as ensuring a robust and reliable molecular identification, the present work analysed mitochondrial gene portions Cytochrome Oxidase C – subunit I (COI) and Cytochrome B (Cytb) of five species: P. leopoldi; Potamotrygon orbignyi; Potamotrygon motoro; Potamotrygon scobina and Paratrygon aiereba. We found haplotype sharing, with a total absence of reciprocal monophyly in the majority of taxa. Individuals morphologically identified as a species showed mitochondrial DNA from another, suggesting the first record of hybridization amongst freshwater stingrays of Xingu. Also, we detected a deep divergence among Paratrygon aiereba haplotypes, indicative of speciation, suggesting the possibility of a new species for the Xingu river. Therefore, although the is still confusing and controversial taxonomy of freshwater stingrays, and evidencing hybridization processes that may have shaped the evolutionary history of this Family, the genes COI and Cytb can successfully help in the their species identification.

Two new species of freshwater stingrays of the genus Paratrygon (Chondrichthyes: Potamotrygonidae) from the Orinoco basin, with comments on the taxonomy of Paratrygon aiereba

Abstract The genus Paratrygon, currently recognized as the sole monotypic genus of the family Potamotrygonidae, has a considerably greater diversity than previously indicated, including molecular studies, which supported P. aiereba (hitherto the only recognized species in the genus) as a possible species complex. Here we describe two new species of the genus that are both endemic to and sympatric in the Orinoco basin. Paratrygon aiereba, type species of the genus, is now restricted to the Amazon basin. Both new species are identified and defined through morphological characters such as coloration, dermal denticle morphology, arrangement of thorns, distribution and morphology of ventral lateral line canals, morphology of skeletal elements, and morphometrics. An extensive comparison of these characters between the new species herein described and P. aiereba is presented. Finally, a taxonomic reappraisal of P. aiereba is provided through a revision of preserved material and its original description, plus new evidence about its type-locatity, collectors, and a reconsideration of the destination of its type-specimen.

Phylogeography, genetic diversity and population structure of the freshwater stingray, Paratrygon aiereba (Müller & Henle, 1841) (Myliobatiformes: Potamotrygonidae) in the Colombian Amazon and Orinoco basins

The freshwater stingray Paratrygon aiereba have coloration, osteological and morphometric variations that could suggest the existence of more than one species in Colombia. In order to evaluate the phylogeography, population structure and genetic diversity for P. aiereba distributed in the Amazon and Orinoco basins, we amplified Cytochrome oxidase subunit 1 (COI) partial region of mitochondrial DNA (mtDNA) in 50 samples from eight different sub-basins. Our results suggest three phylogroups and a vicariance event occurred 43 million years ago proposing how Paratrygon diverged into the basins. A high population structure (ΦST = 0.692; p < 0.005) and a value of (K) of 3 were defined. A high genetic diversity within phylogroups was found: Phylogroup A (h = 0.64; π% = 2.48), Phylogroup B (h = 0.552; π% = 1.67), and Phylogroup C (h = 0.49; π% = 0.73). These results should be considered in local management plans, conservation programs and reclassification in at least Amazon and Orinoco.

Paratrygon aiereba irradiated anti-mucus serum reduce edematogenic activity induced in experimental model

Accidents by freshwater stingrays are common in northern Brazil, there is no specific therapy for high morbidity and local tissue destruction. The irradiation of venoms and toxins by ionizing radiation has been used to produce appropriate immunogens for the production of antisera. We planned to study the efficacy of stinging mucus irradiation in the production of antisera, with serum neutralization assays of edematogenic activity and quantification of cytokines performed in animal models of immunization with native and irradiated mucus of Paratrygon aiereba, a large freshwater stingray. Antiserum potency and its cross-reactivity with mucus from other freshwater stingrays were detected by ELISA. Immunization models demonstrated the ability to stimulate a strong humoral response with elevated levels of serum IgG detectable by ELISA, and both native and irradiated mucus were immunogenic and capable of recognizing mucus proteins from other freshwater neotropical stingrays. Mucus P. aiereba causes cellular and humoral adaptive immune responses in cells of immunized mice producing antibodies and cytokines such as TNF-α, IL-6 and IL-17. Rabbit antisera immunized with mucus from P. aiereba irradiated at 2 kGy showed a significant reduction of mucus-induced edematogenic activity in mice. Our data suggest that the use of antisera against freshwater stingray mucus show the possibility of specific therapy for these accidents.

Neuromast distribution and its relevance to feeding in Neotropical freshwater stingrays (Elasmobranchii: Potamotrygonidae)

The mechanosensory system in batoids has a unique sensory canal distribution located on both dorsal and ventral surfaces of the body. Due to the opposite position of eyes and mouth, ventral lateral-line canals are essential to detect and capture prey buried in the substrate. The present study analyzes the density of neuromasts in ventral lateral-line canals as well as their specific distribution patterns to help to understand the mechanisms involved in the foraging activities in potamotrygonid stingrays. The organization of the lateral-line canals was described in Potamotrygon albimaculata, P. jabuti and P. schroederi. Neuromasts were quantified in each canal of the ventral surface and endemic their densities were compared among P. albimaculata, P. jabuti, P. schroederi, P. wallacei, and Paratrygon aiereba. The orbito-nasal component of the infraorbital canal was examined for all genera of Potamotrygoninae to understand its origin and connection patterns. Despite similarities in the morphology of the lateral line in the examined potamotrygonid species, differences of the densities of neuromasts were observed. The distinct web-like infraorbital canal in Paratrygon aiereba held a significantly higher number of neuromasts, which apparently compensates the lower density of neuromasts along its ventral surface. The orbito-nasal component of the infraorbital canal presents connections between infraorbital and nasal canals, except for P. aiereba, which has a supra-infraorbital canals’ connection. The complex distribution of lateral line canals and their neuromasts indicate distinct sensory abilities that probably provide a high capability to detect a variety of prey in different types of substrate.

Cross-reactivity between Potamotrygon motoro antivenoms and dorsal and stinger extracts of others stingrays (Chondrichthyes: Potamotrygonidae) from the Amazon basin

In this study, two mouse hyperimmune sera were produced, one using extract from the stinger of the stingray Potamotrygon motoro and the other using extract from the dorsal region of the same species and their cross-reactivity with extracts from the following species of stingrays from the Amazon basin was investigated using Western blot and dot ELISA: Paratrygon aiereba, Plesiotrygon iwamae, Potamotrygon orbignyi and Potamotrygon schroederi. The results show that the dorsal extract was as immunogenic as the stinger extract and induced high levels of antibodies, which reacted with homologous and heterologous antigens, indicating that both types of extract may be suitable for use in the production of antivenom to treat victims of envenomation by stingrays.

The ichthyofauna in the influence area of the Lajeado reservoir, Tocantins state, Brazil

Five rivers and 13 streams in the influence area of the Lajeado reservoir (upper-middle Tocantins River) were sampled in 5 expeditions. A total of 194 fish species were recorded and with the Characiformes and Siluriformes predominant, following the observed pattern for the Neotropical region. As expected, the families with greater richness were Characidae, Loricariidae and Cichlidae. Three species listed as Endangered were collected: Mylesinus paucisquamatus Jégu &amp; Santos, 1988, Melanorivulus litteratus (Costa, 2010) and Paratrygon aiereba (Müller &amp; Henle, 1841).

Ecophysiological interactions and water-related physicochemical parameters among freshwater stingrays

The objective of this study was to compare and correlate the ecology of neonates and young individuals of Potamotrygon wallacei, Potamotrygon motoro and Paratrygon aiereba with regard to their hematological profile and the physicochemical parameters of the water that they inhabit. Principal component analysis (PCA) on the complete blood count revealed total variation of 72.92%, thus demonstrating a differentiation system for oxygen demand. On the other hand, P. motoro was considered to be an intermediate species, given that its complete blood count characteristics interacted with both P. wallacei and with P. aiereba. The interaction among the biochemical variables was shown to total 64.67% of the factors. This allowed differentiation of P. wallacei from P. aiereba, while P. motoro maintained an intermediate position. These characteristics of differentiation within the preferred environment corroborate the PCA of the present study and confirm that these species can be differentiated through considering the complete blood count and biochemical parameters. The PCA on water properties showed 68.57% differentiation, mainly comprising the x axis (49.44%). It can be affirmed that P. motoro has the capacity to inhabit the preferential areas of P. wallacei and P. aiereba, as well as occupying localities in which other stingrays are not found. In conclusion, P. wallacei presents patterns differentiating it from P. aiereba, while P. motoro is a species that presents intermediate characteristics. The latter can be considered to be a more broadly distributed species regarding its ecophysiological characteristics.

Description of two extraordinary new species of freshwater stingrays ofthe genus Potamotrygon endemic to the rio Tapajós basin, Brazil(Chondrichthyes: Potamotrygonidae), with notes on other Tapajós stingrays.

Stingrays from the rio Tapajós basin are reviewed based on material collected from its lower (i.e. from the mouth-lake to Itaituba), middle (from about the São Luiz rapids to the confluence of rios Juruena and Teles Pires), and upper (above the Juruena-Teles Pires confluence) segments. Two new species endemic to the mid and upper Tapajós, discovered long ago and common in the ornamental fish trade, are described. Potamotrygon albimaculata sp. nov. is part of the black stingray species group, and is diagnosed by its blackish brown dorsal disc color with numerous and generally evenly-spaced small whitish spots and faint ocelli, multiple rows of thorns broadly spread on dorsal and lateral tail, pelvic fins with broadly rounded apices, and two angular cartilages with the posterior far more slender but about as wide as the anterior angular. Potamotrygon jabuti sp. nov. is diagnosed by its marbled color pattern that undergoes remarkable change with growth as adults have elaborate designs of beige, golden to yellowish-orange spots or ocelli surrounded by a slender beige to golden mesh-like pattern, but neonates have simple, well-separated ocelli; this species also has a single to double row of tail thorns varying in their development, monognathic heterodonty with teeth of intermediate lateral rows of upper jaws larger and hexagonal, and two robust, more or less equally developed angular cartilages. Both species co-occur in the relatively fast-flowing mid and upper Tapajós basin, but mostly occupy different areas of the river, with P. albimaculata sp. nov. more abundant in its central troughs but foraging at its margins, whereas P. jabuti sp. nov. is also present in smaller streams over rocky, sandy and leafy substrates. The Tapajós basin includes at least seven stingray species, but additional species probably also occur. Potamotrygon motoro, P. orbignyi, P. humerosa, Potamotrygon sp., and Paratrygon aiereba are present in the lower Tapajós mouth-lake, which may also include Plesiotrygon and Heliotrygon species. In addition to the new species described herein, P. orbignyi and Paratrygon cf. aiereba occur in the mid and upper Tapajós, along with another form (Potamotrygon cf. scobina) known only from the region of the São Luiz rapids. Therefore, three additional new species may be present in the Tapajós basin, which has one of the most diverse stingray assemblages known together with the rios Negro and Tocantins-Araguaia.

Hematological parameters of three freshwater stingray species (Chondrichthyes: Potamotrygonidae) in the middle Rio Negro, Amazonas state

This paper aimed to study and compare the hematology of newborns, young, subadults, adult males, adult females and pregnant females of Potamotrygon wallacei (cururu stingray), Potamotrygon motoro and Paratrygon aiereba. Newborn cururu stingrays had lower red blood parameters than those of other development stages. Thrombograms and leukograms showed a conservative pattern between development stage, sexual dimorphism and pregnancy. In P. motoro and P. aiereba, variables relating to red blood parameters, biochemistry and leukograms showed little variation between the species' biological characteristics, thus showing that these variables are not good criteria for differentiating them within the same species. In conclusion, the development stage is an important factor for differentiating hematological properties in the cururu stingray, while this has not been observed in P. motoro and P. aiereba stingrays.

Proposal of a non-lethal visual census method to estimate freshwater stingray abundance

&lt;p&gt;There is not a current method to estimate South American freshwater stingray’s abundance. Therefore we designed a census method and tested it in the field. It consists of making nocturnal surveys by boat in large rivers (&amp;gt;25m width) and floodplain lagoons of varying sizes, along transects of 100m x 10m (1000 m2). We applied this method in the Tomo River, a tributary of the Orinoco River in Colombia. 110 transects were surveyed in 200 runs. A total of 149 rays of four species were recorded: &lt;em&gt;Potamotrygon motoro, Potamotrygon orbignyi, Potamotrygon schroederi&lt;/em&gt; and &lt;em&gt;Paratrygon aiereba. P. motoro&lt;/em&gt; was the most abundant with a density of 0.31 individuals /1000 m2 (SD=0.5). This method gave optimal results when applied to habitats with high transparency and shallow depth (&amp;lt; 1m) since it permitted the identification of both adults and juveniles present.&lt;/p&gt;

Tamanho Populacional e Uso de Habitat de Uma Assembleia de Raias de Água Doce (Potamotrygonidae) na REBIO do Parazinho (Macapá, Amapá)

The assemblage research may provide valuable information on the different ways distinct species respond to varied ecological factors. Tagging and recapturing are useful techniques used in the estimation of population parameters of populations with members that can be individually tagged and that cannot be consistently found. . The aim of this study was to investigate the patterns of the freshwater stingray population and the community population of the taxocene at the Reserva Biologica (REBIO) in Parazinho. Samples were collected every 2 months from March 2012 to January 2013 using a bottom longline with 50 hooks each and were monitored during every receding tide; a cast net, jigging, and drift net were also used. The stingrays were internally tagged with a Passive Integrated Transponder (PIT) microchip, which was inserted near the base of the tail; these stingrays were then released at the same capture site. The Jolly-Seber method was used for the estimation of population parameters for the taxocene. A total of 115 stingrays were captured, 7 of which were recaptured. These 115 stingrays comprised 8 different species classified as follows: Paratrygon aiereba, Potamotrygon motoro, Potamotrygon orbignyi, Potamotrygon scobina, Potamotrygon constellata, Potamotrygon cf. dumerilii , Potamotrygon sp., and Potamotrygon sp 1. The estimated size of the taxocene was very high, which was probably due to the active movement of the stingrays. The number of recaptures was high, and individuals were mainly recaptured from the same initial capture site. The stingrays also showed preference for areas with muddy soils. Keywords: Potamotrygon ; marking; Jolly-Seber.

Gill dimensions in near-term embryos of Amazonian freshwater stingrays (Elasmobranchii: Potamotrygonidae) and their relationship to the lifestyle and habitat of neonatal pups

This comparative study of gill morphometrics in near-term embryos of freshwater stingray potamotrygonids examines gill dimensions in relation to neonatal lifestyle and habitat. In embryos of the potamotrygonids Paratrygon aiereba, Plesiotrygon iwamae, Potamotrygon motoro, Potamotrygon orbignyi, and cururu ray Potamotrygon sp. the number and length of filaments, total gill surface area, mass-specific surface area, water-blood diffusion distance, and anatomical diffusion factor were analysed. In all potamotrygonids, the 3rd branchial arch possessed a larger respiratory surface than the other gill arches. Larger embryos had more gill surface area and large spiracles, which are necessary to maintain the high oxygen uptake needed due to their larger body size. However, the higher mass-specific gill surface area observed in near-term embryos may be advantageous because neonates can use hypoxic environments as refuges against predators, as well as catch small prey that inhabit the same environment. As expected from their benthic mode of life, freshwater stingrays are sluggish animals compared to pelagic fishes. However, based on gill respiratory morphometry (such as gill area, mass-specific gill area, the water-blood diffusion barrier, anatomical diffusion factor, and relative opening of the spiracle), subtypes of lifestyles can be observed corresponding to: active, intermediate, and sluggish species according to Gray's scale.

Comparative morphology of the juvenile skeleton in freshwater stingrays with special focus on Paratrygon aiereba (Myliobatiformes: Potamotrygonidae)

The South American freshwater stingray family Potamotrygonidae (Neoselachii: Chondrichthyes) consists of four well-established genera: Heliotrygon, Plesiotrygon, Potamotrygon and Paratrygon including numerous species of uncertain taxonomic status. Here, we present a detailed description and analysis of the juvenile skeleton of Paratrygon aiereba in comparison with juveniles of Potamotrygon tigrina, Potamotrygon schroederi and Potamotrygon leopoldi. For this, detailed morphological character traits and meristic data of the cranium, postcranial skeleton, teeth and placoid scales are assembled. Our results also were compared with published accounts of Heliotrygon and Plesiotrygon. The most conspicuous characters of juvenile Paratrygon aiereba are: the (1) small anterior protuberance between nasal capsules, (2) large foramen posterior to the optic nerve foramen, (3) unique dermal denticle morphology and (4) characteristic tooth morphology. Our results derived from juveniles support previous interpretations that Paratrygon and Heliotrygon share several anatomical features including a considerable wide internasal septum and a high number of pectoral radials indicating closer relationships. Juvenile Paratrygon can be readily distinguished from juvenile Potamotrygon by: (1) a nearly complete connection of the anterior radials of the pectoral fins by a distinct ligament (“functional rostrum”), (2) the small protuberance between the nasal capsules (rudimental rostrum), (3) a considerable wider occipital region in the studied growth stages, (4) a wider first synarcuale and subsequently (5) a considerable wider pectoral girdle. Morphological variations between both juvenile Paratrygon and Potamotrygon include a taxonomic signal (shorter and wider cranium (smaller length of fontanelle and neurocranium, wider distance between postorbital processes), wider synarcuale (wider distance between lateral stays), a longer “functional rostrum” (greater prenasal and preoral length) and a shorter medial prepelvic process in Paratrygon) according to the principle-component-analyses (PCA) using the variance–covariance matrix conducted here. Nevertheless, more specimens of P. aiereba and Potamotrygon spp. and additional specimens of Heliotrygon and Plesiotrygon representing different growth stages are necessary to establish detailed growth trajectories in freshwater stingrays for identifying phylogenetic signals.

Phylogeography and conservation genetics of the Amazonian freshwater stingray Paratrygon aiereba Müller &amp; Henle, 1841 (Chondrichthyes: Potamotrygonidae)

The family Potamotrygonidae is monophyletic comprising three genera: Paratrygon Duméril, Potamotrygon Garman and Plesiotrygon Rosa, Castello &amp; Thorson. The distribution of most species in this family is restricted to a single basin or fluvial system. Only Potamotrygon motoro, Potamotrygon orbignyi and Paratrygon aiereba are found in more than one river basin. In this study we investigate genetic structuring of Paratrygon aiereba, from five rivers of the Amazon region: Negro, Solimões-Amazon-Estuary system, Tapajós, Xingu and Araguaia. Sixty-three individuals were sequenced for ATPase 6, and a representative subsample of 27 individuals was sequenced for COI. The COI dataset analysis indicated that Paratrygon is sister to all other potamotrygonid genera and species. Population parameters inferred from the analysis of ATPase 6 sequences revealed that the populations of this species are structured within each river, with no or nearly non-existent gene flow occurring between rivers and a positive correlation between geographic and genetic distances. Paratrygon aiereba is comprised of three geographically restricted clades with K2P interclade distances of at least 2%. Intraspecific divergence within P. aiereba is similar to the interspecific divergence observed in Potamotrygon spp. sampled throughout the same geographic area. Using the premises of COI barcoding and the allopatric distribution of the three P. aiereba clades, the taxon P. aiereba most likely comprises three distinct biological species. Since freshwater stingrays of the family Potamotrygonidae are highly exploited for the aquarium trade, management and conservation strategies need to be implemented at the level of each river basin, rather than at the level of the Amazon basin.

Mitochondrion-rich cells distribution, Na+/K+-ATPase activity and gill morphometry of the Amazonian freshwater stingrays (Chondrichthyes: Potamotrygonidae)

Detailed measurements of gill area and constituent variables (total filament number, total filament length and mean filament length), and immunolocalization of the α-subunit of Na⁺/K⁺-ATPase and Na⁺/K⁺-ATPase activity were performed on both hemibranchs of all five arches of freshwater potamotrygonid stingrays (Paratrygon aiereba and Potamotrygon sp.). Both species exhibit similar mass-specific gill area, 89.8 ± 6.6 and 91.5 ± 4.3 mm² g⁻¹ for P. aiereba and Potamotrygon sp., respectively. The density of Na⁺/K⁺-ATPase-rich MRCs and Na⁺/K⁺-ATPase activity was higher in the 4th gill arch in both species. The Na⁺/K⁺-ATPase activity was positively correlated to the Na⁺/K⁺-ATPase-rich Na⁺/K⁺-ATPase rich) mitochondrion-rich cell (MRC) distribution among the gill arches of P. aiereba but not in Potamotrygon sp. The levels Na⁺/K⁺-ATPase activity were not correlated to the gill surface area among the arches for both rays' species. Considering that the Na⁺/K⁺-ATPase-rich MRC is the main site for active ion transport in the gill epithelia and Na⁺/K⁺-ATPase activity plays a crucial role in osmoionoregulatory function, we suggesting that 4th gill arch is more relevant for osmoregulation and ion balance in these potamotrygonids.

Morphology of lateral line canals in Neotropical freshwater stingrays (Chondrichthyes: Potamotrygonidae) from Negro River, Brazilian Amazon

The relationship between the distribution of the lateral line canals and their functionality has not been well examined in elasmobranchs, especially among Neotropical freshwater stingrays of the family Potamotrygonidae. The spatial distribution of the canals and their tubules and the quantification of the neuromasts were analyzed in preserved specimens of Potamotrygon motoro, P. orbignyi, Potamotrygon sp. "cururu", and Paratrygon aiereba from the middle Negro River, Amazonas, Brazil. The hyomandibular, infraorbital, posterior lateral line, mandibular, nasal and supraorbital canals were characterized and their pores and neuromasts quantified. The ventral canals are known to facilitate the accurate localization of prey items under the body, and our results indicate that the dorsal canals may be employed in identifying the presence of predators or potential prey positioned above the stingray's body. The presence of non-pored canals in the ventral region may be compensated by the high concentration of neuromasts found in the same area, which possibly allow the accurate detection of mechanical stimuli. The concentration of non-pored canals near the mouth indicates their importance in locating and capturing prey buried in the bottom substrate, possibly aided by the presence of vesicles of Savi.

Ionic regulation and Na+–K+‐ATPase activity in gills and kidney of the freshwater stingray Paratrygon aiereba living in white and blackwaters in the Amazon Basin

During low-water period, freshwater stingray Paratrygon aiereba collected in the whitewater (WW) of the River Amazon showed higher urea content, osmolality, Na(+) and Cl(-) concentrations in plasma and perivisceral fluid than those caught in blackwater (BW) of the River Negro. Gills and kidney Na(+)-K(+)-ATPase activities were significantly lower in WW than in BW fish. The high level of kidney Na(+)-K(+)-ATPase activity in P. aiereba may minimize ion loss and generate diluted solute-free urine in ion-poor BW environment.

DIVERSIDADE DE RAIAS DE ÁGUA DOCE (Chondrichthyes : Potamotrygonidae) NO ESTUÁRIO AMAZÔNICO

Um levantamento sobre registros de ocorrência de raias de água doce (Potamotrygonidae) no estuário amazônico foi realizado utilizando-se dados bibliográficos, informações de coleções científicas disponíveis on-line e amostragens de campo. Os resultados indicaram a presença de oito espécies nominais: Plesiotrygon iwamae, Paratrygon aiereba,Potamotrygon humerosa, Potamotrygon motoro, Potamotrygon cf. ocellata, Potamotrygon orbignyi,Potamotrygon scobina e Potamotrygon aff. hystrix. Apenas cinco destas espécies são atualmente consideradas cientificamente válidas. Adicionalmente a estas, foram identificadas ao menos mais duas espécies e um gênero novo queno momento estão em processo de descrição. O número de espécies ocorrentes no estuário amazônico ainda é incerto, podendo variar de cinco a dez dependendo dos avanços e revisões sistemáticos que venham a ser realizados neste grupo de elasmobrânquios.