Nematode parasites of fishes from Santa Luzia River, state of Acre, Western AmazonAbstract
The Amazon Basin is undeniably a biodiversity hotspot, featuring the highest freshwater biodiversity on Earth, however, this area is facing increasing anthropogenic threats. Although this basin hosts the highest diversity of freshwater fishes in the world, few fish species have been recorded in the State of Acre. Nematoda represents one of the most important and frequent group of helminth parasites of freshwater, marine, or brackish-water organisms, and yet knowledge of this group remains incomplete. During studies on the helminth fauna of fishes in the Santa Luzia River, State of Acre, different fish species were examined. Cichlasoma amazonarum represents a new host record for Touzeta ecuadoris and Procamallanus (Spirocamallanus) sp.; Ctenobrycon spilurus represents a new host record for Procamallanus (Spirocamallanus) sp.; and Cheirocerus eques is a new host for Procamallanus (Procamallanus) sp. and Rhabdochona sp. In addition, Procamallanus (Spirocamallanus) inopinatus was recorded in Leporinus friderici. Future collections from these hosts will make it possible to obtain male specimens of some of these Nematoda, allowing precise identification of some of these species. Despite the importance of helminths, there are many species that still need to be discovered and described before the inventory of the biodiversity of existing parasites can be considered complete.
Keywords:
Nematoda; parasites of fishes; ichtyoparasitology; Western Amazon
Resumo
A Bacia Amazônica é inegavelmente um hotspot de biodiversidade, apresentando a maior biodiversidade de água doce da Terra e enfrenta um aumento nas ameaças antropogênicas. Apesar desta bacia abrigar a maior diversidade de peixes de água doce do mundo, poucas espécies de peixes foram registradas no estado do Acre. Nematoda representa um dos grupos mais importantes e frequentes de helmintos parasitas de organismos de água doce, marinha ou salobra, mas o conhecimento sobre esse grupo ainda permanece incompleto. Durante estudos sobre a fauna de helmintos de peixes no Rio Santa Luzia, estado do Acre, foram examinadas diferentes espécies de peixes. Cichlasoma amazonarum representa um novo registro de hospedeiro para Touzeta ecuadoris e Procamallanus (Spirocamallanus) sp.; Ctenobrycon spilurus representa um novo registro de hospedeiro para Procamallanus (Spirocamallanus) sp.; e Cheirocerus eques é um novo hospedeiro para Procamallanus (Procamallanus) sp. e Rhabdochona sp. Além disso, Procamallanus (Spirocamallanus) inopinatus foi registrado em Leporinus friderici. Futuras coletas desses hospedeiros permitirão a obtenção de espécimes machos de alguns destes Nematoda, permitindo a identificação precisa de algumas destas espécies. Apesar da importância dos helmintos, há muitas espécies que ainda precisam ser descobertas e descritas antes que o inventário da biodiversidade dos parasitos existentes possa ser considerado completo.
Palavras-chave:
Nematoda; parasitos de peixes; ictioparasitologia; Amazônia Ocidental
1. Introduction
The hydrographic network of the Neotropical Region hosts the most diverse freshwater fish fauna in the world, with approximately 5,160 species (Reis et al., 2016; Jézéquel et al., 2020). Although the Amazon River basin is the largest and most diverse freshwater system on the planet, to date, only about 2,406 fish species have been recorded in this basin, including around 1,402 endemic forms (Dagosta and De Pinna, 2019; Jézéquel et al., 2020). The Amazon Basin is undeniably a biodiversity hotspot, featuring the highest freshwater biodiversity on Earth, however, this area is facing increasing anthropogenic threats. In addition, despite this basin hosting the highest diversity of freshwater fish in the world (Levêque et al., 2008; Winemiller et al., 2016), few fish species have been recorded in the State of Acre. It is believed that the ichthyofauna of this area is poorly understood due to its geographical isolation and distance from the main centers of ichthyological research in the country (Anjos et al., 2008).
Taxonomy and systematics constitute the basis for all research in ecology and evolution, as well as in applied fields like fisheries and aquaculture. To advance our understanding of parasites, they must first be identified and characterized, to enable differentiation from other species (Poulin et al., 2020). Considering the scarce information available concerning the ecological aspects of the parasitism of fishes from Acre, the aim of the current study was to characterize the fish nematode fauna of the Santa Luzia River, contributing to the knowledge of Acre's biodiversity.
Although Nematoda represents one of the most important and frequent group of helminth parasites of freshwater, marine, or brackish-water organisms, knowledge of this group remains incomplete, and many issues related to biology, ecology, taxonomy, phylogeny, and biogeography need to be clarified. Despite their great taxonomic diversity, some species are difficult to identify, and many not yet have been collected or described (Moravec, 2007; Hodda, 2007,2022).
During studies on the helminth fauna of fishes in the Santa Luzia River, in Acre, one of the most biodiverse states in the Brazilian Amazon, specimens of different fish species were examined, and the nematodes found are described herein.
2. Material and Methods
In August 2024, a survey was carried out of the helminth fauna in fishes in the Santa Luzia River, State of Acre, municipalities of Cruzeiro do Sul, Brazil (07º 37’ 52” S and 72º 40’ 12” W). This river is located in the Settlement Project and Development (SPD) Santa Luzia (Figure 1). Collections in this study were authorized by the Brazilian Government’s Chico Mendes Institute for Biodiversity and Conservation (ICMBIO, license number 39687-1).
Map of Settlement Project and Development (SPD) Santa Luzia, where the Santa Luzia River is located.
Thirty-two specimens of fishes belonging to 9 species were studied, as follows: 2 Cichlasoma amazonarum Kullander, 1983, 1 Crenicichla reticulata (Heckel, 1840), 3 Crenicichla sp. (Cichliformes); 1 Bryconops caudomaculatus (Günther, 1864), 9 Ctenobrycon spilurus (Valenciennes, 1850), 1 Hoplerythrinus unitaeniatus (Spix & Agassiz, 1829), 3 Leporinus friderici (Bloch, 1794), 3 Bario oligolepis (Günther, 1864) (Characiformes); and 9 Cheirocerus eques Eigenmann, 1917 (Siluriformes).
The fishes were acquired with the aid of local fishermen and examined for parasites immediately after capture. Internal organs were separated in Petri dishes containing 0.65% NaCl and examined with the aid of a stereoscopic microscope. The nematodes found were washed in 0.65% NaCl and fixed in hot ethanol 70%. For light microscopical examination (LM), the nematodes were cleared in Amann’s lactophenol and observed and photographed using a Zeiss Axioscope 2 microscope with differential interference contrast (DIC). All measurements are given in millimeters; range values are followed by means.
3. Results
From the 9 species of fishes examined, C. reticulata, Crenicichla sp., B. caudomaculatus, H. unitaeniatus, and B. oligolepis were negative for endohelminths. The nematodes found in the other fishes are detailed in Table 1 and morphometric data are presented herein.
Different host species with standard body length and weight in parenthesis, parasites, number of parasitized hosts/ numbers of examined hosts (NP/NE), total number of parasites (TNP), site of infection (SI) [intestine (Int), gall bladder (GB)].
Family Quimperiidae Gendre, 1928
Genus Touzeta Petter, 1987
Touzeta ecuadoris Petter, 1987 (Figures 2 and 3)
Touzeta ecuadoris Petter, 1987, female. A. Anterior region with oesophagus divided into an anterior region (ar) and posterior region (pr); B. Eggs in uterus (e); C. Posterior end. Bars 0.2 mm.
Touzeta ecuadoris Petter, 1987, male. A. Anterior region with oesophagus divided into an anterior region (ar) and posterior region (pr), and excretory pore situated at the level of posterior region of oesophagus (arrowhead). Bar 0.2 mm. B. Anterior extremity showing a small buccal cavity without sclerotized walls and small pseudobuccal capsule. Bar 0.05 mm. C. Posterior region showing a pseudosucker (arrow) on precloacal region. Bar 0.2 mm. D. Posterior region showing one of the spicules (S). Some postcloacal papillae are also visible (thin arrows). Bar 0.1 mm.
Host: Cichlasoma amazonarum Kullander, 1983 (Cichlidae, Cichliformes)
Description:
Female (based on 2 specimens): Body whitish, slender, 5.30–6.30 long and 0.49–0.52 wide. Cephalic end rounded, without lips. Oral aperture large, surrounded by distinct cephalic papillae. Small buccal cavity without sclerotized walls and small oesophastome present. Oesophagus divided into an anterior region, 0.122–0.235 long, and a posterior region, 0.345–0.350 long (Figure 2A). Nerve ring situated at anterior region of oesophagus, before the junction of both parts of oesophagus, at 0.185–0.195 from anterior region of body. Excretory pore at the level of posterior region of oesophagus, 0.520–0.675 from anterior extremity. Vulva at 3.23 from anterior region of body. Uterus with rounded eggs, 0.075–0.082 long and 0.057–0.067 wide (Figure 2B). Tail slender with a pointed tip, 0.405 long (Figure 2C).
Male (based on 2 specimens): Length of body 3.92–4.05 long, maximum width 0.310–0.350. Small buccal cavity without sclerotized walls and small oesophastome present (Figure 3B). Anterior region and posterior region of oesophagus 0.195–0.215 and 0.280–0.320, respectively (Figure 3A). Nerve ring and excretory pore at 0.150–0.155 and 0.430–0.540 from anterior extremity, respectively (Figure 3A). Precloacal region bearing a pseudosucker at 0.715–0.850 from posterior extremity (Figure 3C). Eight pairs of precloacal papillae, 1 pair of adanal papillae and 4 pairs of postanal papillae. Spicules equal, 0.130–0.160 long. Gubernaculum present, triangular, 0.04–0.05 long. Tail conical, 0.270 long (Figure 3D).
Remarks:
Touzeta Petter, 1987 is a monotypic genus, with a single species, Touzeta ecuadoris Petter, 1987, which was described from an unidentified cichlid from the Amazon River Basin of Ecuador (Petter, 1987). Souza-Neto et al. (2023) reported T. ecuadoris from Bujurquina cordemadi Kullander, 1986 (Cichliformes) from Moa River, State of Acre (Western Amazonas), but no morphometric parameters of this species were given. Moravec and Prouza (2024) described two immature females from Cichlidae gen. sp. (Cichliformes) from the eastern part of the Andes Mountains, Amazon River basin of Ecuador. The present study comprises the first description and morphometric characterization of this species from Brazil and C. amazonarum constitutes a new host record for this species.
Family Camallanidae Railliet & Henry, 1915
Genus Procamallanus Baylis, 1923
Subgenus Procamallanus (Spirocamallanus) Olsen, 1952
Procamallanus (Spirocamallanus) sp. (Figure 4)
Procamallanus (Spirocamallanus) sp. (female), parasite of Ctenobrycon spilurus (Valenciennes, 1850). A. Anterior region showing buccal capsule with spiral thickenings and an oesophagus divided into a muscular region (mr) and a glandular region (gr). Bar 0.35; B. Middle of body with many larvae in the uterus. Bar 0.20 mm; C. Posterior region showing the anus (arrowhead). Bar 0.30 mm.
Hosts: Cichlasoma amazonarum Kullander, 1983 (Cichlidae, Cichliformes) and Ctenobrycon spilurus (Valenciennes, 1850) (Characidae, Characiformes)
Description (Based on 1 female from C. amazonarum and 2 females from C. spilurus; measurements of C. spilurus are in brackets): Body 11 [15.35–21.7] long and 0.72 [0.67–0.75] in maximum wide. Orange-brown buccal capsule 0.11 [0.085–0.125] long and 0.125 [0.125–0.130] wide, with 17 [17–18] spiral thickenings in number. Muscular and glandular oesophagus 0.355 [0.355–0.420] and 0.98 [1.02–1.04] long, respectively (Figure 4A). Nerve ring and excretory pore at 0.242 [0.205–0.240] and 0.310 [0.275] from anterior region, respectively. Vulva at [9.18] from posterior region. Middle of body with many larvae in the uterus (Figure 4B). Tail conical, 0.26 [0.26–0.33] long (Figure 4C).
Remarks:
The nematode genus Procamallanus Baylis, 1923 includes many species distributed worldwide that primarily parasitize freshwater and marine fish. The subgenus Procamallanus (Spirocamallanus) Olsen, 1952 comprises a huge number of species that are widespread in the Neotropical Region. In the present study, only females were found, leading to the impossibility of identifying this Nematoda in the specific level due to the absence of male specimens.
Procamallanus (Spirocamallanus) inopinatus Travassos, Artigas & Pereira, 1928 (Figure 5)
Procamalanus (Spirocamallanus) inopinatus Travassos, Artigas & Pereira, 1928 parasite of Leporinus friderici (Bloch, 1794). A. Anterior region showing a buccal capsule with spiral ridges and an oesophagus divided into a muscular region (mr) and a glandular region (gr). Bar 0.3 mm; B. Middle portion of the female's body showing the vulva, post-equatorial (arrowhead). Bar 0.3 mm; C. Posterior region of female showing anus (arrow) Bar 0.3 mm; D. Posterior region of the male showing one of the spicules (arrow). Bar 0.2 mm.
Host: Leporinus friderici (Bloch, 1794) (Anostomidae, Characiformes)
Description:
Female (based on 3 specimens). Body 12.72–17.55 long and 0.47–0.62 wide. Buccal capsule orange-brown, measuring 0.130–0.142 long and 0.123–0.125 wide, with inner surface provided with 12–17 spiral ridges. Muscular region of oesophagus 0.47–0.49 in length and glandular region 0.78–0.79 in length (Figure 5A). Distance of nerve ring and excretory pore 0.25–0.30 and 0.44 from anterior extremity, respectively. Vulva postequatorial, 5.69 from posterior extremity (Figure 5B). Tail conical, with anus situated at 0.185–0.230 from posterior region (Figure 5C)
Male (based on 1 specimen). Body ventrally curved, 4.67 in length and 0.28 in width. Orange-brown buccal capsule, with 12 spiral ridges, 0.09 long and 0.07 wide. Muscular and glandular region of oesophagus 0.34 and 0.58 long, respectively. Nerve ring at 0.187 from anterior extremity. Two spicules 0.12 long, and 10 pairs of papillae (4 pairs of precloacal papillae and 6 pairs of postcloacal papillae), at posterior region of body (Figure 5D).
Remarks:
Procamallanus (S.) inopinatus presents a wide geographical distribution and low host specificity. This species has been reported in different host genera, while in the genus Leporinus Spix, 1829, it has been reported in several species, including Leporinus agassizii Steindachner, 1876, Leporinus fasciatus (Bloch, 1794), Leporinus lacustris Amaral Campos, 1945, Leporinus octofasciatus Steindachner, 1915, Leporinus piau Fowler, 1941, Leporinus striatus Kner, 1858, Leporinus taeniatus Lütker, 1875, Leporinus sp., Leporinus friderici (Bloch, 1794), besides in hosts previously assigned in Leporinus, as Hypomasticus copelandii(Steindachner, 1875) (as Leporinus copelandii), Megaleporinus elongatus(Valenciennes, 1850) (as Leporinus elongatus), Megaleporinus obtusidens (Valenciennes, 1837) (as Leporinus obtusidens), and Megaleporinus reinhardti(Lütken, 1875) (as Leporinus reinhardti) (Luque et al., 2011; Martins et al., 2017a,b; Amaral et al., 2023). This nematode species had already been recorded from Acre parasitizing L. jamesi and L. moralesi (Virgílio et al., 2022; Souza-Neto et al., 2023).
Subgenus Procamallanus (Procamallanus) Baylis, 1923
Procamallanus (Procamallanus) sp. (Figure 6)
Procamallanus (Procamallanus) sp. (female), parasite of Cheirocerus eques Eigenmann, 1917. A. Anterior region showing an orange-brown buccal capsule with a smooth inner surface, and the muscular region of oesophagus (mr); B. Middle region of body with the uterus bearing many larvae. Bar 0.30 mm; C. posterior region showing the anus (arrow). Bar 0.10 mm.
Host: Cheirocerus eques Eigenmann, 1917 (Pimelodidae, Siluriformes)
Female (based on 2 specimens): Body 14.0–14.3 long and 0.29–0.30 wide. Orange brown buccal capsule, inner surface smooth, 0.080–0.085 long (including basal ring) and 0.055–0.057 wide (Figure 6A). Muscular region of oesophagus 0.475–0.510 long and glandular region 0.59–0.65 long. Nerve ring and excretory pore at 0.245–0.250 and 0.400 from anterior region, respectively. Vulva at 7.45 from the posterior end of body. Uterus with numerous larvae, 0.275–0.300 long (Figure 6B). Tail conical, at 0.205–0.217 long (Figure 6C).
Remarks:
Procamallanus (Procamallanus) Baylis, 1923 is characterized by presenting a buccal capsule with no ridges on its inner surface. Among this subgenus only three species have been reported from Brazil: P. (P.) peraccuratus Pinto, Fabio, Noronha & Rolas, 1976, P. (P.) annipetterae Kohn & Fernandes, 1988, and P. (P.) spiculastriatus Pinheiro, Melo, Monks, Santos & Giese, 2018 (Pinto et al., 1976; Petter and Dlouhy, 1985; Kohn and Fernandes, 1988; Pinheiro et al., 2018). In the present study only two females were found, making it impossible to identify accurately at species level.
Family Rhabdochonidae Skrjabin, 1946
Rhabdochona sp. (Figure 7)
Rhabdochona sp. parasite of Cheirocerus eques Eigenmann, 1917. A. Anterior region of female. Bar 0.10 mm; B. Middle body of female showing the vulva (V). Bar 0.10 mm; C. Posterior region of female showing anus (arrow). Bar 0.10 mm; D. Anterior region of male undergoing molt, with old cuticle shedding (asterisk). Bar 0.12 mm; E. Posterior region of the male showing the smaller spicule (arrowhead). Bar 0.11mm.
Host: Cheirocerus eques Eigenmann, 1917 (Pimelodidae, Siluriformes)
Female (based on 2 specimen). Body 8.02–8.05 long, 0.13–0.17 maximum wide. Prostom 0.025 long and 0.0175–0.020 wide. Vestibule including prostom 0.150–0.162 long (Figure 7A). Muscular and glandular portions of oesophagus with 0.27–0.34 and 1.06–1.25 long, respectively. Nerve ring to anterior region 0.20–0.77. Excretory pore not observed. Vulva at 3.52–4.33 from the posterior end of body (Figure 7B). Posterior region tapered (Figure 7C). One of the specimens was undergoing molt.
Male (based on 1 specimen). Body 6.40 long by 0.12 maximum wide. Prostom 0.02 long and 0.01 wide. Vestibule including prostom 0.127 long (Figure 7D). Muscular and glandular portions of oesophagus 0.24 and 1.04 long, respectively. Nerve ring 0.157 to anterior region. Excretory pore not observed. Spicules unequal, right spicule 0.11 long, left 0.57 long (Figure 7E). Papillae not counted.
Remarks:
To date, there are four known species of Rhabdochona Railliet, 1916 reported from South America: Rhabdochona acuminata (Molin, 1860), Rhabdochona fabianae Ramallo, 2005, Rhabdochona uruyeni (Díaz-Ungría, 1968), and Rhabdochona fuscovaria Alcantara, O´Dwyer & Silva, 2021. The first three have been recorded in freshwater fishes, while the latter was recently described from an anuran host (Moravec, 1972; Ramallo, 2005; Pinto et al., 2010; Alcântara et al., 2021). The specimens of the present study were suffering molt and were in bad morphological conditions, making it impossible to identify them to species. The present finding of Rhabdochona sp. represents the first record of this genus in C. eques.
4. Discussion
Parasites play an important role in ecosystems, as they can regulate the abundance of host fish populations, destabilize food webs, and change the structure of host communities. Despite their importance, they are one of the least studied groups in most biodiversity studies (Marcogliese and Cone, 1997; Lafferty, 2008; Adlard et al., 2015; Acosta et al., 2020).
The study of fish parasitic nematodes from natural environments in Acre remains underestimated. There are some records of these helminths in Pimelodus blochii Valenciennes, 1840 (Negreiros et al., 2018; 2019a, b; Cavalcante et al., 2020) and Calophysus macropterus (Lichtenstein, 1819) (Negreiros et al., 2019c), and, more recently, studies of the endohelminths of different fishes from the Upper Juruá River have been recorded (Virgílio et al., 2022, 2023; Souza-Neto et al., 2023). In addition, there have also been some records of Nematoda from fish farms in Acre in the hosts Arapaima gigas (Schinz, 1822) (Silva et al., 2016, 2017) and Megaleporinus macrocephalus (Garavello & Britski, 1988) (as Leporinus macrocephalus) (Martins et al., 2017a, b; Negreiros et al., 2021).
New species of endohelminths parasitizing P. blochii have been described from rivers from the state of Acre, such as the nematodes Orientatractis moraveci Cavalcante, Silva, Santos, Chagas-Moutinho & Santos, 2016 and Philometroides acreanensis Cavalcante, Moravec & Santos, 2017, demonstrating the high species richness of the region (Cavalcante et al., 2017, 2018). More recently, the male of P. acreanensis was described from the same host and locality (Negreiros et al., 2019a). The nematode Cystidicoloides vaucheri Petter, 1984 was redescribed from Phractocephalus hemioliopterus (Bloch & Schneider) from Acre River, State of Acre (Pereira et al., 2018).
Among the nematodes found in the present study, T. ecuadoris and Procamallanus (S.) sp. are being reported in C. amazonarum for the first time. Until now, this nematode has been only reported from Ecuador (Petter, 1987; Moravec and Prouza, 2024), and from the Moa River, western Amazon (state of Acre) (Souza-Neto et al., 2023). Thus, only a few years ago, this species was considered very restricted in its geographical range and hosts, since there was only the record of Petter (see Pérez-Ponce de Leon and Choudhury, 2005). In fact, T. ecuadoris does not appear to be a generalist species, and to date has only been reported in cichlids. However, further studies in the western Amazon, including the Peruvian Amazon, could expand the records of this species, allowing better understanding of its geographical distribution as well as its biology.
The subgenus Procamallanus (Spirocamallanus) presents a wide geographical distribution and has been reported in several hosts. The species from this genus reported in the State of Acre, in different host fishes, include Procamallanus (Spirocamallanus) rarus Travassos, Artigas & Pereira, 1928, P. (Spirocamallanus) pimelodus Pinto, Fábio, Noronha & Rolas, 1974 from P. blochii, P. (S.) inopinatus, Procamallanus (S.) sp., Procamallanus (Spirocamallanus) pintoi (Kohn and Fernandes, 1988), Procamallanus (S.) solani Pinto, Fabio, Noronha & Rolas, 1975, and Procamallanus (S.) sp. (Martins et al., 2017a, b; Negreiros et al., 2018, 2019b; Cavalcante et al., 2020; Virgílio et al., 2022, 2023; Souza-Neto et al., 2023). Ctenobrycon spiluris and C. amazonarum represent new host records for Procamallanus (S.) sp. Future collections from these hosts may enable the obtention of male specimens of this Nematoda for accurate identification.
In the present study, P. (S.) inopinatus was found in L. friderici. This species has been reported in the same host, collected from a dam in the State of Minas Gerais (Feltran et al., 2004), in the Upper Paraná River, State of Paraná (Guidelli et al., 2006, Takemoto et al., 2009), in tributaries of the Amazon River, such as the Jari River and Igarapé Fortaleza River, State of Amapá (Oliveira et al., 2017, 2019), and the Traíras River, State of Goiás (Amaral et al., 2023). These findings corroborate those of Neves et al. (2020), who demonstrated that P. (S.) inopinatus has a low specificity to hosts and high adaptability to different freshwater habitats in Brazil, with a wide geographic distribution.
Cheirocerus eques represents a new host record for Procamallanus (P.) sp. and Rhabdochona sp. These results contribute to knowledge of the biodiversity of this locality, and further studies are important for the identification of these nematodes at a specific level. The only species from the subgenus Procamallanus (P.) reported in Acre is Procamallanus (Procamallanus) peraccuratus (Virgílio et al., 2022, 2023; Souza-Neto et al., 2023), which parasitizes mainly cichlid fishes, but can occasionally be found in other groups of fishes, such as Siluriformes.
Species of Rhabdochona, which are exclusively freshwater parasites, are distributed in all zoogeographical regions (Moravec, 2010). Although species from the genus Rhabdochona have not been reported in fishes from natural environments from Acre, R. acuminata was found in Megaleporinus macrocephalus (as Leporinus macrocephalus) from fish farms in the State of Acre (Martins et al., 2017a, b; Negreiros et al., 2021). Therefore, C. eques is a new host record for species of this genus. Further studies could clarify the specific identification of Rhabdochona sp., and new hosts for this species may be found in the region.
Reis et al. (2021), in a checklist of nematodes from the Brazilian Amazon, demonstrated that, although there was an increase in taxonomic studies in the region between 2010 and 2020, when related to the size of the area studied and considering that it is recognized as megadiverse, the number of articles produced is still low, indicating a significant knowledge deficit in this region. Therefore, efforts are still required to study this biodiversity hotspot.
Thus, there is a gap in the knowledge of these helminths in fishes from this region, which contains a huge river basin and great ichthyological diversity. Despite the importance of parasites, it is known that many species still need to be discovered and described before the inventory of the biodiversity of existing parasites can be considered complete (Jorge and Poulin, 2018; Carlson et al., 2020; Poulin et al., 2023).
Acknowledgements
MQC is grateful for Research Support Foundation of the State of Rio de Janeiro (Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, FAPERJ - Project E-26/210.131/2025) support.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author.
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