Occurrence of Hyphessobrycon langeanii Lima & Moreira, 2003 (Characiformes, Characidae) in the upper Paraguay river basin

. Hyphessobrycon langeanii was originally described as endemic to the upper Araguaia river basin, Brazil. However, our analysis of several Hyphessobrycon specimens collected in the Correntes river basin and another tributary of the Itiquira River in Mato Grosso state (both belonging to the Paraguay river basin) reveals the first verified record of H. langeanii from this basin and from the states of Mato Grosso do Sul and Mato Grosso. The objective of this study is to provide a novel record of H . langeanii from the basin of the Paraguay River and from the state of Mato Grosso do Sul. We compare the newly discovered populations with the populations in the Ara-guaia river basin, and we also provide a brief discussion on the biogeography of this species.


Introduction
Hyphessobrycon Durbin, 1908 is a Neotropical genus of small-sized characids currently comprising more than 160 valid species (Fricke et al. 2023), which makes it one of the most diverse genera within the family Characidae and the order Characiformes. This genus is widespread throughout the Neotropical region, occurring from southern Mexico to northern Argentina, with the Amazon basin harboring about half of its species diversity (Ohara and Lima 2015).
Despite the large number of recently described species within the genus (e.g., García-Alzate et al. 2020;Faria et al. 2021;Dagosta et al. 2022), there are several still undescribed taxa. While the non-monophyletic status of the genus has been indicated in several studies of Characidae (e.g., Mirande 2019; Melo et al. 2022), the artificial diagnosis proposed by Eigenmann (1917) is still used when describing new species. Some authors have proposed putative monophyletic species-groups within Hyphessobrycon, using both color pattern and anal-fin hook morphology (e.g., Weitzman and Palmer 1997;Ingenito et al. 2013;Ota et al. 2020), but such species-groups still need to be tested in a more encompassing phylogenetic analysis.
Hyphessobrycon langeanii Lima & Moreira, 2003 was described from streams tributaries of the upper Araguaia river basin, with "córrego Mosquito" as the type locality, which is near the border of the states of Mato Grosso and Goiás. This species has been being treated as endemic to this region ever since. However, the recent mention of Hyphessobrycon cf. langeanii from the upper Paraguay river basin (Carvalho et al. 2022) led us to review material collected in tributaries of this basin around the headwaters of the upper Araguaia River. Our analysis of recently collected specimens from the headwaters of the Correntes river basin, plus material collected in the 1970s from the Itiquira river basin, has allowed us to confirm with taxonomic certainty the occurrence of H. langeanii in the upper Paraguay river basin in both Mato Grosso and Mato Grosso do Sul states.

Methods
The studied specimens of Hyphessobrycon langeanii (Fig. 1 Morphometric data were taken with digital calipers with 0.1 mm precision, and all measurements are in millimeters. Measurements and counts followed Fink and Weitzman (1974), with the exception of the scale rows below the lateral line, which were counted to the insertion of the pelvic fin. Horizontal scale rows between the dorsal-fin origin and the lateral line do not include the scale of the median predorsal series situated just anterior to the first dorsal-fin ray.  Chamon et al. (2022), there are 751 fish species in the Tocantins-Araguaia basin, and 22% of them are endemic, most belonging to the family Characidae, followed by Rivulidae and Loricariidae, and almost one-quarter of these (51 species) have been
(2022) also pointed out the presence of 69 endemic species in the Araguaia river basin, but this number will certainly increase, as new species are described, such as Paracanthopoma cangussu Henschel, Katz & Costa, 2021, which is exclusive to the middle Araguaia river drainage.
Comparing the most recent species lists for the Paraguay river basin (Froehlich et al. 2017; Gimênes Jr and Rech 2022) and Araguaia river basin (Jarduli et al. 2014;Chamon et al. 2022), we note that several species occur in both basins, with some of them also in other watersheds, such as the Paraná and Amazon river basins. However, some shared species present a narrowly endemic distribution, exclusively occurring in the region drained by both upper portions of the Araguaia, Correntes, and Taquari river basins. Aspidoras aldebaran Tencatt, Britto, Isbrücker & Pavanelli, 2022 is an example of a species with this distribution pattern. Similar to A. aldebaran, our new record of H. langeanii from the Correntes river basin reinforces the high endemicity of this region as a whole.
Carvalho et al. (2022) identified populations of Hyphessobrycon from the upper Correntes river basin as Hyphessobrycon cf. langeanii; at that time, they were not sure of the specific identity of the taxon and used "cf." Our study of this material and the comparison of the diagnostic characteristics presented in the original description has allowed us to confirm its identity as H. langeanii. In addition to the material examined from the Correntes river basin, we studied specimens of Hyphessobrycon sp. from the Itiquira river basin collected in 1977 (MZUSP 67273; Fig. 2b) almost 30 years before the original description, and we can confirm their identity as H. langeanii. In the Paraguay river basin, with the exception of the few specimens collected in the ribeirão Sozinho, H. langeanii seems to be restricted to the Correntes river basin stretch upstream of its sinkhole (17°36′41″S, 054°50′04″W). This distribution pattern is also found in Eigenmannia correntes Campos-da Paz & Queiroz, 2017, Melanorivulus dapazi Costa, 2005, Chara cidium chicoi da Graça, Ota &Domingues, 2019, andCyphocharax caboclo Melo, Tencatt &Oliveira, 2022; the upper Correntes River presents a relatively high degree of endemism within the upper Paraguay river basin. Ongoing studies in that region have revealed the presence of about 10 additional putatively undescribed and endemic species for the upper Correntes River (LFCT pers. obs.), which greatly increases the number of endemic species for this region.
Comparison of the morphometric data of the newly discovered population shows that the horizontal diameter of the eyes is larger from the Correntes River than specimens from the upper Araguaia river basin: 24.4-37.5 (mean 32.5) in the type specimens versus 40.3-48.5 (mean 44.1). This difference may represent intraspecific variation. Furthermore, the Correntes River specimens are relatively smaller than those originally described as H. langeanii from the Araguaia River. Another possible explanation is that the orbit diameter typically tends to be smaller in larger individuals when compared to juveniles due to negative allometry. Given that the only conspicuous difference found between the two populations is the orbit diameter, it seems unfounded to consider the Correntes river basin population as not conspecific with the Araguaia river basin population. The specimens examined from the Paraguay river basin present the same variations in color pattern as mentioned by Lima and Moreira (2003: 24), who noted small variations in the humeral spot in specimens preserved in alcohol: "Humeral spot well-defined, black, and round to horizontally oval. Thin vertical lines extend posterodorsally and anteroventrally from humeral spot". This variation was also observed in living individuals (Fig. 1b). Melo et al. (2022) proposed a headwater-capture event between the Correntes River and the Araguaia river basin to explain the close relationship between Cyphocharax caboclo (endemic to the upper Correntes river basin) and C. boiadeiro (endemic to the upper Araguaia river basin). This seems to be the case for H. langeanni, but with no speciation after the geographic isolation. Nevertheless, additional molecular studies can test if there are significant genetic differences. Beyond the sharing of species itself, the region drained by the headwaters of both Correntes and Taquari rivers, the upper Paraguay river basin, and the headwaters of the upper Araguaia river basin upstream the vicinity of the city of Barra do Garças, central Brazil, represent one of the smallest Amazonian bioregions; named "Upper Araguaia", it presents a high degree of endemism and species richness (Dagosta et al. 2020;Melo et al. 2022). This bioregion is located within the Cerrado, one of the world's biodiversity hotspots (Myers et al. 2000;Cardoso da Silva and Bates 2002). Contrasting its remarkable biodiversity, the Cerrado has suffered severe anthropogenic effects (Klink and Machado 2005), and there are alarming prospects for the integrity of its watersheds (Salmona et al. 2023). Considering this, there is an urgent need for additional research to better understand this bioregion's ichthyofauna by describing its diversity, assessing the conservation status of species, and proposing management programsto help mitigate of the expected future threats to the drainages of the Cerrado. cal support. We are grateful to Marcos Nunes, Heriberto Gimênes Jr., Ricardo Rech, and Matheus Alves for helping in the fieldwork. We also thank Flávio Lima and Fernando Dagosta for the unvaluable suggestions on the manuscript, Steven Grant for kindly reviewing the manuscript's English, Heriberto Gimênes Jr. and Hans Evers for sending and allowing the use of several photographs of living H. langeanii and collecting sites, and João Braz (UEMS/Coxim) for the general support to LFCT and VCG. The Internationale Gemeinschaft Barben Salmler Schmerlen Welse e.V. (Germany), the Ohio Cichlid Association (USA; 2020 Jim Smith Endowment Fund), and Steven Grant and Roland van Ouwerkerk provided financial support to LFCT for the collecting trips in the upper Correntes River. VCG is granted by CAPES ("Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior", process 88887.616464/2021-00) and FRC is granted by CNPq (process # 420620/2018-4) and FUNDECT ("Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul", process # 59/300.093/2017, SIAFEM 27248).  (2022) The emerald green tetra: a new restricted-range Hyphessobrycon (Characiformes: Characidae) from the upper rio