Diversity of potamodromous fishes in the Tocantins-Araguaia basin

Thiago Nascimento da Silva Campos¹ , Hasley Rodrigo Pereira², Phâmela Bernardes Perônico³, Carine Cavalcante Chamon⁴, Philip Teles Soares⁵ and Fernando Mayer Pelicice⁴

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Abstract​

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Introduction​

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Freshwater fishes developed an array of strategies to cope with environmental variation and explore resources to survive and recruit populations (Winemiller, 1989; Brown-Peterson et al., 2011). Potamodromous fishes, in particular, are iteroparous organisms that carry out migratory movements across the river network to complete their life cycle, using different habitats to maximize survival, growth and reproduction (Lucas, Baras, 2001; Brönmark et al., 2013). Movements vary among species, from small migrations (tens of kilometers) to long-distance movements (hundreds to thousands of kilometers), including different patterns, behaviors, environments, timing and direction (Barthem et al., 2017; Lucas, Baras, 2001; Carolsfeld et al., 2003; Makrakis et al., 2012; Dean et al., 2022; Herrera-R et al., 2024). Potamodromous fishes are found in all continents (excepting Antarctica), where they colonized river systems and associate environments.

Potamodromous fishes are deeply connected with human societies, as they generate a number of ecosystem services (Olden et al., 2020; Pelicice et al., 2023), especially those associated with fishing (Petrere et al., 2002; Duponchelle et al., 2021; Scarabotti et al., 2021). However, knowledge about basic aspects of their life cycle remains scarce or absent. In tropical ecosystems, where fish diversity is extraordinary (Winemiller et al., 2016), information on potamodromous fishes is commonly fragmented, incomplete or uncertain, sometimes lacking species lists, not to mention data on migratory routes, spawning sites and nursery areas; important biodiversity shortfalls persist, e.g., Linnean, Wallacean, Prestonian, Raunkieran. Furthermore, specific ecological needs and complex life cycles make these fishes highly vulnerable to environmental degradation. Main stressors include river regulation, habitat loss, changes in land use, the introduction of non-native species, overfishing, in addition to the adoption of inappropriate management practices (Pelicice et al., 2017; Bailly et al., 2021; Duponchelle et al., 2021; Santana et al., 2021; Lee et al., 2023). Currently, migratory fishes are threatened on a global scale, as their populations have consistently reduced worldwide over the last five decades (e.g., Brown et al., 2013; Agostinho et al., 2016; Deinet et al., 2020; Ohms et al., 2022; Huang, Li, 2024).

The diversity of potamodromous fishes is especially high in the Neotropics. The group is composed of hundreds of species with different sizes, behaviors, life cycles and geographic distribution (Carolsfeld et al., 2003; Herrera-R et al., 2024), including iconic species with giant body sizes and continental migratory patterns (Barthem et al., 2017). Despite the social and economic importance of these fishes, knowledge about the group remains very incomplete. Studies have been conducted in the La Plata and São Francisco basins (e.g., Agostinho et al., 2003; Sato, Godinho, 2003), and only recently more complete surveys and syntheses have focused on Amazon fishes (Barthem et al., 2017; Dagosta, de Pinna, 2019; Duponchelle et al., 2021; Herrera-R et al., 2024). Yet, some regions remain poorly investigated, such as the Tocantins-Araguaia basin, marked by high fish diversity, endemism and relative geographic isolation (Ribeiro et al., 1995; Dagosta, de Pinna, 2017; Chamon et al., 2022). Located in Brazil, this basin (ca. 770,000 km²) is formed by two large rivers that flow across savannahs and rainforests, i.e., the Tocantins River, marked by fish endemism, and the Araguaia River, which holds a large floodplain system (Bananal Island; Latrubesse et al., 2019). Recent studies compiled a species list for the basin (ca. 751 species; Dagosta, de Pinna, 2019; Chamon et al., 2022), but the migratory status of these fishes remains uncertain.

The lack of information about potamodromous fishes in the Tocantins-Araguaia basin raises concerns, because this basin has been subjected to large-scale environmental degradation (Latrubesse et al., 2019; Pelicice et al., 2021; Ferreira et al., 2022); currently, 53 fish species are listed as threatened with extinction, the highest number in the Amazon region (Santana et al., 2021). This scenario is particularly unfavorable to migratory fishes, stressing the need for more information about this group. In this context, the present study investigated taxonomic and functional diversity of potamodromous fishes in the Tocantins-Araguaia basin, with the aim to (i) compile a species list, (ii) examine species richness, composition and functional diversity, and (iii) investigate fish diversity patterns considering spatial, taxonomic, and migration aspects. This is the first broad assessment focused on migratory fishes in this basin, with potential to generate basic information to support fisheries management, environmental planning, and conservation initiatives.

Material and methods

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Study area. The Tocantins-Araguaia basin drains approximately 770,000 km² of central/northern Brazil (Fig. 1), with an average discharge of ca. 11,000 m³/s (Ribeiro et al., 1995). The Tocantins River (ca. 343,000 km²) is a main channel of the basin; originally, its upper and middle stretches were channelized and characterized by the presence of rapids and waterfalls, while the lower stretch was marked by lowlands and some floodplain development. This river runs in the south-north direction (ca. 2,500 km) towards the Marajó Island, near the confluence of the Amazon River with the Atlantic Ocean. The Araguaia River (ca. 382,000 km²) is another main channel of the basin. This river is free-flowing (ca. 2,100 km) and characterized by the presence of a large floodplain system, the Bananal Island (Latrubesse, Stevaux, 2002). Both rivers run across a landscape dominated by savannah vegetation, with Amazon rainforests in the lower stretch.

FIGURE 1| The Tocantins-Araguaia Basin. The map indicates drainage limits (Tocantins and Araguaia), the studied sections (dark blue = upper/middle Tocantins; soft blue = lower Tocantins; black = Araguaia Basin), land cover categories, and operational small (CGH and PCH) and large dams (UHE).

The Tocantins River is divided in three main sections: upper, middle and lower (Ribeiro et al., 1995). The upper Tocantins (ca. 1,060 km) extends from Central Brazil to the confluence with the Paranã River, characterized by steep slopes with elevations varying from 1,400 to 300 m a.s.l. The middle Tocantins (ca. 980 km) extends to the confluence with the Araguaia River, flowing through gentle slopes (300 to 100 m a.s.l.). The lower Tocantins is a lowland area (ca. 360 km) with gentle slopes (100 to 0 m a.s.l.), where the river flows towards the estuary of the Amazon River. Several tributary rivers flow into the Tocantins River, such as the Almas, Paranã, Manoel Alves, Sono and Itacaunas.

The Araguaia River is also divided in three main sections: upper, middle and lower (Ribeiro et al., 1995; Latrubesse, Stevaux, 2002). The upper Araguaia River (ca. 450 km) has its sources in Central Brazil, where the river flows inside the valley and goes through a marked difference in elevation, from 800 to 350 m a.s.l. The middle Araguaia is a long river stretch (ca. 1,160 km) with low declivity (300 to 150 m a.s.l.), which favors the formation of floodable areas. This section holds the largest fluvial island on the planet, the Bananal Island (ca. 20,000 km²), surrounded by the Araguaia and Javaés rivers. The lower Araguaia, with ca. 500 km, is a lowland river (150 to 90 m a.s.l.) with a meandering channel, rapids, and islands, which flows towards the Tocantins River. Along its course, the main tributary rivers are: Peixe, Garças, Caiapó, Vermelho, Cristalino, das Mortes, and Javaés.

The expansion of human activities has impacted both rivers (Fig. 1), notably agriculture (Trigueiro et al., 2020), aquaculture (Lima et al., 2018), hydropower (Winemiller et al., 2016), and the use of water resources (Daga et al., 2020), associated with changes in land cover, river fragmentation, and the expansion of irrigated agriculture (Castello et al., 2013; Latrubesse et al., 2019; Pelicice et al., 2021). Currently, about 42% of the original vegetation has been removed or altered (Pelicice et al., 2021), a process that has accelerated in the last decade. The construction of hydropower dams has impacted the Tocantins River and its tributaries (Winemiller et al., 2016; Akama, 2017); the main channel is regulated by seven large dams (Fig. 1), which created large impoundments and changed the natural flow regime, causing multiple and persistent impacts on the fish fauna (Araújo et al., 2013; Perônico et al., 2020; Pereira et al., 2021). In the Araguaia River, the fast expansion of agriculture has changed the landscape, increasing water deficits, siltation, and contamination by hazardous pesticides (Scaramuzza et al., 2017; Latrubesse et al., 2019; Lima-Junior et al., 2024; Teixeira et al., 2024).

The fish fauna. The Tocantins-Araguaia basin flows into the Amazon estuary near Belém (Pará State). Although the basin has a particular geological origin and flow/sediment dynamics, it shares some fish species with other Amazonian tributaries (Ferreira et al., 2011; Dagosta, de Pinna, 2017; Orsi et al., 2018). Recent studies compiled about 751 species until 2020 (Dagosta, de Pinna, 2019; Chamon et al., 2022), and many others described more species recently (e.g., Deprá et al., 2021; Ota et al., 2021; Chamon, Fichberg, 2022; Soares et al., 2023); several taxa remain undescribed (e.g., Aloísio et al., 2005; Lucinda et al., 2007; Lima et al., 2021). The basin has high levels of fish endemism (Hubert, Renno, 2006; Abell et al., 2008; Dagosta, de Pinna, 2019), with approximately 30% of its fauna being endemic (Chamon et al., 2022).

Fish with migratory behavior have been reported to the basin (Neuberger et al., 2008; Barthem et al., 2017; Orsi et al., 2018). The ecology and behavior of migratory fishes, however, remain poorly known, with information limited to some fish with commercial value (Carvalho, Mérona, 1986; Mérona et al., 2010), or derived from other Amazonian systems (Duponchelle et al., 2021; Herrera-R et al., 2024). In the absence of long-term monitoring and large-scale studies, current knowledge remains deficient and tentative, lacking specific data, broad synthesis, or even species lists. Few studies have focused on reproductive dynamics. In the Araguaia River, a recent study showed that fish (including migratory species) reproduce mainly during the flood period, using tributaries and the main channel as spawning sites and nursery grounds (Carnicer et al., 2023). In the Tocantins River, migratory fish also reproduce during the wet season (Medeiros et al., 2008), but eggs and larvae have been observed mainly in the main channel of free-flowing sections (Pinto et al., 2008).

Data collection. To characterize the taxonomic and functional diversity of migratory fishes in the Tocantins-Araguaia basin, the present study followed a methodology articulated in four sequential steps (Fig. 2).

FIGURE 2| Methodology used (four steps) to identify potamodromous fishes in the Tocantins-Araguaia Basin, generating data to assess taxonomic and functional diversity.

– Step 1: General species list. This step compiled a broad species list for the Tocantins-Araguaia basin, based on Dagosta, de Pinna (2019), and Chamon et al. (2022). All records found in these papers were consolidated into a general list, with the addition of species described after 2020. Furthermore, Eschmeyer’s Catalog of Fishes (Fricke et al., 2024) was consulted to confirm the validity of the species. The procedure cataloged 761 species, 16 orders, and 51 families, with 229 species considered endemic (Tab. S1).

– Step 2: Potential potamodromous species. From the general species list (Step 1), potential potamodromous species were identified based on specialized literature devoted to migratory fishes in the Amazon region: Carolsfeld et al. (2003), Agostinho et al. (2008), Van Damme et al. (2011), Barthem et al. (2017), Doria et al. (2018), and Duponchelle et al. (2021). All species or genera reported as migratory were assigned as such. Some supposedly migratory species not mentioned by these references were also assigned as such. The procedure resulted in a list of 124 potentially potamodromous species for the Tocantins-Araguaia basin (Tab. S1).

– Step 3: List of potamodromous species. Based on the list of potential potamodromous species (Step 2), the migratory status of each species was checked. Each species was categorized according to a migration scale: (i) Sedentary, that is, non-migratory; (ii) short-distance migration (< 50 km), which implies longitudinal movements between river reaches and tributaries, or lateral movements toward floodplain areas; (iii) medium-distance migration (50 to 99 km), which involves longitudinal movements between river stretches and tributaries; (iv) long-distance migration (100 to 1000 km), which implies longitudinal movements between basin sections (upper, middle and lower); and (v) continental migrations (>1000 km), which implies longitudinal movements from estuaries to headwaters, including the movement across drainages. This classification was based on the same literature used in Step 2 (the most comprehensive to date), in addition to papers about the biology and ecology of Neotropical migratory fish, and the expertise of researchers involved in this research. After this classification, sedentary species and short-distance migrants (scale i and ii) were excluded from the list. We decided to exclude short-distance migrants because their displacements may be facultative or involve different motivations (e.g., dispersal, drifting), not necessarily associated with life cycles. Therefore, the final list intended to include only species that migrate over long distances (> 50 km) with the purpose to complete their life cycles, which resulted in a list of 77 species (Tab. S1).

– Step 4: Functional traits. A series of functional traits (Tab. S2) were assigned to the 77 selected fish species (Tab. S3), in order to characterize the functional diversity of potamodromous fishes. Trait assignment followed previous studies conducted in the basin (e.g., Agostinho et al., 2008; Vitorino Jr. et al., 2016; Perônico et al., 2020, Pereira et al., 2021), in addition to FishBase (Froese, Pauly, 2022). The chosen traits (Tab. S2) are directly related to habitat use, reproduction, trophic ecology, behavior and defense, representing niche dimensions that affect organism’s ecological performance (Winemiller et al., 2015). In total, we considered 16 functional traits divided in 50 trait-states (Tab. S2). The assignment of trait-states for each species is shown in Tab. S3.

Data analyses. To characterize the diversity of migratory fishes in the Tocantins-Araguaia basin, two matrices were generated: one with all migratory species (taxonomic, Tab. S1), and another with functional traits (functional, Tab. S3). Then, following objective (i), we built the list of potamodromous fishes in the basin. Following objectives (ii) and (iii), we calculated species richness for the basin, regions (upper Tocantins, lower Tocantins, and Araguaia), taxonomic families, and migration scale (medium, long and continental). Regions were restricted to the upper Tocantins (which included the middle section), lower Tocantins and Araguaia because we followed occurrence data as provided by Dagosta, de Pinna (2019), and Chamon et al. (2022). To evaluate changes in species composition between regions, we calculated beta diversity using the “beta” function of the BAT package (Cardoso et al., 2015), based on incidence data and Sorensen similarity.

Functional diversity was measured considering the functional traits assigned to each species. Following objectives (ii) and (iii), the functional diversity of migratory fishes was assessed by calculating functional richness (FRic). FRic represents the functional volume occupied by all species in a multidimensional space, obtained by extracting the first two axes of a Principal Coordinate Analysis (PCoA), generated from the dbFD function (Laliberté et al., 2014). The functional volume occupied by a set of species was measured using the “convex hull” approach (Villéger et al., 2008), which is based on the formation of polygons in a multidimensional space. Differences in the functional space (axis scores) occupied by the species were tested through Multivariate Analysis of Variance (MANOVA), considering regions, families and migratory scale as factors. Pairwise comparisons were conducted with the pairwise.perm.manova function, with 999 repetitions, using the RVAideMemoire package (Hervé, Hervé, 2020). Finally, variations in trait composition between regions were measured using the “beta” function of the BAT package (Cardoso et al., 2015), based on a trait incidence matrix and Sorensen similarity. Traits with no variation were excluded from all analyses (i.e., swimming, embryo development, and parental care).

All figures were drawn using the ggplot2 package (Wickham, 2011). All analyzes were conducted in R v. 4.3.2 (R Development Core Team, 2023). Statistical differences were considered at a level of significance of 5%.

Results​

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We consolidated a list of 77 potamodromous species in the Tocantins-Araguaia basin (Tab. 1), which include fish of different sizes, shapes, behavior, and lineages (Fig. 3). These fishes belonged to three orders, Clupeiformes (S = 02 species), Characiformes (S = 42) and Siluriformes (S = 33), 12 families, and 41 genera. Pimelodidae was the most species-rich family (S = 25), followed by Serrasalmidae (S = 15), and Curimatidae (S = 10); other families had less than three species (Tab. 1). Most species (S = 69) were widely distributed across the basin; eight were endemic, three threatened with extinction, and two non-natives (the tambaqui Colossoma macropomum and the pacu Piaractus mesopotamicus). Most species were classified as medium (S = 42) and long-distance (S = 32) migrants, and few as continental migrants (S = 03); this proportion was similar between regions (Fig. 4), excepting for continental migrants, recorded only in the lower Tocantins. We recorded 64 species in the upper and lower Tocantins, and 56 in the Araguaia; taxonomic composition was very similar between the three regions (Tab. 2).

TABLE 1 | List of potamodromous fishes in the Tocantins-Araguaia basin (S = 77), indicating their occurrence (1 = upper Tocantins; 2 = lower Tocantins; 3 = Araguaia), status (endemism, threat, origin), and migration scale.

Taxa	Regions			Status	Migration
	1	2	3
CLUPEIFORMES
PRISTIGASTERIDAE
Pellona castelnaeana Valenciennes, 1847	X	X	X		Long
Pellona flavipinnis (Valenciennes, 1837)	X	X			Long
CHARACIFORMES
ANOSTOMIDAE
Leporinus fasciatus (Bloch, 1794)	X		X		Medium
Leporinus friderici (Bloch, 1794)	X	X	X		Medium
Megaleporinus trifasciatus (Steindachner, 1876)	X	X	X		Long
BRYCONIDAE
Brycon falcatus Müller & Troschel, 1844	X	X	X		Long
Brycon gouldingi Lima, 2004	X	X	X	Endemic, Threatened	Long
Brycon nattereri Günther, 1864	X		X		Medium
Salminus hilarii Valenciennes, 1850	X	X	X		Long
CURIMATIDAE
Curimata acutirostris Vari & Reis, 1995	X	X	X		Medium
Curimata cyprinoides (Linnaeus, 1766)	X	X	X		Medium
Curimata inornata Vari, 1989	X	X	X		Medium
Curimata ocellata Eigenmann & Eigenmann, 1889	X	X			Medium
Curimata vittata (Kner, 1858)		X			Medium
Curimatella alburnus (Müller & Troschel, 1844)		X			Medium
Curimatella dorsalis (Eigenmann & Eigenmann, 1889)	X	X	X		Medium
Curimatella immaculata (Fernández-Yépez, 1948)	X	X	X		Medium
Curimatopsis macrolepis (Steindachner, 1876)	X		X		Medium
Psectrogaster amazonica Eigenmann & Eigenmann, 1889	X	X	X		Medium
CYNODONTIDAE
Hydrolycus armatus (Jardine, 1841)	X	X	X		Long
Hydrolycus tatauaia Toledo-Piza, Menezes & Santos, 1999	X	X			Long
Rhaphiodon vulpinus Spix & Agassiz, 1829	X	X	X		Medium
HEMIODONTIDAE
Anodus orinocensis (Steindachner, 1887)	X	X	X		Medium
Argonectes robertsi Langeani, 1999	X	X	X		Medium
PROCHILODONTIDAE
Prochilodus nigricans Spix & Agassiz, 1829	X	X	X		Long
Semaprochilodus brama (Valenciennes, 1850)	X	X	X		Long
SERRASALMIDAE
Colossoma macropomum (Cuvier, 1816)	X	X		Non-native	Long
Mylesinus paucisquamatus Jégu & Santos, 1988	X	X	X	Endemic, Threatened	Medium
Myleus setiger Müller & Troschel, 1844	X	X	X		Medium
Myloplus arnoldi Ahl, 1936	X		X		Medium
Myloplus asteria (Müller & Troschel, 1844)	X	X	X		Medium
Myloplus nigrolineatus Ota, Machado, Andrade, Collins, Farias & Hrbek, 2020		X			Medium
Myloplus rubripinnis (Müller & Troschel, 1844)		X	X		Medium
Myloplus schomburgkii (Jardine, 1841)	X	X	X		Medium
Myloplus torquatus (Kner, 1858)	X	X	X		Medium
Mylossoma duriventre (Cuvier, 1818)	X				Medium
Mylossoma unimaculatum (Steindachner, 1908)	X	X	X	Endemic	Medium
Piaractus brachypomus (Cuvier, 1818)	X	X	X		Long
Piaractus mesopotamicus (Holmberg, 1887)	X			Non-native	Long
Tometes ancylorhynchus Andrade, Jégu & Giarrizzo, 2016	X	X	X		Long
Tometes siderocarajensis Andrade, Machado, Jégu, Farias & Giarrizzo, 2017		X			Long
TRIPORTHEIDAE
Triportheus albus Cope, 1872	X	X	X		Medium
Triportheus auritus (Valenciennes, 1850)	X	X	X		Medium
Triportheus trifurcatus (Castelnau, 1855)	X	X	X	Endemic	Medium
SILURIFORMES
AUCHENIPTERIDAE
Ageneiosus inermis (Linnaeus, 1766)	X	X	X		Medium
Ageneiosus lineatus Ribeiro, Rapp Py-Daniel & Walsh, 2017		X			Medium
Ageneiosus ucayalensis Castelnau, 1855	X	X	X		Medium
Ageneiosus vittatus Steindachner, 1908		X			Medium
DORADIDAE
Lithodoras dorsalis (Valenciennes, 1840)	X				Medium
Megalodoras uranoscopus (Eigenmann & Eigenmann, 1888)	X	X	X		Long
Oxydoras niger (Valenciennes, 1821)	X	X	X		Long
Pterodoras granulosus (Valenciennes, 1821)	X	X	X		Long
PIMELODIDAE
Aguarunichthys tocantinsensis Zuanon, Rapp Py-Daniel & Jégu, 1993	X	X	X	Endemic, Threatened	Long
Brachyplatystoma filamentosum (Lichtenstein, 1819)	X	X	X		Long
Brachyplatystoma platynemum Boulenger, 1898		X			Continental
Brachyplatystoma rousseauxii (Castelnau, 1855)		X			Continental
Brachyplatystoma vaillantii (Valenciennes, 1840)		X			Continental
Hemisorubim platyrhynchos (Valenciennes, 1840)	X	X	X		Long
Hypophthalmus marginatus Valenciennes, 1840	X	X	X		Long
Phractocephalus hemioliopterus (Bloch & Schneider, 1801)	X	X	X		Long
Pimelodina flavipinnis Steindachner, 1876	X	X	X		Medium
Pimelodus albofasciatus Mees, 1974	X		X		Medium
Pimelodus blochii Valenciennes, 1840	X	X	X		Medium
Pimelodus luciae Rocha & Ribeiro, 2010		X		Endemic	Medium
Pimelodus ornatus Kner, 1858	X	X	X		Medium
Pimelodus quadratus Lucinda, Ribeiro & Lucena, 2016	X		X	Endemic	Medium
Pimelodus speciosus Costa e Silva, Ribeiro, Lucena & Lucinda, 2018	X		X	Endemic	Medium
Pimelodus tetramerus Ribeiro & Lucena, 2006	X	X	X		Medium
Pinirampus pirinampu (Spix & Agassiz, 1829)	X	X	X		Long
Platynematichthys notatus (Jardine, 1841)		X			Long
Platystomatichthys sturio (Kner, 1858)		X			Medium
Pseudoplatystoma fasciatum (Linnaeus, 1766)	X				Long
Pseudoplatystoma punctifer (Castelnau, 1855)	X		X		Long
Pseudoplatystoma reticulatum Eigenmann & Eigenmann, 1889	X				Long
Sorubim lima (Bloch & Schneider, 1801)	X	X	X		Long
Sorubimichthys planiceps (Spix & Agassiz, 1829)	X	X	X		Long
Zungaro zungaro (Humboldt, 1821)	X	X	X		Long

FIGURE 3| Potamodromous fishes from the Tocantins-Araguaia Basin. Characiformes: 1 = Hydrolycus armatus; 2 = Brycon falcatus; 3 = Semaprochilodus brama; 4 = Triportheus trifurcatus; 5 = Tometes siderocarajensis; 6 = Leporinus friderici. Siluriformes: 7 = Oxydoras niger; 8 = Ageneiosus inermis; 9 = Hemisorubim platyrhynchos; 10 = Platynematichthys notatus; 11 = Aguarunichthys tocantinsensis; 12 = Pseudoplatystoma punctifer; 13 = Sorubimichthys planiceps; 14 = Pimelodus albofasciatus; 15 = Brachyplatystoma filamentosum. Fish size is not to scale. Credits: Thiago N. S. Campos (1, 2, 4, 6-9, 12, 14), Lucas G. M. Frota (3), and Anderson B. Soares (5, 10, 11, 13, 15).

FIGURE 4| Number of potamodromous species in the three studied regions (upper and lower Tocantins, and Araguaia), considering the migration scale.

TABLE 2 | Taxonomic (species, lower triangle) and functional (traits, upper triangle) similarity in the composition of migratory fishes between the studied regions: upper and lower Tocantins, and Araguaia.

Region	Upper Tocantins	Lower Tocantins	Araguaia
Upper Tocantins	1	0.992	1
Lower Tocantins	0.796	1	0.8
Araguaia	0.916	0.992	1

The functional volume occupied by potamodromous fishes was similar between regions (Fig. 5A), indicating high similarity in trait composition; this pattern was confirmed by Sorensen similarity (Tab. 2) and MANOVA (F = 0.34, df = 2, p = 0.9). FRic values ​​were higher in the lower Tocantins (197.73), followed by the upper Tocantins (183.35) and Araguaia (182.99). Taxonomic families occupied a different functional space (Fig. 5B), indicating functional complementarity (MANOVA: F = 264.62, df = 11, p < 0.0001); pairwise comparisons showed that only Pimelodidae and Doradidae occupied similar functional spaces (Tab. S4). Pimelodidae occupied the largest functional space, but all families showed some intra-group variation. The functional space also differed between migratory scales (MANOVA: F = 110.30, df = 2, p < 0.0001; Fig. 5C).

FIGURE 5| Functional space (FRic) occupied by potamodromous fishes, considering the three regions investigated (A), taxonomic families (B) and migration scale (C).

All species presented carangiform swimming, external embryo development, and absence of parental care (Tab. 3). Furthermore, most species had maximum length greater than 20 cm, laterally or dorsally compressed bodies, no dermal plates, furcate caudal fin, and external fecundation. However, some traits were variable, such as the presence of barbels and spikes (present in some Siluriformes), mouth position and biting mechanics, feeding ecology, trophic position, and habitat use (Tab. 3).

TABLE 3 | Percentage of species classified in each trait-state.

Traits	%		Traits	%
1. Length (cm)		9. Mouth position
> 20	16.9		Terminal	48.1
20.1 – 40	41.6		Supraterminal	3.9
40.1 – 60	11.7		Subterminal	27.3
< 60.1	29.9		Inferior	20.8
2. Body shape		10. Feeding
Anguilliform	0.0		Detritivore	15.6
Elongated	0.0		Herbivore	10.4
Fusiform/cylindrical	7.8		Planktivore	2.6
Dorsoventral compression	35.1		Carnivore	7.8
Lateral compression	37.7		Piscivore	26.0
Dorsoventral compression (rounded)	0.0		Omnivore	37.7
Lateral compression (rounded)	19.5		11. Trophic level
3. Swimming		2 a 2.9		39.0
Anguilliform	0.0		3 a 3.9	22.1
Carangiform	100		4 a 4.9	27.3
Labriform	0.0		Na	11.7
Rajiform	0.0		12. Fertilization
Gymnotiform	0.0		Internal	5.2
4. Caudal fin			External	94.8
Emarginate	32.5		13. Embryo development
Furcate	67.5		Internal	0.0
5. Spikes		External		100
Present	58.4		14. Parental care
Absent	41.6		Present	0.0
6. Plates		Absent		100.0
Present	5.2		15. Migration
Absent	94.8		Medium	54.5
7. Barbels		Long		41.6
Present	39.0		Continental	3.9
Absent	61.0		16. Habitat
8. Mouth mechanics		Benthonic		33.8
Bite	36.4		Pelagic	26.0
Suction	48.1		Benthopelagic	40.3
Scrapper	15.6

Discussion​

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This is the first broad assessment about potamodromous fishes from the Tocantins-Araguaia basin. Of the 761 fish species recorded in this basin (Dagosta, de Pinna, 2019; Chamon et al., 2022), we identified 77 as potamodromous (ca. 10%, including two non-natives). Potamodromous fishes are widely distributed across the globe, characterized by performing mid to long-distance movements across the river networks to complete their life cycles (Lucas, Baras, 2001; Carolsfeld et al., 2003; Dean et al., 2022; Herrera-R et al., 2024). Our results showed that this group is especially diverse in the Tocantins-Araguaia basin, in taxonomic and functional terms. It is worth noting that this is the first synthesis conducted in the basin, based on information available in the literature, still incomplete, and fragmented. More studies are needed to further address biodiversity shortfalls (i.e., Linnean, Wallacean, and Raunkieran), especially to uncover basic biological aspects, migratory patterns, and population dynamics. The acquisition of more data is necessary to validate the species list, updating distribution patterns and the migratory status of species.

The high diversity of potamodromous fishes mirrors the high diversity found in the Tocantins-Araguaia basin, a common pattern to large Amazonian rivers (Jézéquel et al., 2020). The Tocantins-Araguaia basin is home to ca. 30% of all species recorded in the Amazon region (2,716 species; Dagosta, de Pinna, 2019), and its migratory fauna represents ca. 35% of all migratory species recorded in the region (223 species; Herrera-R et al., 2024). The vast drainage network of the Tocantins-Araguaia basin (ca. 770,000 km²), and the presence of different habitats (e.g., river channels, floodplains, large tributaries, streams), must also favor the maintenance of migratory fishes, which include species with different behaviors and ecological needs (Herrera-R et al., 2024). One important finding was the wide spatial distribution of species, with a few restricted to the upper or lower Tocantins. Furthermore, few migratory species were classified as endemic (eight, ca. 10%), contrasting with the high levels of endemism of the Tocantins-Araguaia basin (ca. 30%). These results indicate low beta diversity at regional scales, i.e., intra-basin and between Amazonian drainages. It is expected considering the dispersal potential of potamodromous fishes, as well as their life cycle, which involves the use of different habitats in the riverscape.

The 77 potamodromous species belonged to three orders (Clupeiformes, Characiformes, and Siluriformes) and 12 families, with most species classified as medium (54.5%) and long-distance (41.6%) migrants. Pimelodidae, Serrasalmidae, and Curimatidae summed most species – a common pattern observed in other Neotropical rivers (Carolsfeld et al., 2003; Herrera-R et al., 2024). Pimelodidae includes catfishes of different sizes and migratory behaviors, which perform mid-distance (e.g., Pimelodus), long-distance (e.g., Pseudoplatystoma), and continental migrations (e.g., Brachyplatystoma). Some large catfishes perform the longest known migration within freshwaters, involving thousands of kilometers between spawning and nursery sites in the Amazon system. Yet, they were restricted to the lower Tocantins, probably because Tucurui Dam, in the lower Tocantins, blocked access to upstream sections of the basin. In fact, old fishers have reported the presence of B. rousseouxii in the upper Tocantins in periods that preceded hydropower development (Santos, Pelicice, in press), constituting evidence that goliath catfishes dispersed across the Tocantins-Araguaia basin in pristine conditions. The basin was not a spawning ground according to previous research (Barthem et al., 2017), and probably worked as a feeding site. Serrasalmidae is a group of rounded fish characterized by high taxonomic and functional diversity in the Amazon (Andrade et al., 2019); in the Tocantins-Araguaia basin, these fish probably perform mid and long-distance migrations, but this family also includes sedentary and short-distance migrants (e.g., Serrasalmus). Curimatidae is another diverse family, composed of mid-sized detritivorous fish that form large aggregations during migrations, usually inhabiting river channels and floodplains (Herrera-R et al., 2024), where they serve as prey for large predatory fish (Montaña et al., 2011).

Ecological information about potamodromous fishes from the Tocantins-Araguaia Bains remains lacking, particularly data on migration routes, timing, spawning sites, and nursery areas. Based on data from other South American basins, we offer some speculation. Mid-distance (e.g., Curimatidae, Hemiodontidae, Serrasalmidae and Pimelodidae) and some long-distance migrants (e.g., Prochilodus nigricans) probably complete their life cycle within river stretches, forming regional sub-populations, with periodic migrations between river segments, tributaries, and floodplain areas (e.g., Lopes et al., 2019; Perini et al., 2021; Herrera-R et al., 2024). Long-distance migrants (e.g., Semaprochilodus brama, Piaractus brachypomus, Pseudoplatystoma fasciatum, Zungaro zungaro) probably perform up-downstream movements between lower, middle and upper sections, using tributaries as spawning sites (e.g., Agostinho et al., 2003; Sato, Godinho, 2003; Makrakis et al., 2012). Different recruitment dynamics are expected between the Tocantins and Araguaia rivers, because these systems have contrasting environmental conditions. The Tocantins River flows substantially channelized with little floodplain development (Ribeiro et al., 1995), which poses constraints to fish recruitment, probably involving the use of alternative habitats, such as river confluences and backwaters (e.g., Silva et al., 2020; Pachla et al., 2022). In fact, in free-flowing conditions, eggs and larvae have been recorded mainly in the main channel (Pinto et al., 2008). The Araguaia River, on the other hand, is home to a large floodplain system (i.e., Bananal Island; Latrubesse, Stevaux, 2002), a type of environment that provides nursery habitats for migratory fishes (e.g., Agostinho et al., 2004). In the upper and middle Araguaia, eggs and larvae have been recorded both in tributaries and in the main channel (Carnicer et al., 2023), probably drifting towards the floodplain area located downstream. In pristine conditions, some migratory fishes probably migrated between the Araguaia and Tocantins rivers (Carvalho, Mérona, 1986), involving also movements towards the Amazon estuary and other sub-basins. The former record of goliath catfishes in the upper Tocantins (i.e., B. rousseauxii; Santos, Pelicice, in press) supports the idea that some migratory fish migrated between different parts of the system. All these patterns, however, are difficult to assess, given the current fragmentation imposed by hydroelectric dams constructed along the Tocantins River, and the consequent isolation of the Araguaia River (which remains free from dams along its main channel). Future studies must consider the existence of isolated sub-populations and regional recruitment dynamics.

Functional diversity was similar between regions, reflecting the high similarity in taxonomic composition. Moreover, some traits were widely shared among species, such as medium to large size, compressed body (laterally or dorsally), no dermal plates, carangiform swimming, furcated fins, external fertilization and development, and absence of parental care. These traits are common among Neotropical potamodromous fishes (e.g., Agostinho et al., 2003; Sato, Godinho, 2003; Zaniboni-Filho, Schulz, 2003), and seem to represent a broad functional characterization of this group. However, we observed significant variation in the functional space occupied by each species, with a clear segregation among families, indicating functional variation and complementarity. Almost all trait-states showed some variation, particularly the presence of barbels and spikes (i.e., some Siluriformes), mouth position, biting mechanics, feeding ecology, trophic position, and habitat use; functional variation was also observed within families (e.g., Pimelodidae). In addition, functional richness was higher for mid and long-distance migrants, possibly associated with a diversity of needs, behaviors, and strategies, as these groups may use different migratory routes, perform longitudinal and lateral migration, and use different spawning and nursery sites (Godinho, Kynard, 2009; Makrakis et al., 2012; Herrera-R et al., 2024). These results therefore revealed that potamodromous fishes share several common traits, but trait composition is variable, indicating they have developed different solutions to survive and reproduce. Although the functional diversity of Neotropical fishes is well recognized (Toussaint et al., 2016; Vitule et al., 2016), functional approaches have not focused on migratory fishes, with a strong bias toward stream fishes (e.g., Carvalho, Tejerina-Garro, 2015; Teresa et al., 2015; Borba et al., 2021). Future studies must investigate the relationship between functional traits and aspects of the life cycle, for example, whether traits are related to migratory behavior (distance, routes, timing) and critical habitats. Such understanding would allow the prediction of behavioral aspects, habitat needs and human impacts.

The criteria used to classify migratory fish deserves some consideration, as there are different views in the literature. Traditionally, migratory fish have been those that perform long longitudinal movements along the river (e.g., Agostinho et al., 2003; Makrakis et al., 2012; Soares et al., 2022), but recent studies have adopted a broader view by including short-distance and lateral movements (Duponchelle et al., 2021; Herrera-R et al., 2024). In the present work, we adopted an intermediate approach, considering only species that perform migrations along the river (> 50 km), which includes mid-distance migrants, but excludes short-distance migrants (e.g., some Anostomidae, Serrassalmidae, Gymnotiformes), whose migratory status may be controversial. In the case of the Tocantins-Araguaia basin, a broader criterion (e.g., Herrera-R et al., 2024) would change substantially the species list, considering that our initial compilation gathered 124 species. Moreover, primary data are absent or incomplete for many species, so future studies must reassess and validate our classification, which was based on the best available information, but significantly limited. Multiple approaches are necessary, including telemetry techniques, otolith chemistry, eggs and larvae distribution, and fishery catches (e.g., Barthem et al., 2017). It must be considered that migration is a complex phenomenon, as Neotropical fishes evolved in lotic environments (Albert et al., 2020), where dispersion and migratory movements are common features, even among typically sedentary (e.g., cichlids or Arapaima gigas; Hoeinghaus et al., 2003; Castello, 2008) or small-sized fish (e.g., Astyanax or Trichomycterus; Miranda-Chumacero et al., 2015; Vidotto-Magnoni et al., 2021). This situation highlights the high diversity of migratory behaviors among Neotropical potamodromous fish, an aspect that remains poorly known, which contrasts with well-known migratory fish from other regions (Dean et al., 2022).

The conservation of migratory fishes is a matter of preoccupation, as these fishes have declined on a global scale (Deinet et al., 2020; Huang, Li, 2024). The conservation status of migratory fishes in the Tocantins-Araguaia basin raises concerns, considering the current scenario of environmental degradation induced by river regulation, deforestation, water diversion and other stressors (Latrubesse et al., 2019; Pelicice et al., 2021; Swanson, Bohlman, 2021; Chamon et al., 2022). Currently three endemic migratory species are threatened with extinction (i.e., Aguarunichthys tocantinsensis, Brycon gouldingi, and Mylesinus paucisquamatus), but the situation is probably worse, considering the lack of monitoring and assessments. In fact, populations have declined or even disappeared from some reaches (Perônico et al., 2020; Pereira et al., 2021), with effects on small-scale artisanal fisheries (Santos, Pelicice, in press). In the current scenario, fish movements are substantially blocked by hydroelectric dams that isolated the Araguaia River and fragmented the upper, middle and lower stretches of the Tocantins River (Winemiller et al., 2016; Akama, 2017). Moreover, both rivers have been progressively impacted by changes in land use, the expansion of irrigated agriculture, and contamination (Scaramuzza et al., 2017; Sano et al., 2019; Trigueiro et al., 2020; Lima-Junior et al., 2024). Management actions have been controversial, as installed fishways (ladders) have proven to be ineffective or prejudicial (Agostinho et al., 2011; Pelicice, Agostinho, 2012). In this scenario, the maintenance of river networks, flow regimes and habitats must be priority; in particular, the preservation of fluvial remnants in the Tocantins River and the floodplain area on the Bananal Island.

Acknowledgments​

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The authors thank the Universidade Federal do Tocantins (UFT), the Núcleo de Estudos Ambientais (Neamb) and the Programa de Pós-Graduação em Biodiversidade, Ecologia e Conservação (PPGBec) for providing infrastructure and support. Financial supportwas received from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), by providing scholarship for TNSC (master thesis) and research grants for FMP (process number 312256/2020–5).

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Authors

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Thiago Nascimento da Silva Campos¹ , Hasley Rodrigo Pereira², Phâmela Bernardes Perônico³, Carine Cavalcante Chamon⁴, Philip Teles Soares⁵ and Fernando Mayer Pelicice⁴

^[1]    Programa de Pós-Graduação em Biodiversidade, Ecologia e Conservação (PPGBec), Universidade Federal do Tocantins (UFT), 77500-000 Porto Nacional, TO, Brazil. (TNSC) thiago_tnsc@hotmail.com (corresponding author).

^[2]    Secretaria de Estado da Educação de Goiás, 5ª Av., Quadra 71, 212, 74643-030 Goiânia, GO, Brazil. (HRP) hasleybio08@gmail.com.

^[3]    Universidade Estadual de Goiás (UEG), Laboratório de Biogeografia e Ecologia Aquática, 75132-903 Anápolis, GO, Brazil. (PBP) phamelabernardes@gmail.com.

^[4]    Núcleo de Estudos Ambientais (Neamb), Programa de Pós-Graduação em Biodiversidade, Ecologia e Conservação (PPGBec), Universidade Federal do Tocantins (UFT), Rua 3, Quadra 17, Jardim dos Ipês, 77500-000 Porto Nacional, TO, Brazil. (CCC) carinechamon@mail.uft.edu.br. (FMP) fmpelicice@mail.uft.edu.br.

^[5]    Instituto Nacional de Ciência e Tecnologia em Ecologia, Evolução e Conservação da Biodiversidade (INCT EECBio), Universidade Federal de Goiás (UFG), Avenida Esperança, s/n, Campus Samambaia, 74690-900 Goiânia, GO, Brazil. (PTS) philip13ph@gmail.com.

Authors’ Contribution

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Thiago Nascimento da Silva Campos: Data curation, Formal analysis, Investigation, Methodology, Software, Writing-original draft, Writing-review and editing.

Hasley Rodrigo Pereira: Formal analysis, Investigation, Methodology, Supervision, Validation, Visualization, Writing-review and editing.

Phâmela Bernardes Perônico: Investigation, Methodology, Supervision, Validation, Writing-review and editing.

Carine Cavalcante Chamon: Validation, Visualization, Writing-review and editing.

Philip Teles Soares: Formal analysis, Investigation, Methodology, Software, Writing-review and editing.

Fernando Mayer Pelicice: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing-original draft,

Ethical Statement​

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Not applicable.

Competing Interests

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The author declares no competing interests.

How to cite this article

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Campos TNS, Pereira HR, Perônico PB, Chamon CC, Soares PT, Pelicice FM. Diversity of potamodromous fishes in the Tocantins-Araguaia basin. Neotrop Ichthyol. 2025; 23(1):e240098. https://doi.org/10.1590/1982-0224-2024-0098

Copyright​

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Distributed under

Creative Commons CC-BY 4.0

© 2025 The Authors.

Diversity and Distributions Published by SBI

Accepted December 12, 2024 by Paulo Pompeu

Submitted September 26, 2024

Epub February 10, 2025