Abstract

This study presents a survey of small-stream fish species from the Purus-Madeira interfluve, collected in four streams near Humaitá on the highway BR-319. The results reveal a rich and diversified ichthyofauna with 3016 collected individuals distributed in 84 species, six orders, 25 families, and 60 genera. Of all the specimens collected, the Characiformes was the most representative, with eight families, 26 genera, and 42 species, followed Siluriformes, with nine families, 20 genera, and 23 species. In terms of families, Characidae had the highest number of species (25), followed by Loricariidae (9), and Cichlidae (8). Among the 95 captured species,s 11 are the first records for the region, evidencing a high diversity in these environments. Of the 84 species recorded in this study, 15 have not been assessed by the IUCN, while the remaining 62 include 23 listed as Least Concern (LC), three as data deficient (DD), and one as Near Threatened (NT). The southeastern Amazon region still has few fish surveys, especially in the region comprising the Purus-Madeira Interfluve, which highlights the importance of surveys to fill gaps and understand the biodiversity distribution patterns in the region.

Keywords
Checklist; fishes; BR-319; Amazonian; biodiversity; conservation

Resumo

Este estudo apresenta um levantamento das espécies de peixes de pequenos riachos do interflúvio Purus-Madeira, coletadas em quatro riachos perto de Huimaitá na rodovia BR-319. Os resultados revelam uma ictiofauna rica e diversificada com 3016 indivíduos distribuídos em 84 espécies, seis ordens, 25 famílias e 60 gêneros. De todos os espécimes coletados, Characiformes foi a mais representativa, com oito famílias, 26 gêneros e 42 espécies, seguida da Siluriformes, com 9 famílias, 20 gêneros e 23 espécies. Em termos de famílias, Characidae apresentou o maior número de espécies (25), seguida de Loricariidae (9) e Cichlidae (8). Dentre as espécies capturadas, do total de 84 espécies, 11 são o primeiro registro da região, evidenciando uma alta diversidade nesses ambientes. Das 84 espécies registradas neste trabalho, 15 não foram avaliadas pela IUCN, 63 listadas como Menos Preocupante (LC), quatro como Deficientes em Dados (DD) e uma como Quase Ameaçada (NT). A região sudoeste da Amazônia ainda conta com poucos levantamentos de peixes, principalmente na região que compreende o Interflúvio Purus-Madeira, por isso é importante realizar levantamentos para preencher lacunas de coletas e compreender padrões de distribuição da biodiversidade da região.

Palavras-chave
Lista de espécies; peixes; BR-319; Amazônia; conservação; biodiversidade

Introduction

Studies of small Amazonian streams have increased in the last two decades (Mendonça et al., 2005MENDONÇA, P.F., MAGNUSSON, E.W. & ZUANON, J. (2005). Relationships Between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia; Copeia 2005:751–764.; Barros et al., 2011BARROS, D.F., ZUANON, J., MENDONÇA, F.P., SANTO, H.M.V.E., GALUCH, A.V. & ALBERNAZ, A.L.M. (2011). The fish fauna of streams in the Madeira-Purus interfluvial region, Brazilian Amazon. Check List. 7:768–773.; Benone et al., 2017BENONE, N.L., LIGEIRO, R., JUEN, L. & MONTAG, L.F.A. (2017). Role of environmental and spatial processes structuring fish assemblages in streams of the eastern Amazon. Marine and Freshwater Research, 69(2):243–252.; Leitão et al., 2018LEITÃO, R.P., ZUANON, J., MOUILLOT, D., LEAL, C.G., HUGHES, R.M., KAUFMANN, P.R., VILLÉGER, S., POMPEU, P.S., KASPER, D., PAULA, F.R., FERRAZ, S.F.B. & GARDNER, A. (2018). Disentangling the pathways of land use impacts on the funcitonal structure of fish assemblages in Amazon streams. Ecography, 41:219–232, 2018. https://doi.org/10.1111/ecog.02845.
https://doi.org/10.1111/ecog.02845... ; Stegmann et al., 2019; Benone et al., 2020BENONE, N.L., LEAL, C.G., DOS SANTOS, L.L., MENDES, T.P., HEINO, J. & MONTAG, L.F.A. (2020). Unravelling patterns of taxonomic and functional diversity of Amazon stream fish. Aquatic Sciences, 82(4):1–11.), and show that the ichthyofauna in these environments is composed by at least 50% of medium to small-sized individuals (up to 150 mm length), and with high indices of endemism (Castro, 2021CASTRO, R.M.C. (2021). Evolução da ictiofauna de riachos sul-americanos (Castro, 1999) revisitado após mais de duas décadas. Oecologia Australis, 25(2):231–245. https://doi.org/10.4257/oeco.2021.2502.02.
https://doi.org/10.4257/oeco.2021.2502.0... ).

Small streams in forest areas are particularly vulnerable to human occupation (e.g. Dias et al., 2009DIAS, M.S., MAGNUSSON, W.E. & ZUANON, J. (2009). Effects of Reduced-Impact Logging on Fish Assemblages in Central Amazonia. Conservation Biology 24(1):278–286.), especially considering the high endemic-species diversity in this type of environment (Albert et al., 2011ALBERT, J.S., CARVALHO, T.P., PETRY, P., HOLDER, M.A., MAXIME, E.L., ESPINO, J. & REIS, R.E. (2011). Aquatic biodiversity in the Amazon: habitat specialization and geographic isolation promote species richness. Animals, 1(2):205–241.). However, studies of the composition and distribution of fish assemblages of small streams in the region affected by the Álvaro Maia Federal Highway (BR-319) are restricted to a few stretches of the interfluve or in streams close to big rivers (Barros et al., 2011BARROS, D.F., ZUANON, J., MENDONÇA, F.P., SANTO, H.M.V.E., GALUCH, A.V. & ALBERNAZ, A.L.M. (2011). The fish fauna of streams in the Madeira-Purus interfluvial region, Brazilian Amazon. Check List. 7:768–773.; Queiroz et al., 2013bQUEIROZ, L.J., TORRENTE-VILARA, G., OHARA, W.M., PIRES, T.H.S., ZUANON, J. & DORIA, C.R.C. (2013). Peixes do Rio Madeira. São Paulo: Dialeto Latin American Documentary: Vol. 1–3.; Vieira et al., 2016VIEIRA, F.G., MATSUZAKI, A.A., BARROS, B.S.F., OHARA, W.M., PAIXÃO, A.D.C., TORRENTE-VILARA, G., ZUANON, J. & DORIA, C.R.C. (2016). Catalogo de peixes da ESEC Cuniã.; Stegmann et al., 2019STEGMANN, L.F., LEITÃO, R.P., ZUANON, J. & MAGNUSSON, W.E. (2019). Distance to large rivers affects fish diversity patterns in highly dynamic streams of Central Amazonia. PloS One, 14(10), e0223880.). The lack of governance along the BR-319, a road that connects the city of Manaus, in Amazonas state, to the city of Porto Velho, in Rondônia state, is responsible for several socioenvironmental impacts (Fearnside et al., 2009FEARNSIDE, P.M. & GRAÇA, P.M.L.A. (2009). Transporte hidroviário por cabotagem como alternativa à Rodovia Manaus-Porto Velho (BR-319). Anais da IV Jornada de Seminários Internacionais sobre Desenvolvimento Amazônico, 3:437–441.; Andrade et al., 2021ANDRADE, M.B., FERRANTE, L. & FEARNSIDE, P.M. (2021). A rodovia BR-319 brasileira demonstra uma falta crucial de governança ambiental na Amazônia. Conservação Ambiental, 48(3):161–164.).

Located in the Purus-Madeira interfluve, its connection to the deforestation arch has generated opportunities for people to illegally occupy, deforest, and offer land for sale, including environmental protection areas (EPAs) and indigenous lands (Fearnside & Graça, 2009FEARNSIDE, P.M., GRAÇA, P.M.L.A., KEIZER, E.W.H., MALDONADO, F.D., BARBOSA, R.I. & NOGUEIRA, E.M. (2009). Modelagem de desmatamento e emissões de gases de efeito estufa na região sob influência da Rodovia Manaus-Porto Velho (BR-319). Revista Brasileira de Meteorologia 24(2):208–233. https://doi.org/10.1590/S0102-77862009000200009.
https://doi.org/10.1590/S0102-7786200900... ; Anjos et al., 2019ANJOS, M.R., MACHADO, N.G., PEDERSOLI, M.A., PEDERSOLI, N.R.B., BARROS, B.S., LOURENÇO, I.H. & BARREIROS, J.P. (2019). Survey of fish species from the Lower Roosevelt River, Southwestern Amazon basin. Biota Neotropica, 19(4):e20180717. https://doi.org/10.1590/1676-0611-BN-2018-0717.
https://doi.org/10.1590/1676-0611-BN-201... ; Ferrante et al., 2020FERRANTE, L., GOMES, M. & FEARNSIDE, P.M. (2020). Amazonian indigenous peoples are threatened by Brazil’s Highway BR-319. Land Use Policy, 94:104548.; Ferrante et al., 2021FERRANTE, L., DE ANDRADE, M.B.T., LEITE, L., JUNIOR, C.S., LIMA, M., JUNIOR, M.C. & FEARNSIDE, P.M. (2021). BR-319: O caminho para o colapso da Amazônia e a violação dos direitos indígenas. Amazônia Real, 23.). These protected areas are critical to biodiversity because they promote the conservation of the forest cover, a crucial factor in the ichthyological diversity (Castello et al., 2013CASTELLO, L., MCGRATH, D.G., HESS, L.L., COE, M.T., LEFEBVRE, P.A., PETRY, P. & ARANTES, C.C. (2013). The vulnerability of Amazon freshwater ecosystems. Conservation Letters, 6(4):217–229.; Lobón-Cerviá et al., 2015LOBÓN-CERVIÁ, J., HESS, L.L., MELACK, J.M. & ARAUJO-LIMA, C.A. (2015). The importance of forest cover for fish richness and abundance on the Amazon floodplain. Hydrobiologia, 750(1):245–255.; Arantes et al., 2017ARANTES, C.C., WINEMILLER, K.O., PETRERE, M., CASTELLO, L., HESS, L.L. & FREITAS, C.E. (2017). Relationships between forest cover and fish diversity in the Amazon River floodplain. Journal of Applied Ecology, 55(1):386–395.; Frederico et al., 2018FREDERICO, R.G., ZUANON, J. & DE MARCO JR, P. (2018). Amazon protected areas and its ability to protect stream-dwelling fish fauna. Biological Conservation, 219:12–19.; Barros et al., 2020BARROS, D.F., PETRERE-JR, M., LECOURS, V., BUTTURI-GOMES, D., CASTELLO, L. & ISAAC, V.J. (2020). Effects of deforestation and other environmental variables on floodplain fish catch in the Amazon. Fisheries Research, 230:105643.).

Small streams can be altered by anthropogenic impacts across watersheds (Leal et al., 2016LEAL, C.G., POMPEU, P.S., GARDNER, T.A., LEITÃO, R.P., HUGHES, R.M., KAUFMANN, P.R., ZUANON, J., PAULA, F.R., FERRAZ, S.F.B., THOMSON, J.R, MAC NALLY, R., FERREIRA, J. & BARLOW, J. (2016). Multi-scale assessment of human-induced changes to Amazonian instream habitats. Landscape Ecology, 31:1725–1745. https://doi.org/10.1007/s10980-016-0358-x.
https://doi.org/10.1007/s10980-016-0358-... ) and must be monitored frequently, especially when considering the occupational processes occurring in the interfluve region. Also, fishes are bioindicators that can provide excellent ecological answers since they are relatively easier to identify (at least as morphospecies) than other groups, have life cycles long enough to allow temporal comparisons, and are dependent on numerous biotic and abiotic factors (Mendonça et al., 2005MENDONÇA, P.F., MAGNUSSON, E.W. & ZUANON, J. (2005). Relationships Between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia; Copeia 2005:751–764.). Here, we present a list of fish species recorded from small streams along the Purus-Madeira interfluve to identify new occurrences and complement the assessments already undertaken along the interfluve, including new surveys near the southern extremity of the BR 319 highway.

Material and Methods

1.

Study area

The interfluve region of the Purus and Madeira Rivers, both tributaries of the Amazon River, is part of the Içá formation, which is constituted by tabular formations with wide fluvial terraces and weak draining incision, and probably originated in the Pleistocene (CPRM, 1997CPRM. (1997). Projeto de Zoneamento Ecológico-Econômico da Região Fronteiriça Brasil-Colômbia, Eixo Tabatinga-Apaporis. Tome II. CPRM, Brasília/Manaus.). The Purus-Madeira interfluve is approximately 800 km long and 150 km wide and holds a wide variety of habitats, including natural grasslands, upland and flooded forests (Rapp Py-Daniel et al., 2007PY-DANIEL, L.R., DEUS, C.P., RIBEIRO, O.M. & SOUSA, L.M. (2007). Peixes. In: Py-Daniel LR, Deus CP, Henriques AL, DM Pimpão, Ribeiro OM (Ed.). Biodiversidade do Médio Madeira: Bases científicas para propostas de conservação. Manaus: INPA. P. 89–125.; Campos, 2011CAMPOS, M.C.C. (2011). Caracterização e gênese de solos em diferentes ambientes fisiograficos na região sul do Amazonas. Editora da PUC Goiás, 112 pp.).

Original data was collected in PPBio modules 12 and 13 near Humaitá, Amazonas. Module 13 is located 10 km from the Humaitá township, and module 12 is located 40 km away (Table 1), adjoining the BR-319 – and inside a military area (Figure 1).

2.

Data collection

Specimens were collected under the SISBIO permanent license N° 29476-4, following the methodology proposed by Mendonça et al. (2005)MENDONÇA, P.F., MAGNUSSON, E.W. & ZUANON, J. (2005). Relationships Between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia; Copeia 2005:751–764., which consists of the active sampling of 50 m of a delimited part of the stream using fishnets with <3 mm mesh, and with an effort of 4 persons during one hour.

Seven collections were carried out over a period of three years in four small-streams from a Madeira River micro-basin. Four collections were made between 2018 and 2019 (Module 13), and three between 2019 and 2020 (Module 12). Initially, it was planned to have four collections in Module 12 as well. However, the COVID-19 pandemic made it impossible to carry out the fourth collection.

The collected individuals were euthanized with Eugenol, fixed in 10% formaldehyde, and stored in flasks with 70% ethanol. All captured specimens are deposited in the Laboratório de Ictiologia e Ordenamento Pesqueiro do Vale do Rio Madeira – LIOP, of the Universidade Federal do Amazonas – UFAM, Instituto de Educação, Agricultura e Ambiente – IEAA, in Humaitá, Amazonas State. The species’ threatened status was derived from the IUCN Red List of Threatened Species (IUCN, 2024), criteria available in https://www.iucnredlist.org/.

3.

Taxonomic identification

We separated, counted and identified the captured individuals to the lowest possible taxonomic level, using taxonomic keys and specialized literature (Weitzman 1960WEITZMAN, S.H. (1960). Further notes on the relationships and classification of the South American characid fishes of the subfamily Gasteropelecinae. Stanford Ichthyological Bulletin 7(4):217–239.; 1978WEITZMAN, S.H. (1978). Three new species of fishes of the genus Nannostomus from the Brazilian states of Pará and Amazonas (Teleostei: Lebiasinidae). Smithsonian Contributions to Zoology, 263:1–14.; Rosen & Rumney, 1978; Géry 1977Géry, J. (1977). Characoids of the World. Neptune: TFH Publications. 772 p.; 1993GÉRY, J. (1993). Description de trois espèces nouvelles du genre Iguanodectes (Pisces, Characiformes, Characidae), avec quelques données récentes sur les autres espèces. Revue française d’Aquariologie 19(4):97–105.; Kullander 1986KULLANDER, S.O. (1986). Cichlid fishes of the Amazon River drainage of Peru. Stockholm: Swedish Museum of Natural History. 431 p.; 1989KULLANDER, S.O. (1989). Description of a new Acaronia species from the Rio Orinoco and Rio Negro drainages. Zoologica Scripta, 18(3):447–452.; 1995KULLANDER, S.O. (1995). Three new cichlid species from southern Amazonia: Aequidens gerciliae, A. epae and A. michaeli. Ichthyological Exploration of Freshwaters, 6:149–170.; Vari and Ortega 1986VARI, R.P. & ORTEGA, H. (1986). The catfishes of the Neotropical family Helogenidae (Ostariophysi: Siluroidei). Smithsonian Contributions to Zoology 442:1–20.; Weitzman and Vari 1987WEITZMAN, S.H. & VARI, R.P. (1987). Two new species and a new genus of miniature characid fishes (Teleostei: Characiformes) from northern South America. Proceedings of The Biological Society of Washington, 100(3):640–652.; Burgess 1989BURGESS, W.E. (1989). An atlas of freshwater and marine catfishes. Neptune: TFH Publications. 784 p.; Kullander and Ferreira 1991KULLANDER, S.O. & FERREIRA, E.J.G. (1991). A new Aequidens species from the Rio Trombetas, Brasil, and redescription of Aequidens pallidus. Zoologica Scripta, 19(4):425–433.; Huber 1992HUBER, J.H. (1992). Rivulus: Ecobiogeography – Relationships. Laboratoire d’Ichtyologie general et appliquee. Paris: Museum National d’Histoire Naturelle. 572 p.; Vari 1992VARI, R.P. (1992). Systematics of the Neotropical Characiform genus Cyphocharax Fowler (Pisces, Ostariophysi). Smithsonian Contributions to Zoology 529:1–137.; Buckup 1993; Mago-Leccia 1994MAGO-LECCIA, F. (1994). Electric fishes of the continental waters of America. Caracas: Fundacion para el Desarrollo de las Ciencias Fisicas, Matematicas y Naturales. 206 p.; Reis 1997REIS, R.E. (1997). Revision of the Neotropical genus Hoplosternum (Ostariophysi: Siluriformes: Callichthyidae) with the description of two new genera and three new species. Ichthyological Exploration of Freshwaters 7:299–326.; Schaefer 1997SCHAEFER, S.A. (1997). The Neotropical cascudinhos: Systematics and biogeography of the Otocinclus catfishes (Siluriformes: Loricariidae). Proceedings of the Academy of Natural Sciences of Philadelphia, 148:1–120.; Zarske and Géry 1997ZARSKE, A. & GÉRY, J. (1997). Ein neuer Salmleraus Peru. Das Aquarium, 336:12–17.; Römer 2002RÖMER, U. (2002). Cichlid Atlas, Volume 1. Natural History of South American Dwarf Cichlids. Parts 1 and 2. Germany: Mergus, Melle. 1311 p.; Crampton et al., 2003CRAMPTON, W.G.R. & ALBERT, J.S. (2003). Redescription of Gymnotus coropinae (Gymnotiformes, Gymnotidae), an often misidentified species of Neotropical electric fish, with notes on natural history and electric signals. Zootaxa, 348:1–20.; Crampton and Albert 2003CRAMPTON, W.G.R., LOVEJOY, N.R. & ALBERT, J.S. (2003). Gymnotus ucamara: a new species of Neotropical electric fish from the Peruvian Amazon (Ostariophysi: Gymnotidae), with notes on ecology and electric organ discharges. Zootaxa, 277:1–18.; Armbruster, 2004ARMBRUSTER, J.W. (2004). Phylogenetic relationships of the suckermouth armored catfishes (Loricariidae) with emphasis on the Hypostominae and the Ancistrinae. Zoological Journal of the Linnean Society, 141:1–80.; Crampton et al., 2004CRAMPTON, W.G.R. & ALBERT, J.S. (2004). Redescription of Gymnotus coatesi (Gymnotiformes, Gymnotidae), a Rare Species of Electric Fish from the Lowland Amazon Basin, with Descriptions of Osteology, Electric Signals and Ecology. Copeia, 2004(3):525–533.; Crampton and Albert 2004CRAMPTON, W.G.R., HULEN, K.G. & ALBERT, J.S. (2004). Sternopygus branco: A new species of neotropical electric fish (Gymnotiformes: Sternopygidae) from the lowland Amazon basin, with descriptions of osteology, ecology, and electric organ discharges. Copeia, 2004(2):245–259.; Crampton et al., 2005CRAMPTON, W.G.R., THORSEN, D.H. & ALBERT, J.S. (2005). Three new species from a diverse, sympatric assemblage of the electric fish Gymnotus (Gymnotiformes: Gymnotidae) in the lowland Amazon Basin, with notes on ecology. Copeia 2005(1):82–99.; Lundberg 2005LUNDBERG, J.G. (2005). Gymnorhamphichthys bogardusi, a new species of sand knifefish (Gymnotiformes: Rhamphichthyidae) from the Rio Orinoco, South America. Annals of the South African Museum, 479:1–4.; Reis et al., 2005REIS, R.E., LE BAIL, P.Y. & MOL, J.H.A. (2005). New arrangement in the synonymy of Megalechis Reis, 1997 (Siluriformes: Callichthyidae). Copeia 2005(3):678–682.; Sousa and Py-Daniel 2005SOUSA, L.M. & PY-DANIEL, L.H.R. (2005). Description of two new species of Physopyxis and redescription of P. lyra (Siluriformes: Doradidae). Neotropical Ichthyology 3(4):625–636.; Zarske and Géry 2006ZARSKE, A. & GÉRY, J. (2006). Zur identität von Copella nattereri (Steindachner, 1876) einschließlich der Beschreibung einer neuen Art (Teleostei: Characiformes: Lebiasinidae). 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Zootaxa, 2577:57–68.; Queiroz et al., 2013aQUEIROZ, L.J., TORRENTE-VILARA, G., VIEIRA, F.G., OHARA, W.M., ZUANON, J. & DORIA, C.R. (2013). Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List. 9:540–548.; Zuanon et al., 2015ZUANON, J., MENDONÇA, F.P., ESPÍRITO-SANTO, H.M., DIAS, M.S., GALUCH, A.V. & AKAMA, A. (2015). Guia de Peixes da Reserva Ducke, Amazônia Central.INPA, Manaus, 154 pp.; Crampton et al., 2016CRAMPTON, W.G., SANTANA, C.D.D., WADDELL, J.C. & LOVEJOY, N.R. (2016). A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species. Neotropical Ichthyology, 14:e150146.).

Results

We captured 3016 individuals, distributed in six orders, 25 families, 60 genera, and 84 species (Table 2). Characiformes had the most species, totalizing 42 species distributed in eight families and 26 genera, mostly in the Characidae, which had 25 species. Siluriformes was the second most captured order, with 23 species distributed in nine families, and 20 genera, followed by Cichliformes, with nine species, and the Gymnotiformes, with eight species. Beloniformes and Synbranchiformes were the least captured orders with the lower species richness (Figure 2A).

In the module 13, Stream 4 had the highest species richness, with a total of 53 fish species recorded, followed by Stream 3, with 45 species. Fewer species were captured in module 12, , with 15 species in Stream 1 and 17 in Stream 2 (Figure 2B,C). Apistogramma agassizii, Gladioglanis conquistador, Hemigrammus ocellifer and Nannostomus eques were recorded in all the streams of this study.

Of the 84 captured species, 11 are the first record of occurrence (Figure 3) in the Purus-Madeira interfluve area for assessments made following the Mendonça et al. (2005)MENDONÇA, P.F., MAGNUSSON, E.W. & ZUANON, J. (2005). Relationships Between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia; Copeia 2005:751–764. method (Barros et al., 2011BARROS, D.F., ZUANON, J., MENDONÇA, F.P., SANTO, H.M.V.E., GALUCH, A.V. & ALBERNAZ, A.L.M. (2011). The fish fauna of streams in the Madeira-Purus interfluvial region, Brazilian Amazon. Check List. 7:768–773.; Queiroz et al., 2013aQUEIROZ, L.J., TORRENTE-VILARA, G., VIEIRA, F.G., OHARA, W.M., ZUANON, J. & DORIA, C.R. (2013). Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List. 9:540–548.,bQUEIROZ, L.J., TORRENTE-VILARA, G., OHARA, W.M., PIRES, T.H.S., ZUANON, J. & DORIA, C.R.C. (2013). Peixes do Rio Madeira. São Paulo: Dialeto Latin American Documentary: Vol. 1–3.; Vieira et al., 2016VIEIRA, F.G., MATSUZAKI, A.A., BARROS, B.S.F., OHARA, W.M., PAIXÃO, A.D.C., TORRENTE-VILARA, G., ZUANON, J. & DORIA, C.R.C. (2016). Catalogo de peixes da ESEC Cuniã.; Stegmann et al., 2019STEGMANN, L.F., LEITÃO, R.P., ZUANON, J. & MAGNUSSON, W.E. (2019). Distance to large rivers affects fish diversity patterns in highly dynamic streams of Central Amazonia. PloS One, 14(10), e0223880.). Of the species recorded in this study, 15 have not been assessed by the IUCN, and 63 of the remaining 68 are listed as Least Concern (LC), four as Data Deficient (DD), and one as Near Threatened species (NT) (Table 2).

Discussion

In accordance with other studies conducted in the Purus-Madeira interfluve (Barros et al., 2011BARROS, D.F., ZUANON, J., MENDONÇA, F.P., SANTO, H.M.V.E., GALUCH, A.V. & ALBERNAZ, A.L.M. (2011). The fish fauna of streams in the Madeira-Purus interfluvial region, Brazilian Amazon. Check List. 7:768–773.; Queiroz et al., 2013aQUEIROZ, L.J., TORRENTE-VILARA, G., VIEIRA, F.G., OHARA, W.M., ZUANON, J. & DORIA, C.R. (2013). Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List. 9:540–548.,bQUEIROZ, L.J., TORRENTE-VILARA, G., OHARA, W.M., PIRES, T.H.S., ZUANON, J. & DORIA, C.R.C. (2013). Peixes do Rio Madeira. São Paulo: Dialeto Latin American Documentary: Vol. 1–3.; Vieira et al., 2016VIEIRA, F.G., MATSUZAKI, A.A., BARROS, B.S.F., OHARA, W.M., PAIXÃO, A.D.C., TORRENTE-VILARA, G., ZUANON, J. & DORIA, C.R.C. (2016). Catalogo de peixes da ESEC Cuniã.; Stegmann et al., 2019STEGMANN, L.F., LEITÃO, R.P., ZUANON, J. & MAGNUSSON, W.E. (2019). Distance to large rivers affects fish diversity patterns in highly dynamic streams of Central Amazonia. PloS One, 14(10), e0223880.), there was a dominance of Characiformes, followed by the Siluriformes, Cichliformes, and Gymnotiformes. The Amazon basin hosts a remarkably diverse ichthyofauna, comprising lineages from the basin and ancient continental connections, including Osteoglossiformes, Characiformes, Siluriformes, and Dipnoi. The basin also has dozens of species derived from ancestral marine species that invaded freshwater ecosystems. Notably, more than 80% of the species are Characiformes, Siluriformes, or Gymnotiformes (Dagosta & De Pinna, 2018DAGOSTA, F.C. & DE PINNA, M.C. (2018). A history of the biogeography of Amazonian fishes. Neotropical Ichthyology, 16:e180023.; 2019DAGOSTA, F.C.P. & DE PINNA, M.C.C. (2019). The fishes of the Amazon: Distribution and biogeographical patterns, with a comprehensive list of species. Bulletin of the American Museum of Natural History, 431:1–163. https://doi.org/10.1206/0003-0090.431.1.1.
https://doi.org/10.1206/0003-0090.431.1.... ).

Apistogramma agassizii, Gladioglanis conquistador, Hemigrammus ocellifer and Nannostomus eques were widely distributed in streams in the two studied modules. These species were also captured by Barros et al. (2011)BARROS, D.F., ZUANON, J., MENDONÇA, F.P., SANTO, H.M.V.E., GALUCH, A.V. & ALBERNAZ, A.L.M. (2011). The fish fauna of streams in the Madeira-Purus interfluvial region, Brazilian Amazon. Check List. 7:768–773., Queiroz et al. (2013a)QUEIROZ, L.J., TORRENTE-VILARA, G., VIEIRA, F.G., OHARA, W.M., ZUANON, J. & DORIA, C.R. (2013). Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List. 9:540–548., Vieira et al. (2016)VIEIRA, F.G., MATSUZAKI, A.A., BARROS, B.S.F., OHARA, W.M., PAIXÃO, A.D.C., TORRENTE-VILARA, G., ZUANON, J. & DORIA, C.R.C. (2016). Catalogo de peixes da ESEC Cuniã., and Stegmann et al. (2019)STEGMANN, L.F., LEITÃO, R.P., ZUANON, J. & MAGNUSSON, W.E. (2019). Distance to large rivers affects fish diversity patterns in highly dynamic streams of Central Amazonia. PloS One, 14(10), e0223880., suggesting that they are commonly found in small streams along the Purus-Madeira interfluve. Addionally, the species identified as “cf,” “aff,” and “sp” are probably related to new species, such as Characidium sp. ‘mancha pedúnculo,’ and little-known taxonomic groups, such as Hemigrammus cf bellottii.

The elevated diversity found in this stretch of the Purus-Madeira interfluve highlights a rich ichthyofaunal diversity, also shown in other studies conducted in this region (see Barros et al., 2011BARROS, D.F., ZUANON, J., MENDONÇA, F.P., SANTO, H.M.V.E., GALUCH, A.V. & ALBERNAZ, A.L.M. (2011). The fish fauna of streams in the Madeira-Purus interfluvial region, Brazilian Amazon. Check List. 7:768–773.; Queiroz et al., 2013aQUEIROZ, L.J., TORRENTE-VILARA, G., VIEIRA, F.G., OHARA, W.M., ZUANON, J. & DORIA, C.R. (2013). Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List. 9:540–548.,bQUEIROZ, L.J., TORRENTE-VILARA, G., OHARA, W.M., PIRES, T.H.S., ZUANON, J. & DORIA, C.R.C. (2013). Peixes do Rio Madeira. São Paulo: Dialeto Latin American Documentary: Vol. 1–3.; Vieira et al., 2016VIEIRA, F.G., MATSUZAKI, A.A., BARROS, B.S.F., OHARA, W.M., PAIXÃO, A.D.C., TORRENTE-VILARA, G., ZUANON, J. & DORIA, C.R.C. (2016). Catalogo de peixes da ESEC Cuniã.; Stegmann et al., 2019STEGMANN, L.F., LEITÃO, R.P., ZUANON, J. & MAGNUSSON, W.E. (2019). Distance to large rivers affects fish diversity patterns in highly dynamic streams of Central Amazonia. PloS One, 14(10), e0223880.). The Madeira River is one of the most biodiverse Amazon-River tributaries, with over 1000 documented species (Ohara et al., 2015OHARA, W.M., DE QUEIROZ, L.J., ZUANON, J., TORRENTE-VILARA, G., VIEIRA, F.G., & DA COSTA DORIA, C.R. (2015). Fish collection of the Universidade Federal de Rondônia: its importance to the knowledge of Amazonian fish diversity. Acta Scientiarum. Biological Sciences, 37(2):251–258.). It is situated in the Amazonian lowlands, and its tributaries originate from the Andean Mountains and Brazilian Shield, which are regions that host a many endemic species (Dagosta & De Pinna, 2019DAGOSTA, F.C.P. & DE PINNA, M.C.C. (2019). The fishes of the Amazon: Distribution and biogeographical patterns, with a comprehensive list of species. Bulletin of the American Museum of Natural History, 431:1–163. https://doi.org/10.1206/0003-0090.431.1.1.
https://doi.org/10.1206/0003-0090.431.1.... ). One of the factors that may explain this elevated fish diversity in our study is the proximity of these areas to large rivers, such as the Madeira River (Stegmann et al., 2019STEGMANN, L.F., LEITÃO, R.P., ZUANON, J. & MAGNUSSON, W.E. (2019). Distance to large rivers affects fish diversity patterns in highly dynamic streams of Central Amazonia. PloS One, 14(10), e0223880.), which allows an interchange of fish species during the flood period, when the refugia are amplified (Zuanon et al., 2015ZUANON, J., MENDONÇA, F.P., ESPÍRITO-SANTO, H.M., DIAS, M.S., GALUCH, A.V. & AKAMA, A. (2015). Guia de Peixes da Reserva Ducke, Amazônia Central.INPA, Manaus, 154 pp.; Rapp Py-Daniel et al., 2017RAPP PY-DANIEL, L.H., BELTRÃO, H.D.A. & DUARTE, C. (2017). Ictiofauna do rio Jufari e aquipélago de Mariuá. In: Oliveira ML (Ed.) A flora, a fauna e o homem no maior aquipélado fluvial do planeta. Editora INPA, Manaus, 68–99. https://doi.org/10.1590/2175-7860201768117.
https://doi.org/10.1590/2175-78602017681... ). Another fact to consider is that in the study conducted by Queiroz et al. (2013b)QUEIROZ, L.J., TORRENTE-VILARA, G., OHARA, W.M., PIRES, T.H.S., ZUANON, J. & DORIA, C.R.C. (2013). Peixes do Rio Madeira. São Paulo: Dialeto Latin American Documentary: Vol. 1–3., the fish were collected from streams that connect to Lake Cuniã and this in turn, connects to the Madeira River, providing a wide variety of environments and consequently, a greater diversity of fish.

Even though studies of stream fish have advanced (Castro et al., 2021CASTRO, R.M.C. (2021). Evolução da ictiofauna de riachos sul-americanos (Castro, 1999) revisitado após mais de duas décadas. Oecologia Australis, 25(2):231–245. https://doi.org/10.4257/oeco.2021.2502.02.
https://doi.org/10.4257/oeco.2021.2502.0... ), the basic biology of the ichthyofauna in the Purus-Madeira interfluve is still largely unknown. Though 68 species are on the IUCN red list (IUCN, 2024), other authors, such as Ayla et al. (2021), only found 22 species listed in the IUCN red list of the 164 collected on the lower reaches of the Ucayalli River, Peru. This lack of information impairs assertive evaluations of conservation status, and it is related to the difficulty of access to many areas, which generates information gaps in the Amazon’s most remote regions (Carvalho et al., 2023CARVALHO, R.L., RESENDE, A.F., BARLOW, J., FRANÇA, F.M., MOURA, M.R., MACIEL, R., ... & DALY, D. (2023). Pervasive gaps in Amazonian ecological research. Current Biology.). Biological surveys are needed to provide data about species richness and distribution, guiding the path to the delimitation of priority areas for conservation and the development of public policies.

We captured less species than previous studies in the region, but Queiroz et al. (2013b)QUEIROZ, L.J., TORRENTE-VILARA, G., OHARA, W.M., PIRES, T.H.S., ZUANON, J. & DORIA, C.R.C. (2013). Peixes do Rio Madeira. São Paulo: Dialeto Latin American Documentary: Vol. 1–3. used other sampling methods in addition to those used in this study, such as seine nets, gill nets and hand nets, and collected other environments, such as lakes and their tributaries, collecting 25 samples over two years, resulting in a total of 133 species. Vieira et al. (2016)VIEIRA, F.G., MATSUZAKI, A.A., BARROS, B.S.F., OHARA, W.M., PAIXÃO, A.D.C., TORRENTE-VILARA, G., ZUANON, J. & DORIA, C.R.C. (2016). Catalogo de peixes da ESEC Cuniã., also collected over two years and used complementary methods, such as fyke nets.

Another factor that also contributes to the high diversity records is the proximity of the sampled areas to the military area of the 54th Jungle Infantry Battalion. The four sampled streams in this study are inside military areas and have restricted access, which can indirectly promote the conservation of the vegetation cover – extremally important for the maintenance of fish populations (Castello et al., 2013CASTELLO, L., MCGRATH, D.G., HESS, L.L., COE, M.T., LEFEBVRE, P.A., PETRY, P. & ARANTES, C.C. (2013). The vulnerability of Amazon freshwater ecosystems. Conservation Letters, 6(4):217–229.; Lobón-Cerviá et al., 2015LOBÓN-CERVIÁ, J., HESS, L.L., MELACK, J.M. & ARAUJO-LIMA, C.A. (2015). The importance of forest cover for fish richness and abundance on the Amazon floodplain. Hydrobiologia, 750(1):245–255.; Arantes et al., 2017ARANTES, C.C., WINEMILLER, K.O., PETRERE, M., CASTELLO, L., HESS, L.L. & FREITAS, C.E. (2017). Relationships between forest cover and fish diversity in the Amazon River floodplain. Journal of Applied Ecology, 55(1):386–395.).

The presence of the military base increases the value of these areas as potential biodiversity refugees, especially for the the streams S3 and S4 (Figure 1), which are located only a few kilometers from the military headquarters. Two results stand out regarding the surveys carried out in this study. The first concerns the 11 new species-occurrence records showing the enormous gaps in knowledge of biodiversity, and the need for better-informed public policies to guide territorial management along the Purus-Madeira interfluve. The second result is related to the many of the species collected that could not be identified at the lowest taxonomic level, which indicates the need for further taxonomic studies.

As pointed by Espírito-Santo et al. (2009), changes in the fish-assemblages composition along the year must be evaluated carefully so as not to be confused with anthropic impacts, especially when considering the inundation pulses, which can cause serious limitations for the methodology proposed by Mendonça et al. (2005)MENDONÇA, P.F., MAGNUSSON, E.W. & ZUANON, J. (2005). Relationships Between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia; Copeia 2005:751–764., and consequently, over management alternatives and conservation efforts, especially considering periods when the streams were too full to apply the method. In these regions with extreme seasonal differences in stream width and depth, complementary sampling methods (e. g., the use of stationary nets/non active assessments) are necessary to document the fish diversity.

Acknowledgments

This research was funded by the 2020-2021 Biodiversa and Water JPI joint call for research projects, under the BiodivRestore ERA-NET Cofund (GA n°101003777), with the EU and the funding organisations ANR, FCT, DFG, FUNDECT and Fundação de Amparo à Pesquisa no Estado do Amazonas-FAPEAM (through the Chamada Transnacional Conjunta BiodivRestore 2020-2021 – “Conservação e restauração de ecossistemas degradados e sua biodiversidade, incluindo o foco nos sistemas aquáticos” – Resolução N°016/2020) through the project ForestFisher; the Conselho Nacional de Desenvolvimento Científico e Tecnológico-CNPq, through the projects BACIAS (CNPq/MCTI/FNDCT n° 39/2022 call, process N° 407574/2022-0), Banzeiro da Educação (CNPq/MCTI n° 55/2022 call, process N° 407772/2022-7); and PELD-PSAM (CNPq/MCTI/CONFAP-FAPs/PELD N°21/2020 call, process N° 441366/2020-1). The authors would like to thank the: Alianza Aguas Amazónicas; the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior–CAPES; the Instituto Chico Mendes de Conservação da Biodiversidade – ICMBio; the Programa de Pós-Graduação em Ciências Ambientais – PPGCA/IEAA-UFAM; and the Programa de Pesquisa em Biodiversidade – PPBio Amazônia Ocidental of the Ministério da Ciência, Tecnologia e Inovação (MCTI). The Brazilian army permitted access to the áreas and provides long-term protection for the biodiversity in these áreas. Finally, the authors also would like to thank Willian M. Ohara for their help identifying the fish species, and the reviewers for their suggestions and improvements to the manuscript.

Data Availability

Marcelo Rodrigues dos Anjos, & Matheus Mendes Nina.(2018). Analise da Diversidade de Peixes do Módulo 13 do Núcleo Regional do PPBio em Humaítá-AM; Sul do Amazonas-AM. Programa de Pesquisa em Biodiversidade (PPBio). PPBioAmOc.253.2. https://ppbiodata.inpa.gov.br/metacatui/view/PPBioAmOc.253.3

References

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