Abstract:

The Amazon River basin hosts the most diverse freshwater ichthyofauna in the world, and yet huge areas of the basin remain unexplored. This is the case for the upper tributaries of the rio Negro, especially those draining the Colombian territory. Here we present a list of 224 species derived from the examination of specimens collected in the Mitú region (Vaupés Department, Colombia), the middle basin of the río Vaupés. Of the species identified in our study, 10 species are recorded from Colombia for the first time, and 26 species are newly recorded from the Colombian Amazon. The number of species we present here comprise almost one-third of the known species diversity of the Colombian Amazon and nearly a tenth of the total number of those known across the entirety of the Amazon basin. The most diverse orders were Characiformes (120 species) and Siluriformes (65 species), and the remaining six orders comprised less than 20% of total species. The study area comprised blackwater systems, which are considered to be nutrient-poor environments. We discuss some ecological aspects that might explain how this highly diverse ichthyofauna originates and is maintain in less productive systems. The list presented here adds an important number of new records and complements the information derived from previous studies, carried out thus far with regards to the fish fauna of the Colombian Amazon.

Keywords:
Distribution; Neotropical ichthyology; species diversity; upper rio Negro basin

Resumo:

La cuenca del río Amazonas alberga la ictiofauna dulceacuícola más diversa del mundo, sin embargo, grandes áreas de la cuenca permanecen inexploradas. Este es el caso de los afluentes de la parte alta del río Negro, especialmente los sistemas que drenan el territorio colombiano. A continuación, presentamos un listado de 224 especies derivadas del análisis de especímenes recolectados en la región de Mitú, cuenca media del río Vaupés (Departamento de Vaupés, Colombia). De las especies identificadas, 10 especies se registran en Colombia por primera vez y 26 especies para la Amazonía colombiana. El número de especies que presentamos aquí comprende casi un tercio de las especies conocidas para la Amazonía colombiana y casi una décima parte del total de las conocidas para la gran cuenca del Amazonas. Los órdenes más diversos fueron Characiformes (120 especies) y Siluriformes (65 especies), y los seis órdenes restantes comprendieron menos del 20% del total de especies. El área de estudio comprende sistemas de aguas negras que se consideran ambientes poco productivos por sus bajos contenidos de nutrientes. Discutimos aquí algunos aspectos ecológicos que podrían explicar cómo esta ictiofauna tan diversa tiene su origen y es mantenida en estos sistemas poco productivos. La información derivada del presente estudio adiciona nuevos registros de especies de peces para Colombia, y complementa la información derivada de los estudios realizados a la fecha en la Amazonía colombiana.

Palavras-chave:
Distribución de especies; diversidad de especies; cuenca alta del río Negroictiología Neotropical

Introduction

The río Vaupés is one of the main affluents of the río Negro in the Amazon Basin in Colombia (IDEAM 2004IDEAM. 2004. Guía técnico científica para la ordenación y manejo de cuencas hidrográficas en Colombia., Latrubesse & Franzinelli 2005LATRUBESSE, E.M. & FRANZINELLI, E. 2005. The late Quaternary evolution of the Negro River, Amazon, Brazil: Implications for island and floodplain formation in large anabranching tropical systems. Geomorphology 70(3-4 SPEC. ISS.):372-397.). Its headwaters are located at the Department of Guaviare in the Vega of Caquetá. An area named by Hamilton Rice (1910)HAMILTON RICE, B.A. 1910. The River Uaupés. Geogr. Journal. R. Geogr. Soc. (with Inst. Br. Geogr. 35(6):682-700., where he assumed as the commencement of the Amazon forest and where the río Guaviare and río Inírida also originate. Even though the upper reaches of the Vaupés system are located in the Vega de Caquetá, it is termed as the río Vaupés downstream of the confluence of the río Unilla and the río Itilla, at 300 MASL (IGAC 1999IGAC. 1999. Paisajes fisiográficos de Orinoquia-Amazonia (ORAM) Colombia. Análisis Geográficos. MINISTERIO DE HACIENDA Y CREDITO PUBLICO, INSTITUTO GEOGRAFICO AGUSTIN CODAZZI.), NW of the Miraflores Municipality. The río Vaupés drains from west to east, through the southeastern territory of the Guaviare department and the central region of the Vaupés Department, extending to the confluence with the río Papurí, at the border between Colombia and Brazil, where it becomes the rio Uaupés (Figure 1).

Figure 1
a) Río Vaupés/Uaupes Basin. Red square = study area. b) Study area: Mitú Region. Dots = collecting sites.

The río Vaupés forms a meandric system with high sediment load at its upper reaches. Downstream, it becomes less meandric and water properties turn out to typically Amazonian blackwaters (Hamilton Rice 1910HAMILTON RICE, B.A. 1910. The River Uaupés. Geogr. Journal. R. Geogr. Soc. (with Inst. Br. Geogr. 35(6):682-700.). Blackwater systems drain terra firme forests and savannas. Electrolyte sequestering by the root-mycorrhiza of the forest and the highly leached soils of the catchment area, account for the low turbidity and nutrient levels. Because these systems are typically free of sediment and the high contents of humic compounds, they are darkly stained (Sioli 1984aSIOLI, H. 1984a. The Amazon: Limnology and Landscape Ecology of a Mighty Tropical River and its Basin. W. Junk, Dordrecht, Boston, Hingham, MA., Leenheer 1980LEENHEER, J.A. 1980. Origin and nature of humic substances in the waters of the Amazon River basin. Acta Amaz. 10(3):513-526.).

As a typical Amazonian system, it exhibits a flood pulse, such as the adjacent forest remains flooded during high water periods - which in this case lasts up to five months of the year. This flood regime is regulated by the pluviosity conditions of the regional watershed, as well as local rainy events. The seasonal cycle consists of four well-recognized hydrological periods: high waters, low waters, and two transition periods of rising and falling waters (IGAC 1996IGAC. 1996. Calidad de aguas naturales de la cuenca media del Río Vaupés, con énfasis en las comunidades de peces. In Aspectos ambientales para el ordenamiento territorial del municipio de Mitú (departamento del Vaupés) Subdirección Agrología. Instituto Geográfico Agustín Codazzi, Bogotá, p.925-966., 1999IGAC. 1999. Paisajes fisiográficos de Orinoquia-Amazonia (ORAM) Colombia. Análisis Geográficos. MINISTERIO DE HACIENDA Y CREDITO PUBLICO, INSTITUTO GEOGRAFICO AGUSTIN CODAZZI.).

The area contains well-preserved forested areas, with 3 main floristic types: flooded forests, white-sand forests, and terra firme forests (Rudas Lleras 2009RUDAS LLERAS, A. 2009. Unidades ecogeográficas y su relación con la diversidad vegetal de la amazonia colombiana. universidad Nacional de Colombia.). Those three floristic types are found along the margin of the aquatic systems. The main river channel has a strong influence on its smaller tributaries, due to transportation of higher volumes of water, 8.200 m³/s (IGAC 1999IGAC. 1999. Paisajes fisiográficos de Orinoquia-Amazonia (ORAM) Colombia. Análisis Geográficos. MINISTERIO DE HACIENDA Y CREDITO PUBLICO, INSTITUTO GEOGRAFICO AGUSTIN CODAZZI.). Streams are characterized by a stained brown color, with sandy and rocky substrates, which may present considerable areas of beach during the low water season.

Studies have reported lower fish species richness in blackwater systems compared to nutrient rich environments (Henderson & Crampton 1997HENDERSON, P.A. & CRAMPTON, W.G.R. 1997. A comparison of fish diversity and abundance between nutrient-rich and nutrient-poor lakes in the Upper Amazon. J. Trop. Ecol. 13175-198., Bogotá-Gregory, Lima, et al. 2020BOGOTÁ-GREGORY, J.D., LIMA, F.C.T., CORREA, S.B., OLIVEIRA, C.S., JENKINS, D.G., RIBEIRO, F.R., LOVEJOY, N.R., REIS, R.E. & CRAMPTON, W.G.R. 2020. Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages. Sci. Rep. 1-15.). Nevertheless, studies have shown that they support relatively diverse ichthyofaunas composed mainly of small fishes adapted to survive in less productive habitats (Goulding et al. 1988GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing., Arbeláez, Duivenvoorden, Maldonado-Ocampo, et al. 2008ARBELÁEZ, F., DUIVENVOORDEN, J.F., MALDONADO-OCAMPO, J.A., ARBELAEZ, F., DUIVENVOORDEN, J.F. & MALDONADO-OCAMPO, J.A. 2008. Geological differentiation explains diversity and composition of fish communities in upland streams in the southern Amazon of Colombia. J. Trop. Ecol. 24(05):505-515., Arbelaez et al. 2004ARBELAEZ, F., GALVIS, G., MOJICA, J.I. & DUQUE, S. 2004. Composition and richnes of the ichthyofauna in a terra firme forest stream of the Colombian Amazonia. Amaz. Oecologia Reg. Syst. Fluminis Amaz. 18(1-2):95-107., Mojica et al. 2009MOJICA, J.I., CASTELLANOS, C. & LOBON-CERVIA, J. 2009. High temporal species turnover enhances the complexity of fish assemblages in Amazonian Terra firme streams. Ecol. Freshw. Fish 18(4):520-526., Machado-Allison et al. 2013MACHADO-ALLISON, A., MESA S., L.M. & LASSO, C.A. 2013. Peces de los morichales y canangunchales de la Orinoquia y Amazonia colombo-venezolano: una aproximación a su conocimiento, uso y conservación. In Morichales y canangunchales de la Orinoquia y Amazonia: Colombia - Venezuela. Parte I. Serie Editorial Recursos Hidrobiológicos y Pesqueros de Colombia. Instituto de Investigación de Recursos Biológicos Alexander von Humboldt (IAvH), Bogotá, D.C., Colombia, p.289-334., Antonio & Lasso 2003ANTONIO, M.E. & LASSO, C.A. 2003. Los peces del río Morichal Largo, Estados Monagas y Anzoátegui, cuenca del río Orinoco, Venezuela. Mem. Fund. La Salle Ciencias Nat. 1565-118., Machado-Allison et al. 2003MACHADO-ALLISON, A., CHERNOFF, B., PROVENZANO, F., WILLINK, P.W., MARCANO, A., PETRY, P., SIDLAUSKAS, B. & JONES, T. 2003. Inventory, Relative Abundance and Importance of Fishes in the Caura River Basin, Bolívar State, Venezuela. In A Biological Assessment of the Aquatic Ecosystems of the Caura River Basin, Bolívar State, Venezuela. RAP Bulletin of Biological Assessment 28 (B. Chernoff, A. Machado-Allison, K. Riseng, & J. R. Montambault, eds) p.64-74.). Fish community comparisons (Saint-Paul et al. 2000SAINT-PAUL, U., ZUANON, J., CORREA, M.A. V, GARCIA, M., FABRE, N.N., BERGER, U. & JUNK, W.J. 2000. Fish communities in central Amazonian white- and blackwater floodplains. Environ. Biol. Fishes 57(3):235-250.) support the notion of “rich life in poor water” as originally described by Goulding et al. (1988)GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing., which maintains that the paradoxically high fish species richness of tropical oligotrophic waters is possible because the energy sustaining fish populations is derived primarily from allochthonous forest inputs, rather than in situ autochthonous productivity. Studies of terrestrial-aquatic trophic linkages in blackwater rivers have subsequently confirmed that allochthonous inputs from flooded forests are the dominant energy source for fish in blackwater rivers (Correa & Winemiller 2018CORREA, S.B. & WINEMILLER, K. 2018. Terrestrial-aquatic trophic linkages support fish production in a tropical oligotrophic river. Oecologia 186(4):1069-1078.).

Consistent with the rich life in poor water hypothesis (Goulding et al. 1988GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing.), we report high species diversity, with a list of 224 fish species from the Mitú Region, an area in which the freshwater fish diversity was previously underestimated. Previous fish reports are mostly based on reviews that have attempted to compile available information for the río Vaupes (e.g. Mojica 1999MOJICA, J.I. 1999. Lista preliminar de las especies de peces dulceacuícolas de Colombia. Rev. la Acad. Colomb. Ciencias Exactas, Físicas y Nat. 23547-565.; Bogotá-Gregory and Maldonado-Ocampo 2006BOGOTÁ-GREGORY, D.J. & MALDONADO-OCAMPO, J.A. 2006. Peces de la zona hidrogeográfica de la Amazonia, Colombia. Biota Colomb. 14155-94.). These studies have reported fewer than 30 fish species for the whole río Vaupés basin in the Colombian territory. The relatively small number of reports from the basin only reflects the paucity of scientific research studies pertaining to fishes in the region. The most likely explanation for why more complete species inventories has yet to be undertaken in the region is due to its geographical location. Access to the area is logistically demanding for a number of reasons, and further limited for social reasons, given that a history of armed conflict has hampered biological surveys in general. Nevertheless, because of recent improvements in the social context of the region, it is now relatively accessible for biological surveys, and more complete species inventories in the region can be carried out.

Despite the recognition of the Amazon River basin as the region with the highest freshwater fish diversity, there are huge areas that remain unexplored. One such area is the hydrographic network that drains the soils of the Mitú Region, an Amazonian system that was previously poorly explored and may be characterized by specialized ichthyofaunas. Our results are part of an inter-institutional initiative of the Instituto Amazónico de Investigaciones Científicas-SINCHI, the environmental corporation CDA, the Universidad del Tolima-UT, and WWF-Colombia, with the intention to fill major gaps in our knowledge of remote areas of the Amazon Basin. The aim of this initiative is to contribute to national species inventory (DoNascimiento et al. 2017DONASCIMIENTO, C., HERRERA, E.E., HERRERA, G., ORTEGA-LARA, A., VILLA-NAVARRO, F., USMA, J.S. & MALDONADO-OCAMPO, J.A. 2017. Checklist of the freshwater fishes of Colombia: a DwC alternative to the updating problem. Press 13825-138., Maldonado-Ocampo et al. 2008MALDONADO-OCAMPO, J.A., RICHARD, P. & USMA, J.S. 2008. Checklist of the Freshwater Fishes of Colombia. Biota Colomb. 9q(2):143-237.) and strengthen the scientific reference collections with the aid of local communities.

Materials and Methods

The study area is located near to the Mitú municipality, department of Vaupés, Colombia, along the main channel of the río Vaupés, río Papuri, río Cuduyari, río Paca, and the Mituceño, and Yi streams (Figure 1). The area is a typical equatorial zone, where daily temperature range between and 18 - 34˚C. The area presents a unimodal precipitation regime, that is to say, the highest precipitation values are registered between June and July, followed by a transition period where rainfall decrease in August and September, and the period with the lowest precipitation values falls between December and March (IGAC 1996IGAC. 1996. Calidad de aguas naturales de la cuenca media del Río Vaupés, con énfasis en las comunidades de peces. In Aspectos ambientales para el ordenamiento territorial del municipio de Mitú (departamento del Vaupés) Subdirección Agrología. Instituto Geográfico Agustín Codazzi, Bogotá, p.925-966.).

To document species composition in the study area and not for comparative purposes, a series of sampling events were conducted between 2012 and 2019, during both dry and rainy seasons. Fishes were collected with conventional fishing gear (i.e. gill-nets, beach seines, and dipnets). Once fishes were captured, they were euthanized with 600 mg L^-1 eugenol, fixed with 10% formaldehyde solution and later preserved in 70% ethanol solution. Specimen vouchers are deposited in the ichthyological collections of the Universidad del Tolima (CZUT-IC) and SINCHI institute (CIACOL). The taxonomic list herein, follows the classification adopted in Fricke et al. (2020)FRICKE, R., ESCHMEYER, W.N. & LAAN VAN DER, R. 2020. Eschmeyer’s catalog of fishes: genera, species, references. Calif. Acad. Sci. for orders and families and genera and species are listed alphabetically. Validity of the species identified were confirmed also with Fricke et al. (2020)FRICKE, R., ESCHMEYER, W.N. & LAAN VAN DER, R. 2020. Eschmeyer’s catalog of fishes: genera, species, references. Calif. Acad. Sci.. Usma et al. (2009)USMA, J.S., VALDERRAMA, M., ESCOBAR, M., AJIACO-MARTÍNEZ, R.E., VILLA-NAVARRO, F., CASTRO, F., RAMÍREZ-GIL, H., SANABRIA, A.I., ORTEGA-LARA, A., MALDONADO-OCAMPO, J., ALONSO, J.C. & CIPAMOCHA, C. 2009. Peces dulceacuícolas migratorios en Colombia. In Plan Nacional de las Especies Migratorias. Diagnóstico e identificación de acciones para la conservación y manejo sostenible de las especies migratorias de la biodiversidad de Colombia (L. G. Naranjo & J. D. Amaya Espinel, eds) Dirección de Ecosistemas, Ministerio de Ambiente, Vivienda y Desarrollo Teritorial, WWF Colombia, Bogotá, D.C., p.214. was used to determine species that present relatively long-distance migratory longitudinal movements.

Acronyms of fish collection where specimens are deposited are provided for future revisions. Data from CIACOL will be available at the Catalogue of Species of the Colombia Biodiversity Information System (http://www.biodiversidad.co/) Currently, CIACOL data is hosted in the online collection’s catalogue (https://sinchi.org.co/ciacol) and those of CZUT-IC are available at: https://doi.org/10.15472/bhprvq

We classified species based on standard length (SL) into four size classes; miniature species, less than 2.6 cm of SL; small species, over 2.6 and less than 15 cm of SL; medium species, between 15 and 45; and large species, with over 45 cm of SL. This simple scheme for size classification is a unification of Weitzman and Vari (1988)WEITZMAN, S. & VARI, R. 1988. Miniaturization in South American freshwater fishes: an overview and discussion. Proc. Biol. Soc. Washingt. 101(2):444-465., Castro (1999)CASTRO, R.M.C. 1999. Evolução da ictiofauna de riachos sul-americanos: padrões gerais e possíveis processos causais. Oecologia Aust. 06(01):139-155., and Castro et al. (2005)CASTRO, R.M.C., CASATTI, L., SANTOS, H.E., VARI, R.P., MELO, A.L.A., MARTINS, L.S.E., ABREU, T.X., BENINE, R.C., GIBRAN, F.Z., RIBEIRO, A.C., BOCKMANN, F.A., CARVALHO, M., PELICAO, G.Z.P., FERREIRA, K.M., STOPIGLIA, R. & AKAMA, A. 2005. Structure and composition of the stream ichthyofauna of four tributary rivers of the upper Rio Parana basin, Brazil. Ichthyol. Explor. Freshwaters 16(3):193-214., which allowed us to calculate percentage of miniature and small body species that represent the overall species composition in our study area. Body sizes were obtained with Reis et al. (2003)REIS, R.E., KULLANDER, S.O. & FERRARIS, C.J. 2003. Checklist of the Freshwater Fishes of South and Central America. Edipucrs, Porto Alegre, Brazil., original species descriptions, and direct measurements in the case of undetermined species. To calculate the proportion of species exclusive to blackwaters we defined species affiliations to water type (i.e. whitewater, clearwater, and blackwater) sensu Sioli (1984b)SIOLI, H. 1984b. The Amazon: Limnology and Landscape Ecology of a Mighty Tropical River and its Basin. W. Junk, Dordrecht, Boston, Hingham, MA.. Designation of the species to a given water type was based on empirical evidence.

Results

A total of 224 species belonging to eight taxonomic orders, 37 families, and 123 genera (Table 1) were recognized for the Mitú Region. The orders with most families, genera, and species were Characiformes (17 families, 52 genera, and 120 species) and Siluriformes (10 families, 46 genera, and 65 species) (Figure 2a). The remaining five orders account less than 20% of the total genera and species identified. At the family level, Characidae and Cichlidae were the richest families, with 45 and 13 species, respectively (Figure 2b).

Figure 2
(a) Percentage of species by order and (b) number of species per family.

Of the species reported here (Table 1), 10 are new records for Colombia and 26 constitute new records for the Colombian Amazon River basin (DoNascimiento et al. 2017DONASCIMIENTO, C., HERRERA, E.E., HERRERA, G., ORTEGA-LARA, A., VILLA-NAVARRO, F., USMA, J.S. & MALDONADO-OCAMPO, J.A. 2017. Checklist of the freshwater fishes of Colombia: a DwC alternative to the updating problem. Press 13825-138.). Most of the species that are recorded for the Colombian Amazon for the first time (over the 10 % of total species reported herein), were previously recorded for other sections of the rio Negro in Brazil. None of the listed species are categorized as threatened (Mojica et al. 2012MOJICA, J.I., USMA, J.S., ÁLVAREZ-LEÓN, R. & LASSO, C.A. 2012. Libro rojo de peces dulceacuícolas de Colombia. Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, Instituto de Ciencias Naturales de la Universidad Nacional de Colombia, WWF Co- lombia y Universidad de Manizales, Bogotá, D.C.) or considered exotic or invasive (see natural distributions in Reis et al. 2003REIS, R.E., KULLANDER, S.O. & FERRARIS, C.J. 2003. Checklist of the Freshwater Fishes of South and Central America. Edipucrs, Porto Alegre, Brazil. and Fricke et al. 2020FRICKE, R., ESCHMEYER, W.N. & LAAN VAN DER, R. 2020. Eschmeyer’s catalog of fishes: genera, species, references. Calif. Acad. Sci.). 15 of the species are classified as migratory (Usma et al. 2009USMA, J.S., VALDERRAMA, M., ESCOBAR, M., AJIACO-MARTÍNEZ, R.E., VILLA-NAVARRO, F., CASTRO, F., RAMÍREZ-GIL, H., SANABRIA, A.I., ORTEGA-LARA, A., MALDONADO-OCAMPO, J., ALONSO, J.C. & CIPAMOCHA, C. 2009. Peces dulceacuícolas migratorios en Colombia. In Plan Nacional de las Especies Migratorias. Diagnóstico e identificación de acciones para la conservación y manejo sostenible de las especies migratorias de la biodiversidad de Colombia (L. G. Naranjo & J. D. Amaya Espinel, eds) Dirección de Ecosistemas, Ministerio de Ambiente, Vivienda y Desarrollo Teritorial, WWF Colombia, Bogotá, D.C., p.214.).We included in the list six undetermined species of Odonthocharacidium, Tetragonopterus, Tyttocharax, Ituglanis, Myoglanis, Nemuroglanis, and Aequidens. Unequivocal identification for these species could not be reached and further studies are required to review their specific identities. Moreover, we anticipate that some of these species may eventually be recognized as undescribed.

The percentage of species unique to blackwater systems greatly exceed those that are present in two types of water of the ones present in all three blackwater, clearwater, and whitewater systems (Figure 3a). According to the criterion defined herein for designation of size classes, the proportion of miniature and small body size species greatly exceeded that of medium and large size species (Figure 3b).

Figure 3
(a) number of species per water type: BW = blackwater, CW = clearwater, and WW = whitewater and (b) Percentage of species per size-class

Discussion

Overall, the species composition found in the middle basin of the río Vaupés (Mitú region), with taxonomic dominance of Characiformes and Siluriformes, agrees with the general pattern documented for the ichthyofaunas of the basin in the Brazilian territory (Beltrão et al. 2019BELTRÃO, H., ZUANON, J. & FERREIRA, E. 2019. Checklist of the ichthyofauna of the Rio Negro basin in the Brazilian Amazon. Zookeys 2019(881):53-89.) and other basins of the Neotropical Region (Maldonado-ocampo et al. 2006MALDONADO-OCAMPO, J.A., LUGO, M., BOGOTÁ-GREGORY, J.D., LASSO, C.A., VÁSQUEZ, L., USMA, J.S., TAPHORN, D.C. & RIZZI, P. 2006. Peces del río Tomo, cuenca del Orinoco, Colombia. Biota Colomb. 7(1):113-127., Ortega et al. 2006ORTEGA, H., MOJICA, J.I., ALONSO, J.C. & HIDALGO, M. 2006. Listado de los peces de la cuenca del río Putumayo en su sector colombo-peruano. Biota Colomb. 7(1):95-111., Ortega-lara et al. 2012ORTEGA-LARA, A., LASSO-ALCALÁ, O.M., LASSO, C.A., DE, G.A. & BOGOTÁ-GREGORY, J.D. 2012. Peces de la cuenca del río Catatumbo, cuenca del Lago de Maracaibo, Colombia y Venezuela. Biota Colomb. 13(1):71-98., Bogotá-Gregory, Lima, et al. 2020BOGOTÁ-GREGORY, J.D., LIMA, F.C.T., CORREA, S.B., OLIVEIRA, C.S., JENKINS, D.G., RIBEIRO, F.R., LOVEJOY, N.R., REIS, R.E. & CRAMPTON, W.G.R. 2020. Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages. Sci. Rep. 1-15.).

The list presented here adds 26 new species records for the Colombian Amazon. Among the new records, Melanocharacidium dispilomma Buckup 1993 was indeed reported in Bogotá-Gregory & Maldonado-Ocampo (2006)BOGOTÁ-GREGORY, D.J. & MALDONADO-OCAMPO, J.A. 2006. Peces de la zona hidrogeográfica de la Amazonia, Colombia. Biota Colomb. 14155-94.. Nevertheless, this report was based on specimens collected in Brazil, near the border of Colombia [Buckup, 1993: MNRJ 5934, río Tiquié (trib. of río Vaupés)]. Therefore, this record was dismissed in DoNascimiento et al. (2017)DONASCIMIENTO, C., HERRERA, E.E., HERRERA, G., ORTEGA-LARA, A., VILLA-NAVARRO, F., USMA, J.S. & MALDONADO-OCAMPO, J.A. 2017. Checklist of the freshwater fishes of Colombia: a DwC alternative to the updating problem. Press 13825-138. by not coming from the Colombian Amazon. The specimens referenced herein are actually the first record of the species in Colombian territory. Copella compta (Myers 1927) was included in Galvis et al. (2007)GALVIS, G., SÁNCHEZ-DUARTE, P., MESA-SALAZAR, L., LÓPEZ-PINTO, Y., GUTIÉRREZ, M., GUTIÉRREZ-CORTÉS, A., LEIVA, M. & CASTELLANOS, C. 2007. Peces de la Amazonia colombiana con enfasis en especies de interés ornamental. 489.. Nevertheless, the specimens referenced in that paper are misidentifications and belong to a species with a more conspicuous lateral band [see comments and details on diagnostic characters in Zarske & Géry (2006)].

In one of the first efforts to document the freshwater fishes from Colombia (Mojica 1999MOJICA, J.I. 1999. Lista preliminar de las especies de peces dulceacuícolas de Colombia. Rev. la Acad. Colomb. Ciencias Exactas, Físicas y Nat. 23547-565.), only four species were listed across the entirety of the río Vaupés basin: Hoplerythrinus unitaeniatus, Acanthodoras cataphractus, Platydoras hancockii, and Synbranchus marmoratus. We confirmed the presence of these species, except Platydoras hancockii, which is the only species of the genus reported for the río Negro basin (Piorski et al. 2008PIORSKI, N.M., GARAVELLO, J.C., ARCE, M. & PEREZ, M.H.S. 2008. Platydoras brachylecis, a new species of thorny catfish (Siluriformes: Doradidae) from northeastern Brazil. Neotrop. Ichthyol. 6(3):481-494.). Because of this, its presence in the río Vaupés is expected to be documented when more sampling efforts can be conducted in the area. Bogotá-Gregory and Maldonado-Ocampo (2006)BOGOTÁ-GREGORY, D.J. & MALDONADO-OCAMPO, J.A. 2006. Peces de la zona hidrogeográfica de la Amazonia, Colombia. Biota Colomb. 14155-94. increased species number in the río Vaupés to 24 species, from which 14 were here recorded (see Table S1 for species not identified in our study, but which were previously reported). Galvis et al. (2007)GALVIS, G., SÁNCHEZ-DUARTE, P., MESA-SALAZAR, L., LÓPEZ-PINTO, Y., GUTIÉRREZ, M., GUTIÉRREZ-CORTÉS, A., LEIVA, M. & CASTELLANOS, C. 2007. Peces de la Amazonia colombiana con enfasis en especies de interés ornamental. 489. in his study focused on fish species used in ornamental trade, also reported additional species for the río Vaupés basin. Lima and collaborators (2020)LIMA, F.C.T., URBANO-BONILLA, A. & PRADA-PEDREROS, S. 2020. A new Hemigrammus from the upper Río Vaupés, Colombia (Characiformes: Characidae), with a discussion on the presence of an enlarged urogenital papilla in the family. J. Fish Biol. 96868-876. described Hemigrammus xaveriellus, from the río Itilla, at the headwaters of the río Vaupés basin. More recently, Bogotá-Gregory et al. (2020BOGOTÁ-GREGORY, J.D., C. T. LIMA, F., DONASCIMIENTO, C., ACOSTA-SANTOS, A., NAVARRO-VILLA, F.A. & AGUDELO CÓRDOBA, E. 2020. First records of freshwater fish species in Colombia: extending the distribution of 17 Amazonian and Orinoco fish species. Check List 16(5):1395-1406.a) reported eight species in the Mitú Region that were not previously registered from Colombia and are included here. As can be verified from this brief account, studies regarding fish composition of the río Vaupés basin are scant. Additionally, the low species richness previously reported (Bogotá-Gregory & Maldonado-Ocampo 2006BOGOTÁ-GREGORY, D.J. & MALDONADO-OCAMPO, J.A. 2006. Peces de la zona hidrogeográfica de la Amazonia, Colombia. Biota Colomb. 14155-94.) was mainly the result of isolated sampling events, rather than the actual figure derived from extensive collection efforts in the implied region, as demonstrated in this work. The previous studies in the area are not exclusively based on specimens available in ichthyological collections, but also in literature records. This type of taxonomic lists may contain discrepancies in species identification, which are difficult to assess due to unavailability of reference specimens of the bibliographic records. Discrepancies can also arise from outdated taxonomic identifications. In our study, we counted with the collaboration of specialists in different taxonomic groups that ensures reliable taxonomic identifications.

A recent checklist for the entire portion of the rio Negro basin in Brazil, reported 1,165 species (Beltrão et al. 2019BELTRÃO, H., ZUANON, J. & FERREIRA, E. 2019. Checklist of the ichthyofauna of the Rio Negro basin in the Brazilian Amazon. Zookeys 2019(881):53-89.). However, there is little published information concerning the ichthyofauna from its upper section, above São Gabriel da Cachoeira, and particularly from the rio Uaupés basin. Lima et al. (2005)LIMA, F.C.T., RAMOS, L., BARRETO, T., CABALZAR, A., TENÓRIO, G., BARBOSA, A., TENÓRIO, F., RESENDE, A.S. & LOPES, M. 2005. Peixes do alto Tiquié: ictiologia e conhecimentos dos tuyuka e tukano. In Peixe e gente no alto rio Tiquié: conhecimentos tukano/tuyuka, ictiologia/etnologia Instituto Socioambiental, São Paulo, p.111-282. reviewed the available information for the area published at that time. The same authors presented a list for the species found in the upper portion of the rio Tiquié, an important tributary of the rio Uaupés, with headwaters within the Departamento of Vaupés, and reported 147 species for the area. Subsequent collecting in the middle portion of the rio Tiquié raised the number of species to 265 (F.C.T. Lima, unpubl. data). Several species were described in the last years, based on this fish survey (Lima & Sousa 2009LIMA, F.C.T. & SOUSA, L.M. 2009. A new species of Hemigrammus from the upper rio Negro basin, Brazil, with comments on the presence and arrangement of anal-fin hooks in Hemigrammus and related genera (Ostariophysi: Characiformes: Characidae). aqua 15(3):3-20., Marinho & Lima 2009MARINHO, M.M.F. & LIMA, F.C.T. 2009. Astyanax ajuricaba: a new species from the Amazon basin in Brazil (Characiformes: Characidae). Neotrop. Ichthyol. 7(2):169-174., Carvalho et al. 2010CARVALHO, P.H., LIMA, F.C.T. & ZAWADZKI, C.H. 2010. Two new species of the Hypostomus cochliodon group (Siluriformes: Loricariidae) from the rio Negro basin in Brazil. Neotrop. Ichthyol. 8(1):39-48., Maxime et al. 2011MAXIME, E.L., LIMA, F.C.T. & ALBERT, J.S. 2011. A new species of gymnotus (Gymnotiformes: Gymnotidae) from Rio Tiquié in Northern Brazil. Copeia 2011(1):77-81., Birindelli et al. 2012BIRINDELLI, J.L.O., LIMA, F.C.T. & BRITSKI, H.A. 2012. New species of Pseudanos Winterbottom, 1980 (Characiformes: Anostomidae), with notes on the taxonomy of P. gracilis and P. trimaculatus. Zootaxa 68(3425):55-68., Lima & Sazima 2017LIMA, F.C.T. & SAZIMA, I. 2017. Corydoras desana, a new plated catfish from the upper rio Negro, Brazil, with comments on mimicry within Corydoradinae (Ostariophysi: Siluriformes: Callichthyidae). aqua, Int. J. Ichthyol. 23(1):19-32., Pablo Lehmann et al. 2018PABLO LEHMANN, A., LIMA, F.C.T. & REIS, R.E. 2018. Parotocinclus yaka, a new species of armored catfish (Loricariidae: Hypoptopomatinae), from the Amazon basin in Brazil. Zootaxa 4521(4):584-592., Soares et al. 2019SOARES, I.M., LIMA, F.C.T. & RAPP PY-DANIEL, L.H. 2019. A New Species of Moenkhausia Eigenmann, 1903 (Characiformes, Characidae) from the Upper Rio Negro Basin, Brazil. Copeia 107(2):232-238.). However, other portions of the rio Uaupés basin in Brazil remain virtually unknown ichthyologically.

Despite recent efforts documenting fish migrations in Colombia (e.g. Usma et al. 2009USMA, J.S., VALDERRAMA, M., ESCOBAR, M., AJIACO-MARTÍNEZ, R.E., VILLA-NAVARRO, F., CASTRO, F., RAMÍREZ-GIL, H., SANABRIA, A.I., ORTEGA-LARA, A., MALDONADO-OCAMPO, J., ALONSO, J.C. & CIPAMOCHA, C. 2009. Peces dulceacuícolas migratorios en Colombia. In Plan Nacional de las Especies Migratorias. Diagnóstico e identificación de acciones para la conservación y manejo sostenible de las especies migratorias de la biodiversidad de Colombia (L. G. Naranjo & J. D. Amaya Espinel, eds) Dirección de Ecosistemas, Ministerio de Ambiente, Vivienda y Desarrollo Teritorial, WWF Colombia, Bogotá, D.C., p.214.), the río Vaupés and more generally, the Amazon basin are still incompletely studied, and movement patterns of fishes remain poorly documented. Therefore, species listed as migratory here might not be the only ones that perform large longitudinal migrations in the basin. Upstream migrations of some Leporinus species were reported by Lima et al. (2005)LIMA, F.C.T., RAMOS, L., BARRETO, T., CABALZAR, A., TENÓRIO, G., BARBOSA, A., TENÓRIO, F., RESENDE, A.S. & LOPES, M. 2005. Peixes do alto Tiquié: ictiologia e conhecimentos dos tuyuka e tukano. In Peixe e gente no alto rio Tiquié: conhecimentos tukano/tuyuka, ictiologia/etnologia Instituto Socioambiental, São Paulo, p.111-282. from the rio Tiquié.

Blackwaters have extremely low pH values, due to high content of acidic humic compounds, largely derived from incompletely decomposed organic matter, which gives the water its typical tea stained coloration (Goulding et al. 1988GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing., Leenheer 1980LEENHEER, J.A. 1980. Origin and nature of humic substances in the waters of the Amazon River basin. Acta Amaz. 10(3):513-526.). The extremely low pH exerts physiological constraints on the biota, which affects ionic balance and osmoregulation in freshwater fishes (McDonald 1982MCDONALD, D.G. 1982. The effects of H+ upon the gills fo freshwater fish. Can. J. Zool. 61(4):691-703., Wilson et al. 1999WILSON, R.W., WOOD, C.M., GONZALEZ, R.J., PATRICK, M.L., BERGMAN, H.L., NARAHARA, A. & VAL, A.L. 1999. Ion and acid-base balance in three species of Amazonian fish during gradual acidification of extremely soft water. Physiol. Biochem. Zool. (72):277-285., Matsuo & Val 2002MATSUO, A.Y. & VAL, A.L. 2002. Low pH and calcium effects on net Na+ and K+ fluxes in two catfish species from the Amazon River (Corydoras: Callichthyidae). Brazilian J. Med. Biol. Res. (35):361-367.). Physiological studies have provided experimental support for mechanisms to prevent acidification in some fish species of these kind of environments (Hirata et al. 2003HIRATA, T., KANEKO, T., ONO, T., NAKAZATO, T., FURUKAWA, N., HASEGAWA, S., WAKABAYASHI, S., SHIGEKAWA, M., CHANG, M.H., ROMERO, M.F. & HIROSE, S. 2003. Mechanism of acid adaptation of a fish living in a ph 3.5 lake. Am. J. Physiol. - Regul. Integr. Comp. Physiol. 284(5 53-5):.). Thus, the fish communities that characterizes the blackwater systems, like those we sampled in our study area, are most likely represented by species especially adapted to extreme pH conditions (Val & de Almeida 1995VAL, A.L. & DE ALMEIDA, V.M.F. 1995. Fishes of the Amazon and their Environment: Physiological and Biochemical Aspect. Springer-Verlag, Berlin.). As we evidenced in our study, more than 50% of the species identified are unique to these low pH aquatic systems.

Blackwater systems are also known for their low productivity in terms of biomass (Goulding et al. 1988GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing., Bogotá-Gregory, Lima, et al. 2020BOGOTÁ-GREGORY, J.D., LIMA, F.C.T., CORREA, S.B., OLIVEIRA, C.S., JENKINS, D.G., RIBEIRO, F.R., LOVEJOY, N.R., REIS, R.E. & CRAMPTON, W.G.R. 2020. Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages. Sci. Rep. 1-15.). This is partially reflected in the small number of blackwater-endemic fishes, only 16 species, collected commercially for human consumption (Lasso et al. 2011LASSO, C.A., AGUDELO CÓRDOBA, E., JIMÉNEZ-SEGURA, L.F., RAMÍREZ-GIL, H., MORALES-BETANCOURT, M., AJIACO-MARTÍNEZ, R.E., PAULA GUTIÉRREZ, F. de P., USMA OVIEDO, J.S., TORRES, M. & SANABRIA OCHOA, A.I. 2011. Catálogo de los recursos pesqueros continentales de Colombia. Serie Editorial Recursos Hidrobiológicos y Pesqueros Continentales de Colombia. Instituto de Investigación de Recursos Biológicos Alexander von Humboldt (IAvH), Bogotá, D.C.). In contrast, 85 species have commercial importance in the ornamental trade in Colombia (Galvis et al. 2007GALVIS, G., SÁNCHEZ-DUARTE, P., MESA-SALAZAR, L., LÓPEZ-PINTO, Y., GUTIÉRREZ, M., GUTIÉRREZ-CORTÉS, A., LEIVA, M. & CASTELLANOS, C. 2007. Peces de la Amazonia colombiana con enfasis en especies de interés ornamental. 489., AUNAP 2016AUNAP. 2016. Guía visual de los principales peces ornamentales continentales de Colombia., Nogueira et al. 2012NOGUEIRA, L.B., AZEVEDO, P.G., CANELHAS, M.R., BEDORE, A.G., LOPES, J.M. & GODINHO, H.P. 2012. Induced spawning and early ontogeny in hatchery-reared catfish Zungaro jahu (Siluriformes: Pimelodidae). Neotrop. Ichthyol. 10(1):89-98., Landines et al. 2005LANDINES, M., URUEÑA, F. & RODRIGUEZ, L. 2005. Peces Ornamentales.) (Table 1). The majority of the species in this study have small body size, which agrees with similar findings in other recent studies that have shown that the relatively nutrient-poor systems can indeed maintain a relatively diverse ichthyofauna, yet mainly composed of small fishes that had acquired proper adaptations to thrive in less productive habitats (Arbeláez, Duivenvoorden & Maldonado-Ocampo 2008ARBELÁEZ, F., DUIVENVOORDEN, J.F. & MALDONADO-OCAMPO, J.A. 2008. Geological differentiation explains diversity and composition of fish communities in upland streams in the southern Amazon of Colombia. J. Trop. Ecol. 24(05):505-515., Arbelaez et al. 2004ARBELAEZ, F., GALVIS, G., MOJICA, J.I. & DUQUE, S. 2004. Composition and richnes of the ichthyofauna in a terra firme forest stream of the Colombian Amazonia. Amaz. Oecologia Reg. Syst. Fluminis Amaz. 18(1-2):95-107., Mojica et al. 2009MOJICA, J.I., CASTELLANOS, C. & LOBON-CERVIA, J. 2009. High temporal species turnover enhances the complexity of fish assemblages in Amazonian Terra firme streams. Ecol. Freshw. Fish 18(4):520-526., Goulding et al. 1988GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing., Machado-Allison et al. 2013MACHADO-ALLISON, A., MESA S., L.M. & LASSO, C.A. 2013. Peces de los morichales y canangunchales de la Orinoquia y Amazonia colombo-venezolano: una aproximación a su conocimiento, uso y conservación. In Morichales y canangunchales de la Orinoquia y Amazonia: Colombia - Venezuela. Parte I. Serie Editorial Recursos Hidrobiológicos y Pesqueros de Colombia. Instituto de Investigación de Recursos Biológicos Alexander von Humboldt (IAvH), Bogotá, D.C., Colombia, p.289-334., 2003MACHADO-ALLISON, A., CHERNOFF, B., PROVENZANO, F., WILLINK, P.W., MARCANO, A., PETRY, P., SIDLAUSKAS, B. & JONES, T. 2003. Inventory, Relative Abundance and Importance of Fishes in the Caura River Basin, Bolívar State, Venezuela. In A Biological Assessment of the Aquatic Ecosystems of the Caura River Basin, Bolívar State, Venezuela. RAP Bulletin of Biological Assessment 28 (B. Chernoff, A. Machado-Allison, K. Riseng, & J. R. Montambault, eds) p.64-74., Lasso et al. 2006LASSO, C.A., SEÑARÌS, J.C., ALONSO, L.E. & FLORES, A. 2006. Evaluación Rápida de la Biodiversidad de los Ecosistemas Acuáticos en la Confluencia de los ríos Orinoco y Ventuari, Estado Amazonas (Venezuela). Boletín RAP de Evaluación Biológica 30. Conservación Internacional, Washington, DC, USA.). On the contrary, the majority of medium to large size species are associated with large longitudinal migratory movements (Castro & Polaz 2020CASTRO, R.M.C. & POLAZ, C.N.M. 2020. Small-sized fish: the largest and most threatened portion of the megadiverse neotropical freshwater fish fauna. Biota Neotrop. 20(1):1-12.). And because of this they’re mostly found in the main channels of more productive systems where they found better conditions as nursery areas (De Lima & Araujo-Lima 2004DE LIMA, Á.C. & ARAUJO-LIMA, C.A.R.M. 2004. The distributions of larval and juvenile fishes in Amazonian rivers of different nutrient status. Freshw. Biol. 49(6):787-800.).

In less productive systems, like the blackwater rivers of the Amazon basin, most of the energy obtained by the aquatic fauna is of allochthonous origin. The adjacent forests provide food resources in the form of fruits, seeds, and arthropods (Goulding et al. 1988GOULDING, M., CARVALHO, M.L. & FERREIRA, E.G. 1988. Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Trough Fish Communities. The Hague: SPB Academic Publishing., Lowe-McConnell 1987LOWE-MCCONNELL, R.H. 1987. Ecological studies in tropical fish communities. Cambridges University Press, New York.). One of the strategies by which these highly diverse communities can be maintained could be by reducing their biomass. In this manner, blackwater systems can maintain highly diverse fish communities with relatively low abundances, as shown by Saint-Paul et al. (2000)SAINT-PAUL, U., ZUANON, J., CORREA, M.A. V, GARCIA, M., FABRE, N.N., BERGER, U. & JUNK, W.J. 2000. Fish communities in central Amazonian white- and blackwater floodplains. Environ. Biol. Fishes 57(3):235-250., in a comparison between blackwater and whitewater floodplain fish communities. Another of the most important adaptations observed thus far is miniaturization, which includes paedomorphic retention of juvenile characteristics and reductive morphological evolution. Miniaturization has evolved on multiple occasions in Neotropical fishes, as a way to occupy interstitial habitats of marginal vegetation and leaf litter of the substrate (Crampton 2011CRAMPTON, W.G.R. 2011. An ecological perspective on diversity and distributions. In Historical Biogeography of Neotropical Freshwater Fishes (J. S. Albert & R. E. Reis, eds) University of California Press, Berkeley., Weitzman & Vari 1988WEITZMAN, S. & VARI, R. 1988. Miniaturization in South American freshwater fishes: an overview and discussion. Proc. Biol. Soc. Washingt. 101(2):444-465.).

The new records presented here for the Colombian Amazon reflects scarcity in the studies carried out thus far with regards to the fish fauna of the region. While most ichthyological surveys have been performed in the surroundings of populated localities, with emphasis on species of commercial importance (Bogotá-Gregory & Maldonado-Ocampo 2006BOGOTÁ-GREGORY, D.J. & MALDONADO-OCAMPO, J.A. 2006. Peces de la zona hidrogeográfica de la Amazonia, Colombia. Biota Colomb. 14155-94.), this study was carried out to survey previously little-explored areas. Over the last four decades, intensive field collections and improvements in taxonomy have yielded an improved understanding of how Amazonian fish species are distributed among the Amazon’s aquatic ecosystems. However, there are still huge remote areas that remain unexplored, and we are not yet close to knowing the species diversity of these pristine areas.

Initiatives that encompass studies like ours, allow us to document the ichthyofauna of the most diverse region in the world. The information and analyses generated by this study will be of utility to a broad range of researchers interested - including from the fields of ecology, biogeography, and taxonomy. Aditionally, it constitute important baselines for its application in management and conservation plans. This is important in light of the habitat degradation that freshwater fish species are facing due to anthropogenic activities. Deforestation, mining, dam-construction, and overfishing threaten most of the Amazon region, and management and conservation plans are still lacking (Abell et al. 2008ABELL, R. et al. 2008. Freshwater ecoregions of the world: A new map of biogeographic units for freshwater biodiversity conservation. Bioscience 58(5):403-414.).

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Acknowledgements

This study was funded by the Grupo de Investigación en Ecosistemas Acuáticos Amazónicos of the SINCHI Institute, CDA, Asocriva (the Vaupés Indigenous Asociation), and WWF-Colombia. Jesús Dámaso and Marcela Núñez for their support during the fieldwork. Members of the headquarters of the SINCHI Institute at Mitú, Vaupés, especially to Luis Fernando Jaramillo. Joseph Waddell for English revision. This study is dedicated to Dairon Cárdenas López, dearest colleague and friend, coordinator of the Sinchi’s Ecosystems and Natural Resources Program.

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