Introduction

The Orinoco River Basin, with an area of 981,446 km2, shared between Venezuela (65 %) and Colombia (35 %) (Lasso et al. 2016), harbors 1002 fish species (Reis et al. 2016), from which more than 66 % (663 spp.) are found in Colombia (DoNascimiento et al. 2017), in different aquatic systems of the Andean Orinoco, piedmont and savannahs natural ecoregions (Abell et al. 2008).

The tributaries of the Orinoco River in Colombia are the Arauca, Guaviare, Vichada, Inírida, Tomo, Bita and Meta rivers, where the sampling effort and the level of knowledge are low (scores 1 or 2 on a scale of 1 to 4) and the information gap is high (scores 3 and 4 on a scale of 1 to 4) (Lasso et al. 2016). The Meta River is the main Colombian Orinoco tributary with an area of 10830,4 km2 (Machado-Allison et al. 2010), medium to high fish species richness and important levels of endemism (of 577 species recorded, 10 or more are endemics), and high importance for local human communities with 298 economically important species (Usma et al. 2016). However, part of this richness is currently threatened with 15 species classified as Endangered (Mojica et al. 2012), mainly as an effect of several anthropic impacts such as land conversion and habitat loss, especially in the piedmont and savannah regions (Barletta et al. 2010, 2016, Reis et al. 2016).

In the last few years, the increase in the ichthyological knowledge has been significant for the principal tributaries of the Meta River (Mojica 1999, Urbano- Bonilla et al. 2009, 2014, Villa-Navarro et al. 2011, Maldonado-Ocampo et al. 2013, Usma et al. 2016). However, there are still poorly-known drainages such as the Casanare River drainage, that currently has information gaps (Machado-Allison et al. 2010, Lasso et al. 2016), and for which only 20 fish species have been recorded (Villa-Navarro et al. 2011). For this reason, the ichthyological inventory of the piedmont and savannahs of the Casanare River drainage is presented here, as an effort to contribute to the knowledge of its composition and richness, and to structure a base-line of the fish species found in the hydrographic drainage.

Material and methods

Study site

The main tributary of the Orinoco River in Colombia is the Meta River, which has an extensive system of tributaries that drain the Andes Mountains (Casanare, Ariporo, Cusiana, Cravo Sur, Pauto, Túa, Upía and Guachiría rivers). The Casanare River, with an extension of 8000 km2, originates in El Cocuy Natural National Park at 3685 m a.s.l (06°18’N, 072°21’W), and joins with the Ariporo River at 85 m a.s.l (06°03’N, 069°53’W) (IGAC 1999). The Casanare River drainage includes several different natural habitat units (Andean mountain, piedmont and savannah or llanos areas) and aquatic ecosystems (streams, rivers, wetlands and morichales) (Garavito-Fonseca et al. 2011) that drain part of the territory in the departments of Boyacá, Casanare and Arauca. The annual hydrological cycle of the drainage is unimodal with maximum rainfall through June-July, and minimum during January- February. The average monthly temperature is 25,9 °C and the precipitation 298,3 mm (IDEAM 2016 http:// www.ideam.gov.co/web/tiempo-y-clima/clima).

This study considered two natural units, the Andean piedmont that comprises the Andean versant above 200 m a.s.l, and the savannahs and flooded forests below 200 m a.s.l (Lasso et al. 2010). For the delimitation of natural units, the layer intersection tool was used (slope, geo-shape, covers and climate), available in ArcGIS ©10.2 (Figure 1).

Data Collection and Treatment

Samplings took place during two hydrological seasons: low water (March-April 2015) and high water (August- September 2015). The collections were carried out at 35 sampling localities in the Casanare River drainage including rivers, streams, lakes, floodplain lagoons and morichales, of which 24 are in the piedmont and 11 in flooded savannahs (Figures 2–11). The coordinates follow the WGS84 system.

Collection in piedmont stations was carried out with transects of 75 meters in length using an electrofishing equipment (Samus 725G/550-600), complemented with six successive passes of a seine (5 m long, 2 m height and 0,1 cm mesh) and 20 throws of a cast net (3 m diameter and 2 cm mesh). In the savannah stations, sampling spanned a transect of 100 m, performing eight passes of a seine (7 m long, 2 m height and 0,1 cm mesh), 20 throws of cast net (diameter of 4 m and 2,5 cm mesh) and the installation of 20 hooks during two hours (hooks and lines of different size and bait types). Two “stationary” gillnets (23 m long, 2 m height and 5 cm mesh) were used along the main course of the Casanare River, which were installed during 4 hours and examined every half hour.

The specimens were anesthetized in-situ with benzocaine solution and fixed in 10 % formalin, and then preserved in 70 % ethanol. Specimens were identified and housed in the ichthyological collections of both the Instituto Alexander von Humboldt (IAvH-P) and the Museo Javeriano de Historia Natural Lorenzo Uribe Uribe S.J (MPUJ). Large-sized species and those under any national threat category, were identified in the field, photographed and posteriorly released in their capture site. Taxonomic identification was done at the species level using species descriptions, taxonomic revisions and specialized taxonomic keys (Lasso and Machado-Allison 2000, Vari and Harold 2001, Taphorn 2003, Armbruster 2003, 2005, Netto-Ferreira et al. 2009, Londoño-Burbano et al. 2011, Ballen and Vari 2012, Ballen and Mojica 2014, Menezes and Lucena 2014, Marinho and Langeani 2016). The list of species and the validation of the scientific names follow the classification of Eschmeyer et al. (2016 http:// www.calacademy.org/scientists/catalog-of-fishesclassification/).

Species were categorized as endemic of Orinoco river drainage or some sub-drainage (Machado-Allison et al. 2010), migratory (Zapata and Usma 2013) and threatened (Mojica et al. 2012), in order to assess the conservation status of the fish fauna in the drainage.

Lastly, the complete dataset was uploaded to SiB Colombia’s (GBIF Colombia Node) Integrated Publishing Tool in order to increase the visibility and reach of the information produced herein. The Darwin Core standard (Wieczorek et al. 2012) was used as the biodiversity standard to structure the complete dataset. The shared dataset is identified by a DOI, provided by SiB Colombia and is available at http:// doi.org/10.15472/fjsg8q. All the results and discussion showed herein follow the version 2.2 of the published dataset.

Results

We recorded 180 fish species belonging to 110 genera, 33 families and seven orders. The order Characiformes was the richest with 92 species followed by the Siluriformes with 68, Gymnotiformes with 9 and the Cichliformes with 8, while the Myliobatiformes, Synbranchiformes and Cyprinodontiformes were represented by one species each (Figures 12–65). Of these species, 41 are exclusive to the piedmont, 83 to the savannah and 56 are shared between both natural units. We found 27 species with taxonomic uncertainty that are in revision process, three are presumably undescribed species: Andinoacara sp. (Figure 12), Chaetostoma sp. (Figure 13) and an undetermined genus of Heptapteridae. Epapterus blohmi is herein reported as a new record for the Orinoco River Basin in Colombia.

Likewise, 19 species are endemic to the Orinoco River Basin, 11 are migratory (Figures 14–22) and three categorized as threatened: Pseudoplatystoma metaense (Figure 15) and P. orinocoense (Figure 16) are Vulnerable-VU and Potamotrygon orbignyi (Figure 23) is Near Threatened-NT.

Discussion

The highest diversification of the freshwater fish species took place in the tropical and subtropical regions, as a result of climatic and environmental processes and ecological factors (Levêque et al. 2008, Winemiller 2008). Among freshwater groups, the Characiformes and Siluriformes are the most diversified and representative taxa of the Neotropical ichthyofauna (Albert and Reis 2011, Reis et al. 2016), which has been studied at different spacial scales (Lasso et al. 2004, Urbano-Bonilla et al. 2009, 2014, Villa-Navarro et al. 2011, Maldonado-Ocampo et al. 2013). In this study the same pattern was observed, where Characiformes and Siluriformes represent 89,1 % of recorded species.

Urbano-Bonilla et al. (2009) reported 15 species for the piedmont natural unit of the Casanare River drainage, while in this study the number increased to 97. This richness is higher than that found for the piedmont in other adjacent drainages such as the Pauto (58 spp.), Túa (49 spp.) and Upía river (45 spp.) (Urbano- Bonilla et al. 2009). This is the first contribution to the knowledge of the fishes found in the savannah natural unit in the Casanare River drainage with 139 species. These results highlight the importance of the multispatial and multi-temporal inventories that improve our knowledge about community composition, which can not be successfully recorded by means of isolated punctual samplings. Such approach is even more relevant for areas with highly diverse and speciose faunas such as the Orinoco River Basin (Lasso et al. 2016).

Villa-Navarro et al. (2011) found 20 fish species for the Casanare River drainage, while Usma et al. (2016) recorded only three species in the drainage. In this study we found 180 species, placing the Casanare River as the second drainage in species richness of freshwater fishes within the Meta River drainage, surpassed only by the Cusiana River, with 258 species (Usma et al. 2016). Although some patterns of fish distribution and richness have been reported for piedmont rivers (Urbano- Bonilla et al. 2009, 2014), savannahs (Hoeinghaus et al. 2004, Arrington and Winemiller 2006) and shared environments (Willis et al. 2005), the present contribution complements previous studies on the ichthyofauna of the Casanare River drainage. However, similar efforts are still needed in order to characterize the species composition in the upper (more than 1000 m a.s.l) and lower portions of the drainage (below 150 m a.s.l). Such biological assessment studies are important given the strong anthropogenic impact present in these areas (i.e., land conversion due to colonization, mining, agricultural and livestock), factors with a direct impact on the composition, richness and function of the fish community due to habitat loss (Machado-Allison et al. 2011, Barletta et al. 2016, Lasso et al. 2016, Reis et al. 2016, Toussaint et al. 2016).

Fish species richness in the Casanare River drainage represents 27,3 % of that reported for the Orinoco River Basin in Colombia, including a new record, three presumably undescribed species, 19 endemics, 11 migratory and three categorized as threatened. This information about the ichthyofauna present in the drainage is useful, considering that conservation efforts are focused on prioritized areas according to the level of knowledge about richness, endemism, threats and importance for human communities (Machado-Allison et al. 2010, Trujillo et al. 2011, Portocarrero-Aya et al. 2014). Therefore, our results contribute to filling some knowledge gaps on the fish communities of the Casanare River drainage, and highlight its importance as a potential area for biodiversity conservation. In addition, this information is expected to allow environmental authorities to develop and implement management plans for a series of human activities such as fishing and hydrobiological resource use in the drainage.

Conclusion

The natural eco-regions of Orinoco Piedmont and Savannahs or Orinoco Llanos, have unique attributes of resources and microhabitat availability and water types, which facilitate the refuge, dispersion and reproduction for a high number of freshwater fish species. This study highlights the importance of performing ichthyological explorations in poorly sampled environments, as it contributes to the baseline to knowledge of biodiversity and serves as a tool for regional environmental authorities as CORPORINOQUIA, to formulate the Plan for the Management of the Casanare River drainage. In addition, this information is key to identify conservation priorities for migratory, endemic or endangered species and priority areas or drainages for conservation, in the process of selection and enactment of national protected areas in Colombia.

Acknowledgments

This investigation was carried out within the framework of the research permit 500-41-15.07209 of CORPORINOQUIA, and throught the agreement 15-14-172-010CE with the Instituto de Investigación de Recursos Biológicos Alexander von Humboldt (IAvH). The authors thank the Fundación Reserva Natural La Palmita for financial support through the Cooperation agreement No. 15-14-172-010CE and the consultancy contract No. 1918-2014 with the departmental government of Casanare. We are also grateful to Maria Isabel Vieira, Carolina Mora and Miguel E. Rodríguez- Posada for technical and administrative support. To Saúl Prada and Javier Maldonado-Ocampo in the Pontificia Universidad Javeriana, and Carlos DoNascimiento in the Instituto Alexander von Humboldt for their support in the fish collections. Carolina Galindo, Liz Ladino, Lina Camacho, Kelly Triana, Guido Herrera, Alejandro Méndez and Bienvenido Bastidas provided support in field and during lab work. Gustavo A. Ballen and two anonymous referees are acknowledged for reviewing the English and their comments on the manuscript. Finally, we thank the local experts from the municipalities of Tame-Arauca (Julio Ramírez, Nelson Fonseca, María Moreno, Iván Medina, Enrique Contreras, Iraida Cantor and York Jaider Vera) and Hato Corozal-Casanare (Aldiver Reyes and Giovanni Martínez) who actively participated in the field sampling as part of the Environmental Strengthening Community Programe of Fundación La Palmita.

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