Abstract

The ichthyofauna of the upper reaches of the Meta River, one of the main tributaries of the Orinoco, is still poorly known. This paper presents the first list of fishes recorded for the Ocoa River, based on 51 901 individuals sampled in 15 localities during the 2014 hydrological cycle, including urban areas in the municipality of Villavicencio. Records of 88 species were obtained, distributed in 21 families and 5 orders, corresponding to 12% of the freshwater species reported for the Colombian Orinoquia. The estimated sampling coverage (SC) for the Ocoa River was 99.9%, with an observed species richness representing 93.6% of the expected richness. Among the species collected, 13 are reported only for Colombia, 43 have fishery use and four species are introduced (Caquetaia kraussii, Oreochromis niloticus, Poecilia reticulata and Poecilia cf. caucana). The latter dominate in disturbed sites with low oxygen levels. This study constitutes the first approximation to the knowledge of the ichthyofauna of one of the most important sub-basins for the municipality of Villavicencio.

Keywords: Colombia; biodiversity; inventory; freshwater fish; water quality; invasive species.

Resumen

Ictiofauna de la subcuenca urbana del río Ocoa, drenaje superior del río Meta, cuenca del Orinoco, Colombia

El conocimiento acerca de la ictiofauna de los tramos altos del río Meta, uno de los principales afluentes del Orinoco, es aún poco conocida. En este trabajo se presenta el primer listado de peces registrados para el río Ocoa, a partir de 51 901 individuos muestreados en 15 localidades durante el ciclo hidrológico de 2014, incluidas zonas urbanas en el municipio de Villavicencio. Se obtuvieron registros de 88 especies, distribuidas en 21 familias y 5 órdenes, lo que corresponde al 12% de las especies de agua dulce reportadas para la Orinoquia colombiana. La cobertura de muestreo (SC) estimada para el río Ocoa fue del 99.9%, con una riqueza de especies observada que representa el 93.6% de la riqueza esperada. Entre las especies recolectadas, 13 están reportadas solo para Colombia, 43 tienen uso pesquero y cuatro especies son introducidas (Caquetaia kraussii, Oreochromis niloticus, Poecilia reticulata y Poecilia cf. caucana). Estas últimas dominan en sitios alterados con bajos niveles de oxígeno. Este estudio constituye la primera aproximación al conocimiento de la ictiofauna de una de las subcuencas de mayor importancia para el municipio de Villavicencio.

Palabras clave: Colombia; biodiversidad; inventario; peces de agua dulce; calidad del agua; especies invasoras.

Recibido/Received: 26/10/2022; Aceptado/Accepted: 05/06/2023; Publicado en línea/Published online: 02/10/2023

Cómo citar este artículo/Citation: Ramírez-Gil, H., Cortés-Hernández, M.A. & Ajiaco-Martínez, R.E. 2023. Ichthyofauna of the urban sub-basin of the Ocoa River, Upper Meta River drainage, Orinoco Basin, Colombia. Graellsia, 79(2): e197. https://doi.org/10.3989/graellsia.2023.v79.378

Copyright: © 2023 SAM & CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License.

Introduction [Up]

The Meta River is one of the largest tributaries of the Orinoco River, with a basin that covers 10830.4 km2 (‍Machado-Allison et al., 2010), sheltering a richness of 577 fish species (‍Usma et al., 2016), equivalent to 79.3% of the native species of the Orinoco (‍DoNascimiento, 2021). Previous studies have documented the fish fauna of tributaries originating in the foothill part of this basin, with 115 species reported for the Cusiana, 96 for the Cravo Sur River, 49 for the Túa River, 45 for the Upía River and 10 for the Guachiría River (‍Urbano-Bonilla et al., 2009), and 113 species in the Orotoy River (‍Ramírez-Gil et al., 2011), 180 for the Pauto River (‍Maldonado-Ocampo et al., 2013), 241 for the Cusiana River (‍Urbano-Bonilla et al., 2018) and 180 for the Casanare River (‍Zamudio et al., 2017). However, there are still information gaps for some drainages and small streams in the upper Meta River (‍Zamudio & Maldonado-Ocampo, 2021), an area highly impacted by changes in land use (e.g., deforestation, agriculture, livestock, hydrocarbon exploitation, and urbanization), and biodiversity loss (‍Machado-Allison et al., 2010).

The Ocoa River, a tributary of the Guatiquia River, is one of the most important watersheds for the municipality of Villavicencio, providing water resources for human consumption, as well as for agricultural, forestry and mining uses of rural settlements (‍Osorio-Ramírez et al., 2015). In addition, it provides food resources (e.g., fishing for consumption) for the most vulnerable communities (Ramírez-Gil pers. obs.). However, the Ocoa River is the main recipient of more than 100 discharges from the urban center, serving as a sink for 80% of urban wastewater (Osorio-Ramírez et al., 2015), promoting degradation and ecological loss of the riverbed (‍Aguilera-Giraldo et al., 2019; ‍Rojas-Peña et al., 2021).

Faced with this panorama of anthropic intervention, we conducted surveys to characterize the fish fauna subsisting in this river and document key areas for native species. With the knowledge of the ichthyic biodiversity of the Ocoa River, we also contribute to the knowledge of the ichthyofauna of the Orinoco River basin.

Material and methods[Up]

Study site

The Ocoa River is a lotic ecosystem of the second order, located in the piedmont of the Eastern Cordillera of the Andes, with a basin of 282.2 km2 and 68.55 km in length, of which 17 km run through the urban area of the municipality of Villavicencio, a city with an estimated population of 451 212 inhabitants (‍Departamento Administrativo Nacional de Estadísticas - DANE, 2018). It originates in the southwest of the municipality, in the Samaria village at 1155 m a.s.l., and flows into the Guatiquia River between the Guamo and Indostán villages at 225 m a.s.l. (‍Osorio-Ramírez et al., 2015). The annual hydrological cycle of the Ocoa River is unimodal, with minimum rainfall between December-March and a rainy period between April and November with maximum precipitation during April-July (‍Instituto de Hidrología, Metereología y Estudios Ambientales - IDEAM, 2022). The average temperature range is 15.5–33.5 °C and average annual rainfall is 2700–5000 mm (‍Osorio-Ramírez et al., 2015).

Data collection and treatment

To obtain samples of the fish community assemblages, spatial and temporal collections were made in the Ocoa River during the 2014 annual hydrological cycle. A total of 15 locations were sampled, eight along the main channel and seven in the micro-basins that are tributary to the main channel (Fig. 1); four samples were taken in each site (Table 1). Stations 3 to 6 correspond to the river’s transit through the urban zone of Villavicencio. The fish were captured by electric fishing, following the methodology proposed by Ramírez-Gil et al. (‍2011). Simultaneously, some environmental variables were recorded in situ, including water temperature (ºC), pH, dissolved oxygen (mg/l) and electrical conductivity (μS/cm) using multiparametric equipment.

Fig. 1.— Map of the Ocoa River drainage with the distribution of the sampling stations.

Fig. 1.– Mapa de la subcuenca del río Ocoa con la distribución de las estaciones de muestreo.

mediumimage/graellsia-79-2-e197-image1.png

Table 1.— Temporal distribution of sampling sessions in the fifteen localities sampled.

Tabla 1.– Distribución temporal de los muestreos realizados en las quince localidades estudiadas.

Month Sampling sites
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
February 1 1 1 1 1 1 1
March 1 1 1 1 1 1 1 1
May 1 1 1 1 1 1 1 1 1 1 1 1
June 1 1
August 1 1 1 1 1 1 1 1 1
September 1 1 1 1 1
November 1 1 1 1 1 1 1 1 1 1 1 1 1 1

The captured fish were anesthetized and sacrificed in a clove oil solution (Eugenol 300 mg/l), fixed in 10% formaldehyde, and preserved in 70% ethanol. For species identification, specialized taxonomic keys, original descriptions, and taxonomic revisions were used (e.g., ‍Eigenmann & Fisher, 1916; ‍Eigenmann, 1917, ‍1922; ‍Myers, 1927; ‍Schultz, 1944; ‍Nijssen & Isbrücker, 1980; ‍Mees, 1988; ‍Vari, 1991; ‍Lasso & Machado-Allison, 2000; ‍Mago-Leccia et al., 2001; ‍Taphorn, 2003; ‍Londoño-Burbano et al., 2011, ‍2018; ‍Ballen & Vari, 2012; ‍Ballen et al., 2016; ‍Marinho & Menezesm 2017; ‍Armbruster et al., 2018; ‍Kullander et al., 2018; ‍Urbano-Bonilla et al., 2018; ‍Urbano-Bonilla & Ballen, 2021; ‍Lima, 2022). The taxonomic status of species was validated in Eschmeyer’s Catalog of Fishes (‍Fricke et al., 2022), and to verify thepresence of these species in the national territory, the list of freshwater fish species of Colombia (‍DoNascimiento et al., 2021), was reviewed. Later, the lots of collected specimens were deposited in the ichthyological collection of the Unillanos Natural History Museum - MHNU-I.

Statistical analyses

To calculate the interpolation and extrapolation of the species richness in the Ocoa River drainage, an analysis of the effective number of species was carried out based on the first number of the Hill series (q = 0) as suggested by Jost (‍2006) and Jost & González-Oreja (‍2012). In addition, the completeness of the sampling coverage (SC) was calculated, which allows the evaluation of the sampling effort (‍Chao & Jost, 2012; ‍Chao et al., 2014). All these analyses were carried out in the iNEXT package (‍Hsieh et al., 2020) in R (‍R Development Core Team, 2022).

Results[Up]

In total, 51 901 specimens were collected, grouped in five orders, 21 families, 61 genera, and 88 species (Table 2). The most representative orders in captures were Siluriformes, with eight families, 26 genera and 38 species, followed by Characiformes, with seven families, 24 genera and 37 species (Table 3). The families with the greatest richness and abundance were Characidae (26 species, 29.5%; n = 20058, 38.6%), Loricariidae (17 species, 19.3%; n = 1327, 2.6%), Heptapteridae (10 species, 11.4%; n = 836, 1.6%), and Cichlidae (7 species, 8.0%; n = 2087, 4.0%) (Fig. 2). The Poecilidae family was the most representative, with an abundance of 26 501 individuals (51.1%), with Poecilia reticulata (n = 3717) and Poecilia cf. caucana (n = 22 784) being the most abundant species of all samples.

Fig. 2.— Abundance and richness of species of the family collected in the Ocoa River.

Fig. 2.– Abundancia y riqueza de especies de las familias recolectadas en el río Ocoa.

mediumimage/graellsia-79-2-e197-image2.png

Table 2.— Species captured during the hydrological cycle of 2014 in the Ocoa River, with their abundance (n) and catalog number of the ichthyological collection of the Museo de Historia Natural Unillanos. Abbreviation: * species endemic to Colombia; ** migratory species; + introduced species; Or - species of ornamental use; Fi - species consumed as food.

Tabla 2.– Especies capturadas durante el ciclo hidrológico de 2014 en el río Ocoa, con su abundancia (n) y número de catálogo de la colección ictiológica del Museo de Historia Natural Unillanos. Abreviatura: * especie endémica de Colombia; ** especies migratorias; + especies introducidas; Or - especies de uso ornamental; Fi - especies que se consumen como alimento.

Order/family/species n Use MHNU-I
Characiformes
Crenuchidae
Characidium cf. boavistae Steindachner, 1915 10 1140
Characidium steindachneri Cope, 1878 19 2734
Characidium zebra Eigenmann, 1909 250 Or 2665
Characidium sp. 159 2666
Erythrinidae
Hoplerythrinus unitaeniatus (Spix & Agassiz, 1829) 1 Or/Fi 3082
Hoplias malabaricus (Bloch, 1794) 30 Or/Fi 1884
Parodontidae
Parodon apolinari Myers, 1930 1 Or 2152
Curimatidae
Steindachnerina argentea (Gill, 1858) 5 1481
Steindachnerina guentheri (Eigenmann & Eigenmann, 1889) 3 2040
Lebiasinidae
Copella eigenmanni (Regan, 1912) 10 Or 971
Bryconidae
Salminus hilarii Valenciennes, 1850** 1 Fi 1831
Characidae
Aphyocharax pusillus Günther, 1868 3 Or 3084
Astyanax aff. bimaculatus (Linnaeus, 1758) 144 1482
Astyanax integer Myers, 1930 3 3092
Astyanax metae Eigenmann, 1914 2 980
Astyanax venezuelae ‍Schultz, 1944 12 -
Ceratobranchia sp. 283 1074
Charax metae ‍Eigenmann, 1922 2 Or 1934
Cheirodontops geayi ‍Schultz, 1944 20 1261
Corynopoma riisei Gill, 1858 12 Or 3087
Creagrutus taphorni Vari & Harold, 2001 7047 2376
Ctenobrycon spilurus (Valenciennes, 1850) 1 Or 3094
Gephyrocharax valencia Eigenmann, 1920 18 3088
Hemibrycon loisae (Géry, 1964) 8634 1478
Hemibrycon metae Myers, 1930 10 1441
Hemigrammus barrigonae Eigenmann & Henn, 1914 15 Or 3224
Hemigrammus marginatus Ellis, 1911 5 1488
Hemigrammus sp. 2 973
Hyphessobrycon metae Eigenmann & Henn, 1914 2 Or 2041
Knodus alpha (Eigenmann, 1914) 2 1539
Knodus cismontanus (Eigenmann, 1914) 3761 1444
Knodus sp. 3 981
Moenkhausia oligolepis (Günther, 1864)** 5 Or 2042
Moenkhausia sp. 2 1584
Odontostilbe splendida Bührnheim & Malabarba, 2007 63 1537
Paragoniates alburnus Steindachner, 1876 6 Or 3085
Roeboides dientonito ‍Schultz, 1944 1 1259
Gymnotiformes
Apteronotidae
Apteronotus galvisi de Santana, Maldonado-Ocampo & Crampton, 2007* 16 1988
Sternopygidae
Eigenmannia sp. 8 3096
Siluriformes
Trichomycteridae
Ochmacanthus alternus ‍Myers, 1927 37 984
Trichomycterus cf. knerii Steindachner, 1882 376 956
Callichthyidae
Corydoras melanotaenia Regan, 1912* 3 2045
Corydoras metae Eigenmann, 1914* 9 2745
Corydoras simulatus Weitzman & Nijssen, 1970* 10 2047
Hoplosternum littorale (Hancock, 1828) 1 Or/Fi 1835
Loricariidae
Ancistrus triradiatus Eigenmann, 1918 60 Or 990
Chaetostoma chimu ‍Urbano-Bonilla & Ballen, 2021* 11 1153
Chaetostoma dorsale Eigenmann, 1922 41 Or 988
Chaetostoma formosae Ballen, 2011* 568 1152
Chaetostoma sp. 7 1595
Dolichancistrus fuesslii (Steindachner, 1911)* 72 1323
Farlowella mariaelenae Martín Salazar ,1964 49 Or 1268
Farlowella vittata Myers, 1942 163 Or 987
Hypostomus niceforoi (Fowler, 1943)* 250 Or 1068
Hypostomus plecostomoides (‍Eigenmann, 1922) 13 Or/Fi 2568
Lasiancistrus tentaculatus Armbruster, 2005 6 1272
Loricariichthys brunneus (Hancock, 1828) 7 Or 1923
Nannoptopoma spectabile (Eigenmann, 1914) 21 Or 986
Otocinclus vittatus Regan, 1904 17 Or 2713
Panaqolus maccus Schaefer & Stewart, 1993 25 Or 1154
Rineloricaria eigenmanni (Pellegrin, 1908) 13 Or 1560
Spatuloricaria terracanticum ‍Londoño-Burbano, Urbano-Bonilla, Rojas-Molina, Ramírez-Gil & Prada-Pedreros, 2018 4 Donation
Astroblepidae
Astroblepus sp. 1 6 1324
Astroblepus sp. 2 46 958
Cetopsidae
Cetopsis orinoco (‍Schultz, 1944)** 14 1157
Aspredinidae
Bunocephalus aloikae Hoedeman, 1961 14 Or 1995
Auchenipteridae
Duringlanis romani (‍Mees, 1988) 53 966
Heptapteridae
Cetopsorhamdia cf. insidiosa (Steindachner, 1915) 1 1159
Cetopsorhamdia orinoco ‍Schultz, 1944 58 Or 1160
Chasmocranus rosae ‍Eigenmann, 1922* 284 948
Heptapteridae gen. nov. 5 1161
Imparfinis microps ‍Eigenmann & Fisher, 1916* 3 3229
Imparfinis pseudonemacheir Mees & Cala, 1989 2 992
Imparfinis cf. guttatus (Pearson, 1924) 16 951
Nemuroglanis mariai (‍Schultz, 1944)* 3 1950
Pimelodella metae ‍Eigenmann, 1917 240 993
Rhamdia laukidi Bleeker, 1858 224 Fi 1379
Synbranchiformes
Synbranchidae
Synbranchus marmoratus Bloch, 1795 8 Or 1507
Blenniiformes
Cichlidae
Aequidens metae ‍Eigenmann, 1922 1 Or/Fi 2397
Bujurquina mariae (‍Eigenmann, 1922)* 1336 Or/Fi 995
Bujurquina sp. 1 -
Caquetaia kraussii (Steindachner, 1879)+ 28 Fi 1167
Crenicichla geayi Pellegrin, 1903 60 Or 994
Mikrogeophagus ramirezi (Myers & Harry, 1948) 1 Or 2758
Oreochromis niloticus (Linnaeus, 1758)+ 660 Fi 1070
Rivulidae
Rivulus tessellatus Huber, 1992* 2 2104
Poeciliidae
Poecilia reticulata Peters, 1859+ 3717 Or 2506
Poecilia cf. caucana+(Steindachner, 1880) 22784 1398

Table 3.— Number and percentage of families, genera and species for each of the orders present in the Ocoa River.

Tabla 3.– Número y porcentaje de familias, géneros y especies para cada uno de los órdenes presentes en el río Ocoa.

Orders Family % Genus % Species %
Siluriformes 8 38.1 26 42.6 38 43.2
Characiformes 7 33.3 24 39.3 37 42.0
Blenniiformes 3 14.3 8 13.1 10 11.4
Gymnotiformes 2 9.5 2 3.3 2 2.3
Synbranchiformes 1 4.8 1 1.6 1 1.1
Total 21 100 61 100 88 100

Among the captured species, 12 are endemics to the Orinoco River basin. In addition, 33 species are used in ornamental fishing and ten in consumption fishing. Cetopsis orinoco, Moenkhausia oligolepis and Salminus hilarii are migratory species (‍DoNascimiento et al., 2021) and four species are introduced to the Orinoco River basin (Caquetaia kraussii, Oreochromis niloticus, Poecilia cf. caucana and Poecilia reticulata). Poecilia reticulata and Poecilia cf. caucana. were more abundant (n > 700 individuals) on stations 5 and 6, the sites with greater anthropogenic influence, where measures of dissolved oxygen ranged from 0.3–6.3 mg/l and conductivity between 135.3–222.5 µS/cm. It is worth noting that in station 6, the one with the lowest species diversity during the dry season, only four species (three of them alien) were reported: Poecilia cf. caucana, Poecilia reticulata, Oreochromis niloticus, and the native species Characidium zebra, with a strong dominance of Poecilia cf. caucana, that represented 83% of the individuals collected at that site, while the native species only represented 0.6%.

The completeness of the sampling coverage (SC) for the Ocoa River was 99.9%, indicating that the sampling is representative of the local fish community. Extrapolation analyses suggest that the expected richness for the Ocoa River is approximately 94 species (95% CI = 89.5–113.7), with the observed richness representing 93.6% of the expected richness (Fig. 3).

Fig. 3.— Species accumulation curve of fishes in the Ocoa River. Abbreviations: S.obs = observed richness, S.est = estimated richness.

Fig. 3.– Curva de acumulación de especies de peces del río Ocoa. Abreviaturas: S.obs = riqueza observada, S.est = riqueza estimada.

mediumimage/graellsia-79-2-e197-image3.png

The physicochemical parameters recorded are summarized in Table 4. The temperature in the main channel ranged between 22.6 and 32.9 °C, and in the tributary channels between 16.9 and 27.2 °C. The pH gradient ranged from 4.2 to 7.8 in stations 1 to 5, and from 6.2 to 9.6 in the remaining stations, and in the tributaries between 4.2 and 10.8. Oxygen levels in general were between 0.3 and 7.8 mg/l, with the lowest levels found at stations 5 and 6 in the urban zone; in the tributaries, the variation was between 0.5 and 7.8 mg/l. The highest conductivity value was reported at station 12, which corresponds to a tributary.

From stations 3 to 6, corresponding to the section of the river in the urban area, the forest cover has been replaced by houses on both sides of the river, some of them with direct discharge of their domestic wastewater.

Table 4.— Physicochemical data measured in 15 sampling stations on the Ocoa River drainage. Abbreviations: Elev. – Elevation (m.a.s.l.); Temp. – Temperature (°C); DO – dissolved oxygen (mg/l); Cond.– electrical conductivity (μS/cm); * Tributaries.

Tabla 4.– Datos fisicoquímicos medidos en 15 estaciones de muestreo en la subcuenca del río Ocoa. Abreviaturas: Elev. – Elevación (m s.a.l.); Temperatura. – Temperatura (°C); DO – oxígeno disuelto (mg/l); Cond.– conductividad eléctrica (μS/cm); * Tributarios.

Stations Elev. Temp. pH DO Cond. Coordinates
1 451 24.0-26.3 5.6-6.3 2.7-7.3 23.0-27.5 04°04'6.1''N 73°42'38''W
2* 453 22.6-26.3 4.2-5.7 3.0-7.7 47.9-126.8 04°04'54.2''N 73°42'30.1''W
3 423 24.0-27.3 5.6-7.8 2.4-7.0 47.9-65.5 04°04'56.5''N 73°40'30''W
4 397 24.0-26.4 6.0-7.7 0.3-7.1 54.0-104.9 04°06'13.5''N 73°37'58.9''W
5 397 23.7-30.8 5.7-7.6 1.5-2.1 94.8-222.5 04°06'43''N 73°36'20.5''W
6 369 23.5-30.8 6.4-8.1 0.3-3.3 135.3-211.7 04°06'49.5"N 73°34'22.1"W
7 299 23.6-32.9 6.6-9.6 0.5-5.8 59.2-243.7 04°07'12''N 73°25'56''W
8 273 26.7-29.6 6.7-8.2 1.6-6.3 96.0-301.7 04°07'8''N 73°21'46.1''W
9 259 24.3-27.6 6.2-7.7 2.6-4.2 87.4-209.4 04°07'30.2''N 73°15'24.12''W
10* 563 16.9-24.0 6.8-10.8 3.4-7.8 50.1-199.0 04°08'16.93''N 73°39'18.88''W
11* 521 22.8-24.5 6.9-7.9 3.1-7.6 64.1-162.8 04°08'13.3''N 73°38'45.3''W
12* 395 24.5-27.2 6.5-7.2 0.5-6.3 182.4-488.0 04°07'5.84''N 73°37'23.1''W
13* 454 21.8-24.3 7.3-8.5 2.2-5.3 210.0-271.5 04°06'24.74''N 73°39'53.55''W
14* 414 21.3-24.0 6.3-8.6 1.4-6.3 196.6-241.8 04°06'24''N 73°39'0.6''W
15* 461 23.4-26.0 6.9-8.8 1.9-4.3 52.5-83.4 04°08'24.43''N 73°38'53.37''W

Discussion[Up]

The present study constitutes the first approximation to the knowledge of the ichthyofauna of the Ocoa River, which crosses the municipality of Villavicencio, with a species richness representing 63.7% of the species listed for the Guatiquia River (‍Zamudio & Maldonado-Ocampo, 2021), 15.2% for the Meta River drainage (‍Usma et al., 2016), and 12% of those recorded in the Orinoco basin, a figure estimated at 722 species (‍DoNascimiento et al., 2021). The extrapolation suggests that the drainage could have about 94 species, with a high percentage of the expected richness (93.6%) recovered in our surveys.

The composition of the fish assemblage of the Ocoa River was mainly dominated by Characiformes and Siluriformes, contributing 85% of the total species recorded for this drainage (Fig. 2), similarly to other drainages of the Colombian Orinoco River Basin (e.g., ‍Urbano-Bonilla et al., 2009, ‍2014, ‍2018; ‍Ramírez-Gil et al., 2011; ‍Villa-Navarro et al., 2011; ‍Maldonado-Ocampo et al., 2013; ‍Usma et al., 2016; ‍Zamudio et al., 2017) and the Neotropics (e.g., ‍Albert & Reis, 2011; ‍Reis et al., 2016; ‍Van der Sleen & Albert, 2018). Regarding higher taxonomic levels, our results suggest some impoverishment in the Upper Meta communities, with representatives of five of the thirteen orders registered for the Orinoquia, a figure that is usually higher (6-‍9) in other rivers of the region, and 20 native families out of the 50 registered for the area (‍Urbano-Bonilla et al., 2009; ‍Ramírez-Gil et al., 2011; ‍Maldonado-Ocampo et al., 2013; ‍DoNascimiento et al., 2021).

The Poecilidae family was the most representative in terms of abundance, surpassing the Characidae and Loricariidae families (Table 2). This is probably due to the successful biological adaptations of Poecilia species (e.g., early reproductive maturity, sperm storage, superfetation, air-breathing ability, and high thermal tolerance), that make them highly tolerant eurytropic species (‍Jiménez-Prado et al., 2020; ‍López-Fuentes et al., 2021), proliferating and dominating over native species, as reported by Casatti et al. (‍2009) for the Saõ Josẽ dos Dourados and Turvo-Grande rivers in Brazil.

Four introduced species Caquetaia kraussii, Poecilia cf. caucana, Poecilia reticulata and Oreochromis niloticus were collected in the sites with the greatest environmental degradation, influenced by urbanization and pollution, which favors the establishment of alien species, since habitat degradation negatively affects native species and facilitates the success of invasions (‍Hooper et al., 2005). According to Royero & Lasso (‍1992), C. kraussii was possibly introduced to the Orinoco River basin by escapes from fish farms, as reported for O. niloticus, which is widely distributed in 21 river basins worldwide (‍Agostinho et al., 2021). In addition, P. reticulata and P. cf. caucana were possibly introduced deliberately by aquarists (‍Claro-García et al., 2017). Previous fish assessments in foothill rivers in the region did not report introduced species (‍Urbano-Bonilla et al., 2009, ‍2018; ‍Ramírez-Gil et al., 2011; ‍Maldonado-Ocampo et al., 2013; ‍Zamudio et al. 2017, ‍2021), this being the first records of their presence, highlighting the environmental deterioration of this river to the detriment of native species.

On the other hand, our surveys also recovered individuals from 11 morphospecies (e.g., Characidium sp., Ceratobranchia sp., Hemigrammus sp., Eigenmannia sp., Chaetostoma sp., Astroblepus spp., Heptapteridae gen. nov., Bujurquina sp.), that possibly represent new species, which requires further, in-depth taxonomic studies to elucidate their status and present a more complete picture of the actual species diversity in the basin.

The present study was carried out during a single hydrological cycle (2014), but there is a need to continue sampling efforts in the Ocoa River; since monitoring information is important to understand how different anthropogenic activities are affecting environmental conditions and freshwater communities, allowing the design and implementation of conservation strategies for the drainage.

Acknowledgments[Up]

The authors would like to thank Universidad de los Llanos for the funding and support for this work, through the agreement 5211594 signed between Unillanos and Ecopetrol and the project “Design and implementation of an electronic prototype based on DC-AC cycle converters and photovoltaic solar energy useful for electric fishing in low conductivity waters”, code C8-F02-003-2019. Also, we thank Elizabeth Aya Baquero, curator of the Unillanos Natural History Museum for the management of the biological material.

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