Over 330 fish species -- up to 35 new to science -- found in Bolivian national park

The study lists the fish species whose presence in Madidi has been confirmed, including those recorded during the Identidad Madidi expeditions, and a compilation of species occurrences listed in previous studies, providing an estimate of the total ichthyological richness for this protected area. The species list for the Madidi protected area includes 35 possible new species for science.

Species range in size from the invasive arapaima (Arapaima gigas), a mouth breathing giant weighing in at more than 200 kg and more than 3 m long, to the seasonally abundant killifish (Anablepsoides beniensis) from the Rivulidae family found in pools in natural savannas that are just 1.5 cm long. The list also includes the most attractive gamefish from the Amazon, the golden dorado (Salminus brasiliensis), as well as migratory catfish from the Amazonian goliath catfish (Brachyplatystoma filamentosum) to the tiny chipi chipi pencil catfish whose massive collective migration is a local phenomenon (Trichomycterus barbouri). Another killifish (Orestias sp.) is found in some of the highest Andean lakes at 4,300 m in Madidi, whilst in the stagnant ponds of the wonderful Amazon electric knife fish (Gymnotus carapo) and the swamp eel (Synbranchus madeirae), and in the fast-flowing streams of the Amazon headwaters, several species of naked catfish (Astroblepus spp.), including probable several new species for science.

The 35 possible new species for science includes candidates of the genus Knodus, Microgenys, Moenkhausia, Characidium, Apareiodon, Brachyhypopomus, Ernstichthys (genus reported for the first time in Bolivia), Astroblepus, Trichomycterus (including one species recently described and named in honor of a pioneer French ichthyologist in Bolivia), and a three-barbled catfish (Cetopsorhamdia), a striking pike cichlid (Crenicichla) and a charming bumblebee catfish (Microglanis), among others.

The biodiversity surveys and field research were conducted between 2015 to 2018 by specialists from the Wildlife Conservation Society (WCS), the Institut de Recherche pour le Développement de Montpellier (France) and the National Museum of Natural History and the Ecology Institute of the Universidad Mayor de San Andrés. Madidi is probably the world's most biologically diverse protected area due to a unique altitudinal gradient of almost 6,000 m spanning the Tropical Andes and the Amazon.

For four years, the specialists conducted extensive ichthyological sampling at 13 sites in Madidi National Park, using different sampling techniques: electrofishing, gill nets, trawls, hook and line, and ichthyoplankton nets. Ichthyoplankton species were identified by genetic characterization (metabarcoding). A total of 333 species distributed in 43 families and 13 orders were recorded. This number doubles the previously known ichthyofauna (161) in Madidi.

The largest number of species are found in the order Characiformes (139 species; 41.7 percent), followed by Siluriformes (137 species; 41.1 percent), and Cichliformes (19 species; 5.7 percent), which together represent 88.6 percent of species richness. The remaining 11.4 percent is distributed in 10 other orders. The families with the highest number of species are the characids (73 species; 21.9 percent), loricariids (36; 10.8 percent), heptapterids (21; 6.3 percent), pimelodids (21; 6.3 percent) and cichlids (19; 5.7 percent).

Lead author of the study, Guido Miranda, of the Wildlife Conservation Society said "With an extension of 18,957.5 square kilometers (7,319 square miles), Madidi covers 1.3 percent of the Madeira River basin, but conserves 25 percent of the known species in the basin. Madidi also represents only 1.8 percent of the Bolivian territory, but it conserves almost 40 percent of the ichthyofauna recorded in Bolivia. This study has more than doubled our knowledge about fish diversity in this incredible protected area, but with several sub-basins yet to sample in the park, this is only the beginning."

Dr. Rob Wallace, Senior Conservation Scientist at the Wildlife Conservation Society, leader of the Identidad Madidi expeditions, and coauthor, said "Due to its great diversity of habitats, mostly as a result of the altitudinal gradient from 184 meters (Heath River) to 6,044 meters (Chaupi Orko Peak), Madidi is considered the most biodiverse protected area on the planet. The Identidad Madidi initiative aimed to firmly establish this record-breaking status for the park, whilst communicating the importance of Madidi to the Bolivian people. This is the first of several biodiversity summary articles that the Bolivian scientists on the expedition are systematizing to share the results of our efforts with Bolivia and the world."

Study authors include: Guido Miranda-Chumacero^{1, 3}, Jaime Sarmiento², Soraya Barrera², Martin Velasco², Jorge Molina-Rodriguez^1,3, Gabriel Tarifa³, Camila Ramallo³, Oscar Ayala³, Kelvin Herbas³, Erick Loayza³, Débora Alvestegui³, Gustavo Alvarez¹, Jean-François Renno⁴, Cédric Mariac⁴ & Robert B. Wallace¹

¹Wildlife Conservation Society, Bolivia Program, La Paz.

²Museo Nacional de Historia Natural, La Paz, Bolivia.

³Unidad de Ecología Acuática, Instituto de Ecología, Universidad Mayor de San Andrés, La Paz, Bolivia.

⁴Institut de Recherche pour le Development, Montpellier, France.