Acta Biológica Colombiana

The genus Synbranchus Bloch, 1795 is endemic to Central and South America and is characterized by being very specialized in many aspects, including the anatomical, physiological, and behavioral (Rosen and Greenwood, 1976). Currently, it contains three recognized species (Rosen and Greenwood, 1976; Favorito et al., 2005). Synbranchus marmoratus Bloch, 1795, popularly known as the marbled or creole swamp eel, is the only species found in Argentina (Liotta, 2005). It prefers freshwater habitats and lives in muddy areas, riverbanks, streams, and lagoons. It can grow to be approximately 1000 mm long, with body scales. Rayless dorsal and anal fins; represented by long skin folds. No paired fins except for membranous larval pectoral fins (Ringuelet, 1975). It's characterized by having gills reduced to a single branchial membrane and by being able to breathe air through oropharyngeal breathing. It lacks an air bladder and can leave the water and move along the ground until it finds another water body (Fernández, 2018).

Liotta (2005) defined the distribution of this species in Argentina without completing an exhaustive revision of the bibliography, as then it was impossible to obtain old articles that had been published in foreign journals without free or unrestricted access. On the other hand, although the International Union for the Conservation of Nature [IUCN] considers the conservation status of S. marmoratus as "Least Concern", given that it has a wide distribution in Central and South America (Daniels and Maiz-Tome, 2019), we believe that each country where the species is distributed should carry out its own evaluation of the status of conservation.

Therefore, the objective this study is to provide a new latitudinal and altitudinal record that widens the distribution of the species at its most western point towards Argentina's Central Andes in the Calingasta Department of the San Juan Province. Additionally, this new record is at least 300 meters higher than previous records of the species, whose altitudinal range observed in the Colombian and Ecuadorian Andes is above 10 masl and below 1000 masl (Maldonado-Ocampo et al., 2005; Rodríguez-Galarza et al., 2017). Finally, we update the distribution map for S. marmoratus in Argentina based on this record and a complete review of the literature, to generate base information that serves for a future categorization of the conservation status in the country.

On September 12, 2016, during an ichthyofaunal survey of mountain rivers in the Calingasta Department of San Juan Province, Argentina, we placed tuna as bait in a double cone fish trap for an entire day along the floodplain at the southern edge of the Agua Negra Stream (31°15' S, and 69°25' W, 1330 m. a. s. l.). This body of water's origin is subterranean, and it is the last tributary of the Castano River before it joins the Los Patos River, which later forms the San Juan River downstream. In the trap, we captured an individual of Synbranchus marmoratus (Fig. 1).

Figure 1.: (a) Specimen of Synbranchus marmoratus found in Calingasta Department. (b) Detail of the dorsal view of the fish, showing the coloration pattern of the live specimen. (c) Detail of the ventral view of the fish, showing the coloration pattern of the live specimen.

In addition, we carried out a specific bibliographic search of the keywords "Synbranchus marmoratus" + "Marbled swamp eel" + "Argentina" in Google Scholar. This search turned up 58 papers, for which we obtained data related to geographical distribution whenever possible. With this information, we created a map of the new distribution of S. marmoratus in Argentina, based on that of Liotta (2005) together with the ecoregions of freshwater fish found in the country, as described by Abell et al. (2008). Furthermore, we have provided a table with information on the new points of distribution.

Based on the new record and points of distribution obtained for S. marmoratus through the literature, we have created an updated map with the current distribution of the species in Argentina (Fig. 2). Likewise, in Table 1, we include information on its new locations. The new location of S. marmoratus (Fig. 1) in the Province of San Juan is highly relevant since it corresponds to the most western point of its current distribution known in Argentina (Fig. 2). This new record also widens the distribution of the species in the Province of San Juan approximately 90 to 120 km in a straight line from previous records, which are mentioned for 9 de Julio, 25 de Mayo and Zonda Departments (Murúa and Acosta, 1997; Gómez, 2001; Acosta et al., 2016). Though all the records until now have been found in the San Juan River basin, we must highlight the fact that the new location is found in the Calingasta Valley, between the Andes and the Pre-Andes foothills, while the other records were found east of the Pre-Andes in plains and valleys at lower elevations and in different environments.

Figure 2.: Map of the current distribution of Synbranchus marmoratus based on data obtained from Liotta (2005) and using the Freshwater Ecoregions of the World (sensu Abell et al., 2008) as an ecological unit. (a) Records from the previous study of Liotta (2005) and the updated records. (b) The new records for the Province of San Juan are shown.

Table 1.: Details of the newly updated records of the distribution of Synbranchus marmoratus in Argentina.

This finding is interesting from a biogeographical point of view, as Ringuelet (1975) considers S. marmoratus to be an indicator of the ichthyofauna of the Great River and Pampa Biogeographical Provinces (López et al., 2008), while the ichthyofauna of the Province of San Juan belongs to the Andean Cuyo Province, whose indicator species include Hatcheria macrae, Olivaichthys (Diplomystes) cyuanus and Percichthys trucha (López et al., 2008). Even though these Biogeographical Provinces share S. marmoratus, Ringuelet (1975) believes that the border between the ichthyological territories is determined by an ecological barrier and not by hydrographic basins or physiographic barriers. In this way, we provide a new record latitudinal and altitudinal that allows us to extend the western distribution limit of the species in the country to the Central Andes of Argentina and contribute to the knowledge of the southernmost distribution of this species widely distributed in Central and South America.