Fish fauna from Río Pilcomayo National Park and Ramsar Site and its surroundings, Formosa, Argentina

The first list of fish species from the Rio Pilcomayo National Park and Ramsar Site (RPNP), located in the Wet Chaco plains of northern Argentina is presented here. Samplings were carried out bimonthly from December 2006 to January 2008 in sites representative of the different landscapes, in both dry and wet seasons. A total of 77 species were collected, belonging to 23 families and eight orders and covering 54% of the province ichthyofauna. New records to the Province of Formosa are Brachyhypopomus gauderio Giora & Malabarba, 2009; Cyanocharax sp. and Hypophthalmus edentatus Spix & Agassiz, 1829.


Introduction
The northeastern corner of Formosa province belongs to the wet plains of the Great Chaco region, whose fish fauna is well known for their particular adaptations to seasonal environments (Carter and Beadle 1931). Its ichthyological composition was summarized by Menni (2004), but none of the previous studies has taken into account differences in landscape structure and seasonality. The main objective of this paper is to document the fish fauna of the Río Pilcomayo National Park and Ramsar Site, based on year round inventories which involved different landscape patterns and hydrological conditions.

Study Area
The Río Pilcomayo National Park and Ramsar Site (RPNP) is located in the northeastern corner of Formosa province, northern Argentina (Figure 1), comprising 55,000 ha in the Wet Chaco ecoregion (Burkart et al. 1999;Abell et al. 2008) and in the Great Rivers Province . The RPNP area comprises a mosaic of different wetland types of fluvial origin within the Lower Pilcomayo River basin. All wetland types are connected by local flooding of the Lower Pilcomayo or by surface runoff during the rainy season, most aquatic environments are isolated or even dry out during the dry season (Bucher and Chani 1998).

Wetland landscapes
Six different landscapes representative of the wetland environments of the RPNP and its neighbouring areas were identified by means of satellite image interpretation, and checked in the field (Figure 2). swamp areas. Laguna Blanca lake presents turbid waters due to the northern winds.
Outside the National Park, land is subject to different uses: urban, annual crops (cotton), fruit orchards (grapefruit and bananas), and cattle ranching. We sampled water bodies 1-2 km outside the Park boundary which correspond to the following landscapes: Riacho Porteño (L4): This small river is a tributary of the Lower Pilcomayo River, which joins just before reaching the Paraguay River. It drains the main agricultural area and its channeled hydrology is heavily modified by the presence of weirs and locks to retain water during the dry season, and ditches to drain excess water to nearby swamps in the wet season. Most gallery forests have been replaced by crops that are cultivated organically.
Grazed swamps (L5): Landscapes outside the National Park from the city of Laguna Blanca are usually palm savannas they are heavily grazed throughout the year. The swamp Estero Sastrow is located between the west margin of the Riacho Porteño and the National Park, receives urban and highway rainwater drainages and is fragmented in half by Provincial Highway 86. Estero Balcalda is located near the easternmost corner of the National Park; it presents small dirt weirs to retain water when the dry season starts. Fires during the spring season are frequent and are set up by ranchers.
Urban ditches and ponds (L6): In the city of Laguna Blanca there is an extensive network of manmade ditches and open water bodies which could offer habitat to many species. Large ponds resulting from road construction are used to collect rainwater for municipal use while shallow ditches drain rainwater to nearby swamps and wet prairies.

Seasonality
Fish species were additionally grouped based on their temporal occurrences taking into account wet and dry seasons. Permanent species (P) were present all year round. Semi permanent ones (S) showed in both seasons but not in all sampling surveys. Seasonal species were present on either wet (W) or dry (D) periods. We labeled as occasional (O) the remaining species, which appeared with single individuals in one or two sites in a single sampling field trip.
From the total amount of fishes collected in the National Park and surrounded areas, all orders and families were represented inside the RPNP. However, only five orders and 16 families were found outside. In terms of richness representation at the species level, both inside and outside the National Park areas show high values for the landscapes characterized, the RPNP showed 84% of the species records while outside landscapes contributed with 68%. There are no man-made landscapes inside the Río Pilcomayo National Park.
Potamotrygon motoro (Müller & Henle, 1841) were only found in the Pilcomayo River. Lepidosiren paradoxa Fitzinger, 1837 were only captured in Laguna Blanca lake, although was considered a common species by locals. In terms of exclusiveness at the species Tridentopsis cahuali Azpelicueta, 1990 were only found in swamps inside the RPNP and Rhamphichthys hahni (Meinken, 1937) in Laguna Blanca lake.

Discussion
Considering the available references for the Pilcomayo River basin (Ringuelet et al. 1967;Menni et al. 1992, Baud et al. 1993Mandelburger et al. 1996), a total of 159 species have been previously registered with the study area representing around 50% of the total species recorded in the basin. Menni (2004) mentioned the presence of 143 fish species in the Formosa Province, based on point records mostly from large rivers and related wetlands while Canón Verón (2008) reported 89 species just for the eastern portion of the province. Considering these references together, the RPNP area covered 54% of the ichthyofauna known from this province.
Our study provided new records for the RPNP area. Five species were added to Formosa's ichthyofauna: Astyanax pelegrini Eigenmann, 1907 andT. pantanensis (see Brancolini et al. 2011), Cyanocharax sp., Hypophthalmus edentatus, andBrachyhypopomus gauderio. In addition, this study presents the first species list of fishes from the Río Pilcomayo National Park and Ramsar Site organized by taxonomy and by landscape characterization, with coded information on their temporal occurrence. Our sampling design, which included the variety of aquatic environments present in the different landscapes, both in the National Park and its surroundings and their seasonality allow our results to be a useful reference as a baseline for ecological, conservation and environmental impact studies.