Fishes from rio Ibirapuitã basin, Environmental Protection Area of Ibirapuitã, Pampa Biome

The fish species herein presented were collected in streams, swamps and rivers of the rio Ibirapuita basin, middle rio Uruguay basin, in the Environmental Protection Area of Ibirapuita. Samplings resulted in 72 species distributed in 51 genera, 21 families, and six orders. This study represents the first fish survey in the EPA of Ibirapuita (Pampa biome).


Introduction
The number of fish species in the rio Uruguay basin is still unclear, but in a recent study Malabarba et al. (2009) estimated 175 described species plus 50 undescribed species (about 20% of that total). The rio Ibirapuitã is one of main tributaries of the rio Ibicuí drainage (the largest drainage of the rio Uruguay basin) and fish inventories are nonexistent. Information about fish diversity from the rio Ibicuí is scarce (Bossemeyer et al. 1985;Copatti et al. 2009;Weis et al. 1983). However, some biological studies about few species have been conducted in this basin (e.g. Behr and Signor 2008;Giora and Fialho 2003;Zardo and Behr 2012).
The Pampa biome is one of the biomes with the lowest percentage of legally protected area, and in Brazil is represented only on the State of Rio Grande do Sul. The Environmental Protection Area (EPA) of Ibirapuitã is a Federal Conservation Unit in the Sustainable Use category, with an area of approximately 317,000 hectares representing the Pampa, distributed in municipalities of Alegrete, Quaraí, Rosário do Sul, and Sant' Ana do Livramento, State of Rio Grande do Sul (Silva 2010). The EPA of Ibirapuitã is located on the international border Brazil-Uruguay, in the West region of the State of Rio Grande do Sul, and its southern limit coincides with the Brazilian international limit. The climate in the region is subtropical characterized by rainy winter and hot summer.
Due to the lack of information about the ichthyofauna of this basin and be a legally protected area, the objective of this study is provide a species inventory, which may eventually support future studies on fish biology and conservation.

Materials and Methods
Specimens were collected using a dip net (40 x 80 cm frame and 1 mm net mesh size), gill nets (20 m x 1.8 m, 2, 3, 4, 5, 6 cm between knots) and seine net (10 m x 2 m, 5 mm between knots), in May 2011, and in August and November 2012. The fishing gear was selected according to the environmental and hydrological conditions of the sampling sites. Nets remained for 12 to 14 h in the water. Fishes were collected under IBAMA (Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis) Abstract: The fish species herein presented were collected in streams, swamps and rivers of the rio Ibirapuitã basin, middle rio Uruguay basin, in the Environmental Protection Area of Ibirapuitã. Samplings resulted in 72 species distributed in 51 genera, 21 families, and six orders. This study represents the first fish survey in the EPA of Ibirapuitã (Pampa biome).  (1999), the predominance of the Characiformes and Siluriformes seems to be a trend for Neotropical rivers.
The absence of Gymnotiformes species in the catches can be due to the characteristics of the studies sites (rocky substrate, water transparent and current, and absence of aquatic vegetation). Copatti et al. (2009) also not captured no gymnotiform species in the rio Jaguari basin, a tributary of rio Ibicuí, and Carlos E. B. Machado (pers. comm.) collected only one species of Gymnotiformes (Brachyhypopomus sp.n.= B. draco Giora, Malabarba and Crampton) in the arroio Taquarembó, tributary of rio Santa Maria, rio Ibicuí basin. According to Giora et al. (2008) Brachyhypopomus draco inhabits river edges, slow-moving creeks, lagoons and flooded areas with muddy or sandy bottom and abundant emergent or floating vegetation, a habitat not found in the rio Ibirapuitã basin.    Hypostomus isbrueckeri Reis, Weber and Malabarba, 1990 Cascudo X 19618 Hypostomus roseopunctatus Reis, Weber and Malabarba, 1990 Cascudo X 19677 Loricariichthys melanocheilus Reis  Most of the collected species occurred both in the river channel and streams, 37 of them occurring only on "river" and eight exclusively on "stream" (Table 2). In the unique sampled flood area ("swamp") only one species of annual fish was collected (Austrolebias periodicus Costa, Rivulidae). This swamp is located about 300 m from rio Ibirapuitã bank, and is relatively well-preserved ( Figure  2C). The species of Austrolebias live in temporary pools and swamps formed during the rainy months (Costa, 2006). Austrolebias periodicus is considered threatened in Brazil (MMA, 2004;Rosa and Lima, 2008). In State of Rio Grande do Sul, the species also is considered threatened in the category "Vulnerable", mainly due to its restricted area of distribution and loss and degradation of its habitat (Reis et al. 2003b).
Five species were provisionally identified given their uncertain taxonomic status or because they represent undescribed species (Astyanax sp., Gymnogeophagus sp., Hypobrycon sp., Phenacorhamdia sp. and Scleronema sp.). On the other hand, results herein obtained indicate that the diversity of fish in the study area is similar to that known for the rio Ibicuí basin.
Astyanax saguazu was described for two tributaries of the middle rio Uruguay basin, in the province of Misiones, Argentina (Casciotta et al. 2003). The presence of this species in the rio Ibirapuitã basin is the first record for Rio Grande do Sul State, Brazil.
In this study two collected species were recognized as long distance migratory fish by Luz-Agostinho et al. (2010), Prochilodus lineatus (Valenciennes) and Pimelodus maculatus Lacépède. Beyond these, two more long distance migratory fish were visually observed downstream to the waterfall of rio Ibirapuitã (ca. 30°26'S 55°41'W): the "dourado" Salminus brasiliensis (Cuvier, 1816) and the "piava" Leporinus obtusidens (Valenciennes, 1837). The specimens of S. brasiliensis (ca. 50 cm of standard length) were observed in June/2012 by Mariano Pairet (FZBRS, pers. comm.) and of L. obtusidens (ca. 40 cm of SL), P. lineatus (35 to 40 cm of SL) and P. maculatus (25 to 30 cm of SL) in November/2012. In State of Rio Grande do Sul, Salminus brasiliensis is considered to be a threatened species in the category "Vulnerable", due to the alteration of habitat mainly by the interruption of migratory routes caused by hydroelectric dams (Reis et al. 2003b). Most of rio Ibirapuitã basin is located within a Federal Conservation Unity, and it is one of the few fluvial systems of the State of Rio Grande do Sul free of hydroelectric dams, therefore only future studies may indicate the importance of the basin for migratory fish.
Based on specimens collected during this inventory, and the species recorded visually and records in scientific collections, the fish richness on the rio Ibirapuitã basin was relatively high when compared to the rio Uruguay basin, comprising 41% (74 species) of the total number of species estimated for that basin. This result reinforces the importance of preservation of the unique conservation unit on the Pampa biome.
In other studies conducted in the tributaries of the rio Ibicuí, a similar number of species was also found: 81 species to the rio Ibicuí-Mirim (Weis et al. 1983), and 53 species to the rio Santa Maria (Bossemeyer et al. 1985). According to Everton Behr (UFSM, pers. comm.) 111 fish species are found in the rio Ibicuí basin along two years of ichthyofauna study. According to that information, the 74 species recorded herein represent about 66% of total species from the basin.