The fish fauna of the Corrientes stream basin , Patos lagoon system , state of Rio Grande do Sul , southern Brazil

Material and Methods Study site The Corrientes stream basin have an area of about 300 km2, and is inserted in two different geomorphologic situations: Crystalline Shield, characterized by high (up to 350 m) and undulating hills with many rock outcrops, and the Coastal Plain, flat and low, with meadows, wetlands and sandy areas. The Corrientes stream is located north of the municipality of Pelotas, bordering the municipality of Turuçu in Rio Grande do Sul state, southern Brazil (Figure 1). It has about 30 km long; its water flow goes from west to east. In this stream, the density distribution of its sources increases dramatically in the portion corresponding to the slope of the Cristalline Shield, reaching altitudes of 230 m. Its drainage network reaches the 4th order in the transition to the plain, forming the lower course of the stream flowing to the Pequena lagoon, draining into the Patos lagoon.


Introduction
The Neotropical region presents a high diversity of freshwater fish species (Lowe-McConnell 1999) and estimates indicates 3000-5000 species in Brazil (Menezes 1996;Reis et al. 2003;Buckup et al. 2007).Although there is a wide variation in estimates, Brazil has the highest richness of freshwater species of fish in the world.
In a review, Malabarba (1989) found 106 freshwater fish species described or related to Patos-Mirim lagoon basin and Jacuí River, in Rio Grande do Sul State.In a recent study, Malabarba et al. (2009) mentioned 125 described species to this system, and the necessity of describe another 35 species.Subsequent studies included species which occurrence was known in other hydrographic systems, as Acestrorhynchus pantaneiro (Saccol-Pereira et al. 2006), Pachyurus bonariensis (Dufech and Fialho 2007) and Jenynsia onca (Lanés et al. 2008).Besides these species, several other fish species of commercial interest have been introduced into natural environments due to pisciculture activity, as occurred in the estuary of Patos lagoon (Garcia et al. 2004), Caí River (Dala-Corte et al. 2009) and in the Sinos River (Leal et al. 2009).
Despite the high species richness of the Patos lagoon system, there are few studies of fish assemblages in coastal water bodies, mainly in the southern of Rio Grande do Sul state (Garcia et al. 2006).Most of the studies in this area were developed in independent drainages that flow directly into the sea (Tagliani 1994;Loebmann and Vieira 2005).Although being located in the same ecoregion (Abell et al. 2008), these drainages do not belong to Patos lagoon system.Knowledge of fish fauna composition of an environment is fundamental to future studies involving management and conservation.Thus, this work is aimed to provide the list of fish species of Corrientes stream, southern Rio Grande do Sul state, Brazil.

Abstract:
The fish sampled in this study were captured in seasonal collections samplings, conducted between May 2006 and February 2007 in 15 stretches of the Corrientes stream basin, Patos lagoon system, Rio Grande do Sul state, Brazil.A total of 8088 specimens were collected, belonging to nine orders, 24 families and 68 species.In general, the ichthyofauna in this basin has the same pattern recognized for Neotropical rivers with predominance of Characiformes and Siluriformes orders and a high representative of the Characidae and Loricariidae families.
It was observed a larger representation of the family Characidae, with 20 species and 47 % of the individuals captured, followed by Loricariidae, with eight species and representing 22 % of fishes sampled.The highest richness for the family Characidae recorded in this study, was also observed in other basins of the Patos lagoon system (Garcia et al. 2006;Petry and Schulz 2006;Leal et al. 2009).According to Mathews (1998), the number of families represented is relatively large in places with high richness, and few families have most of the species.
The record of 68 species of fishes in the Corrientes stream basin is in accordance with other studies conducted in the state of Rio Grande do Sul: Tagliani (1994) reported the occurrence of 31 species in three streams of the coastal plain of Rio Grande do Sul; in the National Park of Lagoa do peixe, 73 species were recorded (Loebmann and Vieira 2005); in the Ecological Station of Taim, Garcia et al. (2006) identified 62 species of fishes, while in the Sinos River basin, Petry and Schulz (2006) captured 63 species.In a recent study, Leal et al. (2009) expanded the richness of the Sinos River, totaling 102 species.In Caí River basin, Dala-Corte et al. (2009) reported the occurrence of 20 species.In the estuary of Patos Lagoon, which has a large volume of water and is connected with Camaquã, Jacuí, Caí, Sinos, Gravataí River basins and the Mirim lagoon complex, the richness is of 110 species (Garcia and Vieira, 2001).Moreover, in adjacent drainages of Uruguay River, Copatti et al. (2009) recorded 26 species on Jaguari River basin and Azevedo et al. (2003) sampled 27 species in the Felizardo stream.
The most abundant species were respectively Hyphessobrycon luetkenii, Rineloricaria cadeae, Bryconamericus iheringii and Phalloceros caudimaculatus, totaling about 55 % of the specimens captured.The high abundance of H. luetkenii was also observed by Tagliani (1994) and, according to the author, this characid was one of the most abundant species in the sampled streams, but has shown seasonal variation in abundance throughout the sampling period.Five species had only one specimen captured: Atherinella brasiliensis, Brachyhypopomus bombilla, Oligosarcus sp. and Paralichthys orbignyanus.
Among the species caught, Trachelyopterus lucenai is considered invasive to the Patos lagoon system (Bertoletti et al. 1992;Buckup et al. 2007).This species is commonly recorded in the system, and their populations are already considered stabilized (Becker 2001).The composition of the ichthyofauna found in the Corrientes stream is typical of this type of aquatic environment and most of the species commonly occur in the Patos lagoon system (Malabarba 1989;2008;Reis et al. 2003;Buckup et al. 2007).

Figure 1 .
Figure 1.Image of sample sites in the Corrientes stream Basin, Patos lagoon system, Brazil.

Table 1 .
Geographical coordinates and altitude of the 15 stretches sampled in the basin of the Corrientes stream, Patos lagoon system, Rio Grande do Sul state.

Table 2 .
Fish fauna caught at each sample site in the Corrientes stream basin, Patos lagoon system, Rio Grande do Sul state, from May 2007 to February 2008.