Fishes of Alto Jacuí sub-basin : a poorly studied sub-basin of northwestern Rio Grande do Sul , Brazil

The streams in the state of Rio Grande do Sul (mainly in the Alto Jacuí sub-basin belonging to the Laguna dos Patos system) have scarce information about their ichthyofauna. Thereby for providing information about stream species, the purpose of the present study was to inventory the ichthyofauna of the streams of the Alto Jacuí sub-basin, located in northwestern state of Rio Grande do Sul. The samples were taken bimonthly from June 2012 to June 2013 using electrofishing technique in 10 streams. A total of 13,247 specimens were collected belonging to 42 species, 10 families and six orders. We report the occurrence of five new species that have not yet been described by researchers.


INTRODUCTION
Fish are considered the most diverse group of vertebrates (Lowe-MacConnell 1999), with an estimated richness of 32,900 species (Froese and Pauly 2014).By December 2013, Pelayo-Villamil et al. (2014) had found 14,782 described species of fish that occur only in freshwater.Although there is a lack of a complementary information, current estimates of the icthyofauna in the Neotropical region are that there are about 6,000 to 8,000 species, totaling 13% of the vertebrate biodiversity in aquatic ecosystems worldwide, with Brazilian continental waters showing 21% of global diversity (Reis et al. 2003;Agostinho et al. 2005).
There is still a lack of knowledge of fish richness, mainly in South America, Africa and Asia, whichis due to a lack of sampling and databasingPelayo- Villamil et al. 2014).Brazil has the largest river networks in the world (Galves et al. 2009); however, many Brazilian basins and sub-basins have not yet been sampled (Agostinho et al. 2005), or there exists little information about their fish fauna, especially with medium-sized and small water bodies such as streams (Castro 1999).According to Langeani et al. (2007) streams are the environments that have the highest number of new species still to be discovered.But the small size of streams and headwater environments makes these places more susceptible to anthropogenic action and they may experience significant change in their population structure, leading to the disappearance of the most sensitive species (Galves et al. 2009).This situation makes it difficult to understand ecological, biological and biogeographical processes (Barletta et al. 2010).
Little information are available about sampling and studies of the ichthyofauna in streams for the Jacuí river basin and no studies of the upper region of the basin, called the Alto Jacuí sub-basin.Malabarba (1989) showed a list of freshwater fish present in the Laguna dos Patos system and cited species found in Jacuí River and its tributaries.Alves and Fontoura (2009) identified the distributive pattern of migratory fish of the Jacuí River basin, but the data were obtained through interviews, collections, literature and technical studies (EIA-RIMA Bonato and Fialho | Fishes of Alto Jacuí sub-basin Subtropical Ombrophilous Forest.The economy is based on agriculture (soybeans, corn, wheat and rice) and livestock.The basin is drained by the Jacuí, Jacuí-Mirim, Jacuizinho, Caixões, Ivaí and Soturno rivers (SEMA 2010).The Jacuí River is the main tributary of the basin and it is responsible for 85% of the waters forming the Lago Guaíba (FEPAM 2011).
Thus, this study was conducted in 10 streams (Figures 1 and 2-11) in northwestern Rio Grande do Sul, which corresponds to the Alto Jacuí sub-basin (Table 1).All streams flow into the Jacuí River, which is one of the main tributaries to the Laguna dos Patos system.

Data collection
Fish samples were collected with authorization number 34940 from register number 3196382 from Instituto Chico Mendes de Conservação da Bio diversidade (ICMBio).This study was approved by the Ethics Committee on Animal Use of the Universidade Federal do Rio Grande do Sul (permit number 24434) and was conducted in accordance with protocols in their ethical and methodological aspects for the use of fish.
The fish were collected in June, August, October and December 2012; February, April and June 2013.Each sampling event lasted four days.For the sampling, we used electrofishing with three stages of 30 min each, in stretches of 50 m per sampling stream.After sampling, fish were euthanized with 10% eugenol (Vidal et al. 2008;Lucena et al. 2013a), fixed in 10% formalin Estudo e Relatório de Impacto Ambiental) developed in the study region.Additionally there are some taxonomic reviews and descriptions of new species that are distributed on this drainage (Ottoni and Cheffe 2009;Menezes and Ribeiro 2010;Carvalho and Reis 2011).
We emphasize that to understand the ecological mechanisms in these little-explored environments we must use many tools, including ichthyofaunal studies.Streams are highly heterogeneous environments (Winemiller et al. 2008) and this allows for the establishment of numerous species of fish.Further, more studies of streams in south Brazil are necessary because some basins are not as well explored as the Alto Jacuí sub-basin.Therefore, the aim of this study is to inventory and provide more information about distribution and species richness of ichthyofauna in the Alto Jacuí sub-basin located in northwestern Rio Grande do Sul.

Study site
The Alto Jacuí sub-basin belongs to the large Laguna dos Patos system and is located in the state of Rio Grande do Sul in the northwestern Middle Plateau and Central Depression region.The Alto Jacuí has its headwaters located in the municipality of Passo Fundo and occupies an area of 16,062 km 2 with its rivers flowing into the Lago Guaíba (COAJU 2009).The basin's vegetation consists of Seasonal Deciduous Forest and some areas of  Table 1.Bonato and Fialho | Fishes of Alto Jacuí sub-basin Lucena (2010), Ferrer and Malabarba (2013), Lucena et al. (2013b), Lucena and Soares (2016) and additional literature cited herein.Classification and nomenclature follows Reis et al. (2003), with additional changes made by Thomaz et al. (2015) for Characidae.The nomenclature for Cichlidae followed the new classification of bony fishes proposed by Betancur et al. (2013) that include this family in the order Cichliformes.The voucher specimens were deposited in the fish collection of the Departamento de Zoologia at Universidade Federal do Rio Grande do Sul (UFRGS; Table 2).
Five species are identified only to genus level and correspond to undescribed species: Australoheros sp.(Rícan and Kullander 2008), Bryconamericus sp.b (Silva 1998), Heptapterus sp.(Bockmann 1998), Ituglanis sp.(J.Ferrer, personal communication) and Bryconamericus sp. a which also seem to be a new species but, could not be described because it may just be a variation (as color and body shape) of Bryconamericus iheringii.According to Bonato and Ferrer (2013), the individuals of Phalloceros spiloura Lucinda, 2008 collected in the Alto Jacuí subbasin during the present study represent the first record of this species to the Laguna dos Patos system.
The highest species richness was found in RP, RT, RC and RQ with 28 species, 27 species, 25 species and 21 species, respectively.RM and RSC showed the lowest species richness with only 15 and 14 sample species.

DISCUSSION
According to Pelayo-Villamil et al. (2014) an average of 240.2 species of fishes were described per year in the last ten years worldwide.The five new species uncovered by this inventory (Australoheros sp., Heptapterus sp., Bryconamericus sp. a and b, and Ituglanis sp.) support the importance of this type of study.In addition, inventories are important in extending the distributional range of some species, such as Phalloceros spiloura that was previously only known from the coastal drainages of states of Rio Grande do Sul and Santa Catarina, Iguaçu and Uruguay river basins, and as part of this study, was found in the Alto Jacuí sub-basin representing a new record for the Laguna dos Patos system (Bonato and Ferrer 2013).Malabarba (1989) registred 25 species of the 42 species sampled in this study to Laguna dos Patos system.The most recent literature indicates a total of 160 species to the Laguna dos Patos system (Malabarba et al. 2009) including 35 species that were new species and yet not described in 2009.Of these 35 species listed by Malabarba et al. (2009), we have sampled five species that were described in recent years (Oligosarcus jacuiensis Menezes & Ribeiro, 2010;Hisonotus brunneus Carvalho & Reis, 2011; Astyanax procerus Lucena, Castro & Bertaco, 2013;Astyanax xiru Lucena, Castro & Bertaco, 2013;Trychomycterus poikilos Ferrer & Malabarba, 2013), indicating that a representative amount of the ichthyofauna of the upper Jacuí River was described in recent years.There are no comparable studies for the Alto Jacuí sub-basin.We can only make comparisons with other basins belonging to the Laguna dos Patos system.For stream environments Bozzeti and Schulz (2004) found 57 species in the Gravataí and Sinos subbasins, Hirschmann (2009) found 55 species in the Forqueta sub-basin (Taquari-Antas basin), and Becker et al. (2013) found 119 species for the Taquari-Antas basin but in respect to the last study, the high number of captured species is likely due to their larger sampling of 519 sites.
The number of species found in this study is lower compared to those cited by other studies mainly because it was conducted in streams from a headwater region and many of the streams (of lower species richness) are first-order.The highest occurrence of the orders Characiformes, Cichliformes and Siluriformes in studies is also well documented for the Laguna dos Patos system and for the Neotropical region (Castro 1999;Garcia et al. 2003;Buckup et al. 2007;Lévêque et al. 2008;Costa and Schulz 2010).Headwater streams do not have an exclusive fish fauna but, species that form populations residing in streams and also that occur in larger bodies of water with different characteristics (Castro 1999).The fish fauna of streams is based on small species and according to Castro (1999) it seems to be the only general pattern with real diagnostic value for stream environments.In this study, the streams with lower species richness are the first-order streams, which have a habitat of lower complexity as RD, RV and AA streams (see Table 1 for stream codes).This situation is expected in accordance with the River Continuum Theory (Vannote et al. 1980).Thus, the larger streams, with greater width between banks, areas with and without shading, and more heterogeneous environment showed the highest species richness (Fereira and Casatti 2006;Súarez and Petrere-Junior 2005) as occurred in the RT, RP and RC streams.
Despite the fact that we did not evaluate the degree of anthropic influences in the sampled streams, all streams sampled here showed some kind of human interference.Most streams are very close to agricultural areas with the presence of dairy cattle or pig livestock.In stream RP there was a considerable amount of waste coming from homes and sometimes we found dead animals within the stream.Probably the residents of the region slaughter animals for their own consumption and discard the remains of the animal in the river.However, this stream had considerable marginal vegetation and a heterogeneous environment with changing pools and areas of rapids, which led to the high amount of richness observed.
Due to a lack of data for streams of the studied subbasin it is difficult to say that the number of species found is representative of the streams belonging to Laguna dos Patos system.The checklist showed 42 species representing 26% of the species mentioned for the Laguna dos Patos system.This study is an important record for the region of the Alto Jacuí sub-basin due to the lack of extensive collecting effort in the region.The expansion of the sampled streams in Jacuí River basin may increase the records of species and information about endemic species.the species figures; the Orlandi and Bonato families for help and support in field work; and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Proc.1104786, to KOB) for financial support.We also thank to Adam J. Taylor for reviewing the English of this manuscript.

Figure 1 .
Figure1.Sampling streams in the Alto Jacuí sub-basin.For stream code see Table1.

Table 1 .Table 1 .
Geographic coordinates, elevation and localization of the sampled streams and their respective codes in the Alto Jacuí sub-basin.Bonato and Fialho | Fishes of Alto Jacuí sub-basin Rodriguez and Reis (2008)0% alcohol for conservation.The taxonomic identification was carried out in the laboratory usingRodriguez and Reis (2008),Bertaco and

Table 2 .
List of fish species collected at each sampled stream in the Alto Jacuí sub-basin.See Table1for stream names.Asterisk indicates the endemic species to Laguna dos Patos system.