Ichthyofauna of the upper Juruena river on Chapada dos Parecis , Mato Grosso , Brazil

The fishes herein included were collected in four small streams of the upper rio Tapajós basin. Through fieldwork carried out in 2011, 2013 and 2014 during the low water season 1.728 specimens belonging to 22 species distributed in 11 families, and five orders were captured. Characidae was the most representative family both in number of species and specimens captured. The most abundant species were Hyphessobrycon melanostichos, H. hexastichos, and H. notidanos. Five species are recognized as new, and four as endemic to the upper rio Tapajós basin. This study represents the first fish inventory for the region and will provide valuable information for the conservation of the poorly known diversity of fishes of the Chapada dos Parecis, in the headwaters of the upper rio Tapajós basin.


Introduction
The Neotropical region, that includes the South and part of Central America, harbours the most diverse freshwater fish fauna in the world including 5.400 registered species (Reis 2013), with estimates of a final number between 8.000 -9.000 species (Schaefer 1998, Reis et al. 2016).Most of this ichthyofaunal diversity is located in the Amazon basin (Amazon, Orinoco and Guiana basins), in which 2.354 (Albert et al. 2011) or 2.411 (Reis et al. 2016) valid fish species are included.Most of the major tributaries of the Amazon river basin, still lack an inventory of their fish species, including the rio Tapajós.
Located in the Brazilian Shield the 1.784 km long, rio Tapajós is one of the largest tributaries of rio Amazonas (Costa 2007).Its upper portion was until recently virtually unknown by ichthyologist (Britski & Lima 2008).However, on the last decades, the collecting activity largely increased in the area, 97 of the 109 species presently known from the rio Tapajós basin having been described in the past 30 years.Currently, approximately 300 fishes are registered from the rio Tapajós basin (Ferreira et al. 1998, Camargo et al. 2005, Silva-Oliveira et al. 2016), but collecting efforts have mostly concentrated on the lower and middle portions of the basin, so that a catalogue of fishes of the upper rio Tapajós basin is still lacking.This contribution represents the first attempt to survey the fish species of the upper rio Tapajós basin and will certainly provide valuable information for future studies especially on conservation of the poorly known diversity of fishes of the rio Tapajós basin.

Study Area
The rio Tapajós is formed by the confluence of the Teles Pires and Juruena rivers.The rio Juruena is about 1.240 Km long and is formed by several tributaries draining from the Chapada dos Parecis, an important watershed between three river systems (Madeira, Paraguai and Tapajós river basins) with moderate altitude (750 m), located at the western border of the Brazilian Shield.The rivers in Chapada dos Parecis, tributaries of the rio Juruena (i.e.Mutum, 12 de Outubro, Primavera, Camararezinho, Sacre, Formiga, Juína, Sangue), where samples were obtained for this study, are generally rectilinear, embedded and deep, characterized by turbulent waters and presence of many waterfalls.The studied area is about 500 to 510 meters a.s.l., and is located between Comodoro and Vilhena towns, near BR 364 (Figure 1) on the Chapada dos Parecis and are considered headwater streams entering the upper rio Juruena, rio Tapajós basin.

Sampling
Samples were taken in November 2011, July and August 2013, September and November 2014 in four stations.Sampling took one hour long, and four were undertaken during the day and one during the nocturnal period.The following gears were used: trapezoid hand-nets with area of 1 m 2 and internode distance of 0.1 cm, seine-nets 3-5 m wide, 1.5-2.5 m deep and internode distance of 1 cm and casting-nets 2.5 m deep, 22 m of circumference and internode distance of 1.5 cm.Photographs were taken in three stations that were was georeferenced with a GPS device.Abiotic data such as depth, water transparency and soil were observed in situ.No sazonal differences were detected in the abiotic data.The sampled fishes were anesthetized with clove-oil (1ml/liter), put in plastic bags, fixed in 10% formalin for 48 hours and transferred to 70% ethanol.The material was then counted and identified to the lowest possible level using revisionary studies by Bertaco & Malabarba (2007) 2014), with genera listed in alphabetical order within each family.Voucher specimens were deposited in the fish collections of the Museu de Zoologia da Universidade de São Paulo (MZUSP) and the Universidade Federal de Rondônia, Ictiologia (UFRO-I).Species and specimens were counted for each registered species with data organized in Table 1 and Figures 3 and 4.

Results
The species recorded from the upper rio Tapajós basin are listed in Table 1 and the corresponding photos are provided in Figures 3 and 4. A total of 1.728 specimens representing 22 species distributed in 11 families, and five orders were collected in four stations in both the igarapé Mutum and the igarapé 12 de Outubro.Characiformes (55%, 12 species) was the predominant group, followed by Siluriformes (28%, 6 species), Gymnotiformes (9%, 2 species), Labriformes (4%, 1 species) and Cyprinidontiformes (4%, 1 species) in number of recorded species (Figure 5).
A total of 1.104 specimens belonging to 20 species were recorded from the igarapé Mutum (Stations 1 and 2).The fish fauna is composed by Characiformes (12 species, 913 specimens), Siluriformes (6 species,    (2 species, 11 specimens), Gymnotiformes (1 species, 9 specimens), Labriformes (1 species, 16 specimens) and Cyprinodontiformes (1 species, 3 specimens).The most representative family in number of species and specimens was Characidae, with four recorded species, including the two most abundant species registered in the igarapé 12 de Outubro basin: Hyphessobrycon melanostichos and H. notidanos, with 421 and 99 captured specimens respectively.Nine captured species (43%) were identified as "sp.", including two Characiformes, five (all) Heptapteridae and two (all) Gymnotiformes.Three of the Heptapteridae species, and the two Gymnotiformes species were herein recognized as undescribed species, however more undescribed species herein registered could be recognized in the future with additional research.Moreover, Cetopsorhamdia sp.1, Cetopsorhamdia sp.2 (Heptapteridae), Brachyhypopomus sp.n. and Eigenmannia sp.n.(Gymnotiformes) are currently under taxonomic revisions and preliminary examination indicates that they could represent new species endemic for the rio Juruena (Bockmann pers.communication for Heptapteridae and Ohara.personal observation for Gymnotiformes).Other four species (19%) were tentatively identified indicating that more taxonomic studies on the neotropical ichthyofauna are needed.
No threatened species were found, however four endemic species to the upper rio Tapajós basin were recorded.Melanorivulus modestus, and H. nambiquara are only known from the igarapé Mutum and Hyphessobrycon notidanos is only known from the igarapé 12 de Outubro.Even though Hemigrammus skolioplatus is known from both the igarapé Mutum and the igarapé 12 de Outubro, it occurs only in a small restricted area.
A comparison of the species herein recorded and the fish assemblage from the lower portion of the rio Tapajós basin was performed based on the available literature (Ferreira et al. 1998, Camargo et al. 2005, Silva-Oliveira et al. 2016) and no common species between two portions was observed.The headwater streams seem to harbor a unique species assemblage   due to observed differences in abiotic factors such as temperature, light, hydrologic regime, water chemistry, substrate type, food resources and species pool influenced by small-scale differences in local conditions (Meyer et al. 2007).
A high number of species and specimens were captured in the igarapé Mutum, with the highest values obtained for the survey undertaken in Station 1, and the lowest values in Station 2. On the other hand, a low number of species and specimens were captured in the igarapé 12 de Outubro.Differences on environmental heterogeneity and presence of riparian vegetation were herein registered, however, the number of species and specimens captured should not be compared within this survey due to the non-standardization of the sampling effort in the field trips.
Four endemic species to the upper rio Tapajós basin were herein registered, including Hasemania nambiquara, Hemigrammus skolioplatus Bertaco & Carvalho, 2005, Hyphessobrycon notidanos and Melanorivulus modestus.Although, Hyphessobrycon hexastichos and H. melanostichos have distribution range apparently restricted to the Chapada dos Parecis, they also were collected in the upper rio Guaporé (13º14'43"S 59º54'26"W), rio Madeira basin and in the igarapé Piracolina (12º49'58"S 60º06'34"W), upper rio Machado, rio Madeira basin (cf.Ohara & Lima 2015, Ohara & Marinho 2016, Ohara et al. 2016), respectively.So Hyphessobrycon hexastichos and H. melanostichos are not herein considered as endemic species for the upper rio Tapajós.According to Ohara & Lima (2015) a large number of fish species from the upper rio Juruena are found exclusively in the headwater rivers of the Chapada dos Parecis, which suggests that the area has apparently an endemic ichthyofauna that differs from rest of the rio Tapajós basin, including the rio Teles Pires.
Additionally, as stated by Meyer et al. (2007) fish fauna from headwater streams can make a significant contribution to regional fish diversity.The presence of a high number of endemic fish and at least five new species in a small portion of the upper rio Juruena indicates it as a hotspot area for fish diversity, and as such as having potential priority for conservation measures (Carvalho & Bertaco 2006, Britski & Lima 2008, Ohara & Lima 2015).

Figure 1 .
Figure 1.Map of the study area showing the four stations sampled (indicated by number) from the upper rio Juruena, rio Tapajós basin, Mato Grosso, Brazil.

Figure 5 .
Figure 5. Relative diversity of species among the five orders registered from the upper rio Tapajós basin.

Figure 6 .
Figure 6.Relative abundance of number of species and number of individuals registered in each sample station in the four stations sampled, upper rio Tapajós basin.

Table 1 .
List of species registered in four stations from the upper rio Juruena, rio Tapajós basin, Mato Grosso, Brazil.
N = number of registered specimens.