Tocantins Basin Research Articles

IMPACTS OF THE HYDROELECTRIC POWER GENERATION OVER THE FISH FAUNA OF THE TOCANTINS RIVER, BRAZIL: MARABÁ DAM, THE FINAL BLOW

As the eyes of environmentalist's focused on the Madeira, Xingu and Tapajos rivers dams, one unknown project to bystanders will negatively affect an entire watershed, causing impacts far greater than any other megadam constructed in Brazil. Despite the environmental modifications, little is known about the UHE Maraba dam and its impacts over such a splendid cellar of species: the Araguaia- Tocantins basin. Historically the Tocantins River is the most impacted amazon tributary, with several already built dams, though the Araguaia River is free of dams. Building the UHE Maraba dam will affect both rivers, and probably extinguish many species increasing the already high number of Amazonian endangered fish species. Due to its unique evolutionary history among Amazonian tributaries, the endemicity found in the basin is probably higher than any other amazon tributary, inasmuch as some authors consider it as a different watershed, separated from the Amazon. Describing and foreseen the impacts locally and globally are the main goals of the present study.As the eyes of environmentalists and researchers focused on the Madeira, Xingu and Tapajos rivers dams, one unknown project to bystanders will negatively affect an entire watershed, causing impacts far greater than any other megadam constructed in Brazil. Despite the environmental modifications, little is known about the UHE Maraba dam and its impacts over such a splendid cellar of species: the Araguaia- Tocantins basin. Historically the Tocantins River is the most impacted amazon tributary, with several already built dams, though the Araguaia River is free of dams. Building the UHE Maraba dam will affect both rivers, and probably extinguish many species increasing the already high number of Amazonian endangered fish species. Due to its unique evolutionary history among Amazonian tributaries, the endemicity found in the basin is probably higher than any other Amazon tributary, as some authors consider it as a different watershed, separated from the Amazon. Describing and foreseeing the impacts locally and globally are the main goals of the present study.

Two new species of Curculionichthys (Siluriformes: Loricariidae) from the rio Amazonas basin, Brazil.

In the present study, we describe two new species of Curculionichthys from rio Tapajós and rio Tocantins basins in Brazil. Both species present all diagnostic features of Curculionichthys. Furthermore, both species C. tukana and C. itaim are distinguished from congeners by the combination of seven characters: (1) a higher number of plates in abdominal lateral plates series; (2) the absence of large conspicuous odontodes forming rows on head and trunk; (3) the anterior profile of the head pointed; (4) a higher number of dentary teeth; (5) the lack of contrasting dark spots at the anterodorsal region of body; (6) the absence of an irregular concentration of chromatophores that entirely cover the anal-fin origin and adjacent region, and distal portion of the first unbranched anal-fin ray; and (7) the presence of odontodes forming aligned rows, more evident in the dorsal portion of head and in the lateral portion of caudal peduncle. Furthermore, C. tukana can be further distinguished from congeners by three characters: (1) the papillae aligned in series that extends from the distal portion of lower lip to dentary; (2) the absence of dark-brown spots scattered over the body; and (3) a higher number of maxillary teeth. The species C. itaim also can be further distinguished from congeners by five characters: (1) the papillae randomly distributed throughout the lower lip; (2) a smaller number of medial plates series on lateral portion of the body following the lateral line; (3) a smaller number of median plates series in abdomen; (4) the absence of dark-brown spots scattered over the body; and (5) the absence of one unpaired platelet on the dorsal portion of the caudal peduncle.

Evolution in action: allopatry, variable diversity and a stepping-stone model of migration among populations of the freshwater bivalve Triplodon corrugatus from the north-eastern Amazon

Triplodon corrugatus is a freshwater bivalve (Hyriidae) endemic to the Amazon, Orinoco and Tocantins basins, and the Piria river. Our understanding of hyriid diversity at, and below, the species level, remains poor. The genetic diversity of T. corrugatus from the Tapajos, Amazon, Tocantins, Irituia and Piria rivers in the north-eastern Brazilian Amazon was investigated. Except for the Irituia, where a single COII–COI haplotype had been fixed, all the other populations had medium to high haplotype diversities, and all populations had low nucleotide diversities. Pairwise fixation indices indicated that all populations were structured, except for comparisons between the Tapajos and Amazon, and the Amazon and Tocantins rivers, which may be explained by a stepping-stone model of migration. AMOVA detected that 81.28% of the variation was among populations. However, STRUCTURE analyses corroborated only the Piria river specimens as comprising a distinct population, which is being maintained by allopatry due to the current isolation between the Piria, and the Amazon and Tocantins basins.

Description of a new species of Gymnotocinclus from the rio Tocantins basin with phylogenetic analysis of the subfamily Hypoptopomatinae (Siluriformes: Loricariidae).

Gymnotocinclus canoeiro n. sp. of the Hypoptopomatinae is described from small tributaries of the upper rio Tocantins basin. It is distinguished from G. anosteos by having five characters: (1) the presence of body dermal plates, (2) the pectoral girdle not exposed in ventral view, (3) the pelvic spine longer than pectoral spine in males, (4) the pectoral fin with seven to eight branched rays, and (5) the presence of an adipose fin. Furthermore, maximum likelihood (ML) analysis was used to estimate a molecular phylogeny from previously published data of one nuclear (F-Reticulon 4) and three mitochondrial (16S RNA, COI and CytB) genes. The phylogenetic results revealed the new species as a sister taxon of Gymnotocinclus anosteos within the Otothyrini. We also included samples of Nannoplecostomus eleonorae that appeared sister group to all other Neoplecostomini species, and Plesioptopoma curvidens that appeared within the Neoplecostomini forming a sister clade to all species of Neoplecostomus, except N. ribeirensis and the species of Pareiorhina, except P. rudolphi.

A new genus of Anostomidae (Ostariophysi: Characiformes): Diversity, phylogeny and biogeography based on cytogenetic, molecular and morphological data

A new genus of Anostomidae (Characiformes) is described to include ten valid extant species previously classified in Leporinus or Hypomasticus and distributed throughout most major river basins in South America: L. brinco, L. conirostris, L. elongatus, H. garmani, L. macrocephalus, L. muyscorum, L. obtusidens, L. piavussu, L. reinhardti, and L. trifasciatus. The monophyly of Megaleporinus is well-supported in a phylogenetic analysis based on two mitochondrial and three nuclear genes, as well as its sister group relationship to Abramites. Megaleporinus is diagnosed by having the exclusive combination of three unicuspid teeth on each premaxillary and dentary bone and a color pattern composed of one to four dark midlateral blotches. Additional distinguishing features and possible synapomorphies include a unique ZZ/ZW sex chromosome system confirmed for six congeners and a drumming apparatus wherein the first rib is elongated and associated with hypertrophied intercostal muscles, which was confirmed for three congeners as exclusive to mature males. Furthermore, our study identified at least four undescribed cryptic species, emphasizing the need for further taxonomic work and genetic analyses. A time-calibrated phylogenetic and biogeographical analysis of the new genus suggests that speciation in the proto-Amazon-Orinoco lineage was primarily driven by paleogeographic processes, such as the formation of the Orinoco and Tocantins basins. Dispersal and diversification of the genus in coastal basins draining the Eastern Brazilian Shield appears to have been facilitated by connections between paleo-basins during low sea level periods and headwater captures between coastal and inland watersheds. The present contribution demonstrates the importance of integrating data from morphology, DNA sequences and cytogenetics to advance the taxonomy and systematics of any complex species group.

Redescription ofMicrosternarchus bilineatus(Fernández-Yépez, 1968) (Gymnotiformes: Hypopomidae, Microsternarchini), with the designation of a neotype

ABSTRACT. Microsternarchus bilineatus Fernandez-Yepez, 1968 is a small, inconspicuous electric fish distributed in the Orinoco, Amazon and Tocantins basins. Its holotype and paratypes from Rio San Jose, a tributary of Rio Guariquito, Orinoco basin, Venezuela, are apparently lost. We examined 14 specimens collected in Rio San Bartolo, also a tributary of Rio Guariquito, 110 km by river from Rio San Jose. Because of its proximity to the type locality and apparent conformity to the original description, we used these newly collected specimens to redescribe M. bilineatus using external morphology, morphometrics, meristics, and osteology including high-resolution X-ray computed tomography. In order to address geographic variation we compared Rio San Bartolo specimens with others of, or close to, M. bilineatus from Casiquiare river and from two streams in Roraima state, Brazil. In our analysis specimens from distant localities differ in the interobital distance and mouth size, number of anal-fin rays and skelet...

A new species of Ituglanis (Siluriformes: Trichomycteridae) from the Tocantins and Paranaíba river basins, central Brazil, with remarks on the systematics of the genus.

Ituglanis goya, new species, is described from the Paranaíba and Tocantins river drainages, central Brazil. This is the first species of the genus described for the Upper Paraná system and the second epigean Ituglanis for the Tocantins basin. The new species is distinguished from its congeners by the combination of a color pattern formed by longitudinal stripes and spots, absence of the anterior cranial fontanel, pattern of the cephalic laterosensory system and several fin-ray counts. Ituglanis goya exhibits morphological features that oppose the traditional hypotheses of alignment of the genus with the TSVSG clade of Trichomycteridae. These and other issues concerning the systematics of Ituglanis and the Trichomycterinae are critically discussed.

Potamotrygon rex, a new species of Neotropical freshwater stingray(Chondrichthyes: Potamotrygonidae) from the middle and upper rio Tocantins, Brazil, closely allied to Potamotrygon henlei (Castelnau, 1855).

A systematic revision of the rio Tocantins stingrays has confirmed the occurrence of a new species of Potamotrygon first discovered more than two decades ago but which lacked material for a thorough description. Field surveys since undertaken in the middle and upper rio Tocantins have assembled significant material that forms the basis of an ongoing revision of the diverse Tocantins potamotrygonid assemblage. Potamotrygon rex, sp. nov., is a very large, "black stingray" species from the mid and upper rio Tocantins that is closely related to P. henlei (Castelnau), which occurs in the lower Tocantins basin and in rio Araguaia; both species do not co-occur. Potamotrygon rex, sp. nov., has a unique blackish to dark brown dorsal color with numerous small, yellow to orange irregular spots usually forming distinct clusters on dorsal disc, with ocelli in center of clusters on posterior and outer disc, dorsal tail also with clusters but lateral tail with ocelli, and a dark brownish to gray color covering most of ventral surface except nasoral region, gill slits and anterior snout in some specimens, with small whitish spots on ventral disc, pelvic fins and tail. Potamotrygon rex, sp. nov., can be further distinguished by its broad pelvic-fin apices, lack of labial grooves, irregular double row of dorsal tail thorns, and in having two angular cartilages associated with each hyomandibula. Potamotrygon rex, sp. nov., P. henlei, P. leopoldi Castex & Castello, and another new Potamotrygon species from the rio Tapajós (in description) form a species-group (the "black stingrays") occurring in rivers draining the central Brazilian shield, characterized by their black to dark brown but highly ornate dorsal color, wide pelvic fins with broadly convex apices, among other features. Potamotrygon rex, sp. nov., is the 25^th species of Potamotrygon, and highlights that very large new species of fishes still await discovery and description in the Neotropical region.

Trends and biases in the scientific literature on Brazilian watersheds

Brazilian watersheds have a high species and natural resources biodiversity. To know the features of scientific production on these regions is important to adjust study focus and to determine publication biases. This study aims at characterizing the scientific literature about Brazilian watersheds on scientometric grounds. For this purpose, we performed a search of articles in the ISI Web of Science database of the Institute for Scientific Information (ISI). The search returned 2,945 articles: 1,613 on the Amazon basin, 584 on the La Plata basin, 262 on the São Francisco basin, 190 on the Tocantins basin, 117 on the Southeast Coastal basin, 70 on the Eastern Northeast Coastal basin, 48 on the Parnaíba basin, 45 on the South Coastal basin, 14 on the North Coastal basin and two on the Western Northeast Coastal basin. The highest number of articles, journal diversity and impact factor was for the Amazon basin. Generally, the increase of the number of articles on the coastal basins over the years is lower. A keyword analysis shows that the study of most basins deals with similar subjects. However, researches on the Amazon and La Plata basins follow lines that are very different both from each other and from the other basins. In view of such results, incentives for new studies must focus on coastal basins. It is also recommended to submit works to good quality journals.

Ecology of Mylesinus paucisquamatus Jégu & Santos, 1988, an endangered fish species from the rio Tocantins basin

ABSTRACT Mylesinus paucisquamatus is a threatened fish endemic to the rio Tocantins basin, with little information about its natural history. Using monitoring data obtained between 1998 and 2009, we investigated the spatial distribution, feeding and reproduction of this species in a long stretch of the middle-upper rio Tocantins. Eighty-one individuals were captured over a decade of intensive sampling. In addition, we recorded the species in only 13 out of 35 sites, particularly in the Tocantins and Paranã rivers. Most individuals were captured alone, while the remaining formed small groups. These results indicate that this fish is rheophilic and rare. We recorded seasonal variation in fish abundance, with higher values during the dry season, indicating seasonal movements. The species is herbivorous and specialized in the consumption of plants attached to substrates, particularly bryophytes. We also observed seasonality in reproduction, since reproductive activity increased during the early dry season. These ecological traits, e.g. , rarity, rheophilic and specialized feeding habits, indicates that M. paucisquamatus is vulnerable to environmental changes, particularly river damming. Considering that three large dams currently regulate and fragment this section of the rio Tocantins, the persistence of this species is jeopardized, demanding effective conservation actions.

Study of the regionalization of characteristic discharges and the water availability in the Upper Tocantins basin

Study of the regionalization of characteristic discharges and the water availability in the Upper Tocantins basin

Feeding and reproductive ecology of Cichla piquiti Kullander & Ferreira, 2006 within its native range, Lajeado reservoir, rio Tocantins basin

Cichla piquiti is endemic to the Tocantins-Araguaia river basin, but information about its biology is restricted to populations introduced in other basins. In order to fill this gap, we investigated the feeding ecology and reproductive dynamics of C. piquiti in Lajeado reservoir, rio Tocantins. A total of 270 fish were collected between November 2010 and October 2011. The diet is rich and composed of at least 23 resources, predominantly fish (at least 19 species). We observed no clear influence of sex, periods and ontogeny on diet, which was basically composed of Characidae and Cichlidae. Considering its reproductive dynamics, immature, reproductive and non-reproductive fish were recorded during the whole study, and reproductive effort did not differ among periods. Cichla piquiti also showed no pattern of energy allocation between reproductive and somatic activities. These results indicate that reproduction is occurring throughout the year and that this activity is not synchronized among individuals. In conclusion, this study presented valuable information on the ecology of C. piquiti within its natural range, which may subsidize management programs to conserve local stocks. This information may also provide theoretical insights to explain why C. piquiti , a voracious predator, is so harmful when introduced in non-Amazonian reservoirs.

Retroculus acherontos, a new species of cichlid fish (Teleostei) from the Rio Tocantins basin.

Retroculus acherontos is described from the Rio Tocantins basin, Brazil. It is distinguished from all congeners by the presence of a nuchal hump in large specimens, an irregular black blotch located on the middle of the anterior soft dorsal-fin rays, fewer pectoral-fin rays (15-16), a deeper body, a convex ventral profile, a more transversely convex ventral surface of the body, and by chest scales similar in size to the scales on the side. An expanded diagnosis for the genus Retroculus is provided.

Rhinolekoscapetinga: a new cascudinho species (Loricariidae, Otothyrinae) from the rio Tocantins basin and comments on its ancestral dispersal route.

The present study deals with the description of a new species of Rhinolekos. It can be distinguished from its congeners by having 31 vertebrae, the anterior portion of the compound supraneural-first dorsal-fin proximal radial contacting the neural spine of the 9th vertebra, the absence of transverse dark bands in the pectoral, pelvic and anal-fin rays, 24–28 plates in the dorsal series, the lack of odontodes on the ventral tip of the snout, the absence of accessory teeth, a greater prenasal length, a smaller head length, and by a greater snout length. Rhinolekos capetinga is restricted to the headwaters of the rio Tocantins and it is the first species of this genus in the Amazon basin. Additionally, we present a brief discussion of a biogeographic scenario that may explain the dispersal of the new species from the rio Paranaíba to the rio Tocantins basin. We suggest that the ancestral lineage of Rhinolekos capetinga reached the rio Tocantins from portions of the rio Paranaíba at the end of the Miocene, about 6.3 Mya (4.1–13.9 Mya 95% HPD), probably as a result of headwater capture processes among adjacent drainages.

Hemigrammus ataktos: a new species from the rio Tocantins basin, central Brazil (Characiformes: Characidae)

A new species of Hemigrammus is described from the middle rio Tocantins basin, central Brazil. The new species can be distinguished from all congeners by having a black midlateral stripe on the body extending from the posterior margin of the eye to the median caudal-fin rays. Mature males possess dorsal-, pelvic-, and anal-fin rays elongate, features that also help to recognize the new species. Although the new species is described in Hemigrammus, some specimens present a complete series of pored scales in the lateral line. A discussion about the generic allocation of the new species is presented.

A new species of Hyphessobrycon Durbin (Characiformes: Characidae) from the middle rio São Francisco and upper and middle rio Tocantins basins, Brazil, with comments on its biogeographic history

A new species of Hyphessobrycon Durbin is described from tributaries of the rio Grande (rio São Francisco basin) draining east to the Serra Geral de Goiás, of the rio São Domingos (upper rio Tocantins basin) and rio do Sono basins (middle rio Tocantins basin). Hyphessobrycondiastatos can be diagnosed from its congeners by the absence of humeral spot, 15-18 branched anal-fin rays, 1-3 maxillary conical to tricuspid teeth, a relatively well-defined dark caudal-peduncle spot, and elongation of dorsal- and anal-fin rays in mature males. The biogeographical significance of the distribution of the new species is evaluated and discussed.

A new species of Microglanis(Siluriformes: Pseudopimelodidae) from the upper rio Tocantins basin, Goiás State, Central Brazil

A new species of Microglanis is described from the upper rio Tocantins basin, Barro Alto, Goiás State, Brazil. This species is distinguished from the others by presenting a unique color pattern, consisting of round spots in the flank between the larger dark brown blotches. Moreover, it can be distinguished by the combination of the following features: caudal fin emarginate, the upper lobe slightly larger than the lower, lateral line relatively long, reaching vertical through posterior margin of the pelvic fin, and light stripe on supra-occipital region absent or very narrow and with irregular shape.

Extreme Rainfall Indices in the Hydrographic Basins of Brazil

The authors analyze climate extremes indices (CEI) of rainfall over the largest basins of the Brazilian territory: Amazon (AMA), S?o Francisco (SF), Tocantins (TO) and Parana (PAR) rivers. The CEI represent the frequency of heavy precipitation events (R30mm and R95p) and short duration extreme rainfall (RX5day and RX1day). Droughts (CDDd) are identified based on two indicators: The longest dry period (CDD) and the annual cycle. The results demonstrate that CDDd, RX1day and RX5day occurred with more frequency and intensity in SF basin during El Ni?o events. CDDd was of greater magnitude in the TO basin during La Ni?a events, while an increase of RX1day occurred in El Ni?o. The strong El Ni?o events (1983 and 1997) caused more intense and frequent RX1day and R30mm over the PAR basin. Amazon droughts occurred in two out of the six El Ni?o events. Moreover, the relationship between the positive (negative) sea superficial temperatures anomalies in North (South) Tropical Atlantic and drought in AMA basin was corroborated. A gradual warming of SST was observed at the start of 2003 until it achieved a maximum in 2005 associated with the southwestern Amazon drought. The second highest anomaly of SST was in 2010 linked with drought that was more spatially extensive than the 2005 drought. The spatial distribution of annual trends showed a significant increase of CDD in south-eastern AMA, Upper SF, northern PAR and throughout the TO basins. R20mm, RX1day and RX5day tend to increase significantly in southwestern (northeast) PAR (AMA) and northwestern TO basins. Comparisons between CEI derived from daily precipitation data from Climate Prediction Center (CPCp) and of the ETA_HadCM3 model showed that the model overestimated RX1day, RX5day and CDD, in the four basins. Future scenarios show that dry periods will occur with greatest magnitude in all the basins until 2071-2099 time slice, while RX1day will be more intense in the TO and SF basins.

The fish fauna of streams from the upper rio Tocantins basin, Goiás State, Brazil

This study aimed to provide a list of fish species from tributaries of rio das Almas and rio Maranhão basins, in the upper rio Tocantins basin, Goiás State, Brazil. For this study 21 stream stretches were sampled during the dry season in July 2010. A total of 2,279 individuals of 67 species, 19 families and five orders were collected. The most representative families in number of species were Characidae, Loricariidae, and Crenuchidae respectively. The genus Knodus, Hypostomus and Characidium showed the greatest abundance and distribution among the samplings. Poecilia reticulata was considered the only non-native species. The presence of a large number of endemic and undescribed species or with undefined taxonomic situation, in addition to the rapid habitat loss in this region, juts the need for the development of further studies in this basin.

A New Genus and Species of a Minute Suckermouth Armored Catfish (Siluriformes: Loricariidae) from the Rio Tocantins Drainage, Central Brazil: The Smallest Known Loricariid Catfish

Nannoplecostomus eleonorae, a new genus and species of a miniature suckermouth armored catfish, is described based on specimens collected from the karst region of Sao Domingos, upper Rio Tocantins basin, Goias State, central Brazil. The new genus and species can be diagnosed among loricariids by presenting a unique reductive pattern of lateral dermal plates, with most of the body covered by only three series of plates (viz., dorsal, mid-ventral, and ventral). Based on the available published phylogenetic studies for the family, we provisionally consider Nannoplecostomus eleonorae as being an incertae sedis taxon within Loricariidae. Achieving a maximum standard length of 22.2 mm SL, Nannoplecostomus eleonorae is the smallest known loricariid catfish, and a list of the remaining smallest loricariids is provided. E descrito um novo genero e especie de cascudo miniaturizado, Nannoplecostomus eleonorae, baseado em especimes coletados na regiao de carste de Sao Domingos, bacia do alto rio Tocantins, estado de ...