Sunday, December 11, 2016

[Ichthyology • 2016] Moenkhausia parecis • A New Species of Moenkhausia Eigenmann (Characiformes: Characidae) from the upper rio Machado at Chapada dos Parecis, rio Madeira Basin, Brazil

Moenkhausia parecis 
Ohara & Marinho, 2016


A new species of Moenkhausia is described from the upper rio Machado at Chapada dos Parecis, rio Madeira basin, Rondônia State, Brazil. Among congeners, the new species is similar to Moenkhausia chlorophthalma, M. cotinho , M. lineomaculata , M. plumbea, and M. petymbuaba by having dark blotches on the anterior portion of the body scales, which are absent in the remaining species of the genus. The new species differs from aforementioned species by possessing blue eyes in life, 15-18 branched anal-fin rays, and a well-defined, round caudal-peduncle spot that does not reach the upper and lower margins of the caudal peduncle and does not extend to the tip of the middle caudal-fin rays.

Key words: Amazon basin; Fish; Moenkhausia cotinho; Ostariophysi; Taxonomy

Diagnosis. Moenkhausia parecis is distinguished from all congeners, except M. clorophthalma Sousa, Netto-Ferreira & Birindelli, 2010, some populations of M. cotinho Eigenmann, 1908(see Discussion), M. lineomaculata [Dagosta, Marinho & Benine, 2015], M. petymbuaba [Lima & Birindelli, 2009], and M. plumbea [Sousa, Netto-Ferreira & Birindelli, 2010] by the presence of a dark blotch on the anterior portion of each scale of the second to seventh longitudinal series (vs. pigmentation absent or, when present, concentrated at the posterior margin of scales, forming a reticulate pattern). Moenkhausia parecis can be readily distinguished from all aforementioned species by having completely blue eyes in life (vs. green in M. clorophthalma, mostly green with some red in M. petymbuaba, lower portion blue and upper portion orange in M. lineomaculata, clear or red in M. cotinho, and clear, with a longitudinal dark stripe in M. plumbea). Additionally, it is distinguished from M. clorophthalma, M. petymbuaba and M. plumbea by having 15-18 (rarely 18) branched anal-fin rays (vs. 18-24), from M. cotinho and M. lineomaculata by having a smaller caudal-peduncle spot, with only the base of the middle caudal-fin rays pigmented (vs. blotch larger, base of all caudal-fin rays pigmented in M. cotinho and M. lineomaculata, except the outermost unbranched rays in some specimens of M. lineomaculata) and by the absence of a light area preceding caudal-peduncle spot (vs . presence of a light area preceding caudal-peduncle spot). It can be further distinguished from M. clorophthalmaM. plumbea and M. plumbea by having a well-defined, round caudal-peduncle spot, that does not extend to the tip of the middle caudal-fin rays (vs . caudal-peduncle spot absent or poorly defined in M. clorophthalma and M. plumbea or caudal-peduncle spot confluent with longitudinal stripe on body, reaching the tip of middle caudal-fin rays in M. plumbea).

Etymology. The specific name parecis refers to the Chapada dos Parecis (plateau including the type locality), an important watershed that separates tributaries of three basins: rio Madeira, rio Tapajós and rio Paraguai. A noun in apposition.

Distribution. Moenkhausia parecis is known only from its type locality, a headwater tributary of igarapé Piracolina, itself a tributary of the upper rio Machado at Chapada dos Parecis, rio Madeira basin, about 9 km south of Vilhena, near the border of Rondônia and Mato Grosso States, Brazil (Fig. 3). Moenkhausia parecis is possibly an additional species endemic to the rivers draining the Chapada dos Parecis(see list in Ohara & Lima, 2015).

Ecological notes. The type locality of Moenkhausia parecis is located at 585 m above sea level on the Chapada dos Parecis. It is a small "terra-firme igarapé" (= highland creek) with little preserved riparian vegetation and surrounded by large plantation fields (mostly soy and corn), near Vilhena, Mato Grosso. It is a clear water stream 1.5-2.5 m wide and 0.3-0.8 m deep, with swift currents, and a bottom composed of sand and dead leaves (Fig. 4). During snorkeling, Moenkhausia parecis was observed in small groups of 10-15 individuals swimming in midwater. Syntopic species included Ancistrus verecundus Fisch-Muller, Cardoso, da Silva & Bertaco, 2005, Bryconops piracolina Wingert & Malabarba, 2011, Cetopsorhamdia sp. 3 (cf. Bockmann & Slobodian, 2013: 25), Corydoras sp., Hyphessobrycon lucenorum Ohara & Lima, 2015, Hyphessobrycon aff. melonostichos Carvalho & Bertaco, 2006 and Pyrrhulina sp. The stomach contents of the four (c&s) paratypes included ants, scales, unidentified insect fragments, seeds, unidentified vegetal fragments and sediments.

Conservation status. Despite intensive and broad collecting efforts in the rio Madeira basin during 2009 to 2013 (Queiroz et al., 2013) and recent surveys conducted in the southeastern portion of Rondônia State and northwest of Mato Grosso State undertaken in 2010-2011 and 2013-2014, Moenkhausia parecis was only collected at its type locality. Additionally, examination of several fish collections failed to reveal additional specimens. Thus, it is possible that the species is restricted to the upper rio Machado, at the Chapada dos Parecis. The type locality of M. parecis is a small forest fragment near Vilhena town that is surrounded by farms. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014), Moenkhausia parecis might be considered as 'Vulnerable (D2)', based on its occupation area (AOO) apparently less than 20 km2 and the plausible future threat (agricultural development and expansion of Vilhena town around its very restricted distribution) that could lead the species to become critically endangered or extinct.

 Willian M. Ohara and Manoela M F Marinho. 2016. A New Species of Moenkhausia Eigenmann (Characiformes: Characidae) from the upper rio Machado at Chapada dos Parecis, rio Madeira Basin, Brazil. Neotropical Ichthyology [Neotrop. ichthyol.]. 14(1); DOI: 10.1590/1982-0224-20150041

RESUMO: Uma espécie nova de Moenkhausia é descrita do alto rio Machado na Chapada dos Parecis, bacia do rio Madeira, Rondônia, Brasil. Entre as congêneres, a espécie nova é semelhante à Moenkhausia chlorophthalma , M. cotinho , M. lineomaculata , M. plumbea e M. petymbuaba por ter manchas escuras na região anterior das escamas, que estão ausentes nas demais espécies do gênero. A espécie nova difere das espécies mencionadas acima por possuir olhos azuis em vida, 15-18 raios ramificados na nadadeira anal e uma mancha arredondada bem definida no pedúnculo caudal, que não alcança o limite superior e inferior do pedúnculo caudal, e não se estende sobre os raios medianos da nadadeira caudal.