Tuesday, December 1, 2015

[Ichthyology • 2013] Centromochlus meridionalis • A New Catfish Species (Siluriformes: Auchenipteridae) from the Southern Amazonian Limits, Mato Grosso State, Brazil

Centromochlus meridionalis
Sarmento-Soares, Cabeceira, L. N. Carvalho, Zuanon & Akama, 2013

Centromochlus actually comprises eleven species, being the most problematic genus among the Centromochlinae, including morphologically heterogeneous taxa. The Centromochlus species have a wide distributional area on northern South America. Centromochlus meridionalis, new species, is described from headwaters of rio Teles Pires, contributor of rio Tapajós, Mato Grosso State, Brazil, and represents one of the southernmost records of a centromochlin catfish for Meridional Amazon rivers. Centromochlus meridionalis is promptly distinguished from its congeners by the small orbital diameter (relative to head length), and also by the combination of absence of first nuchal plate, anterior margin of dorsal-fin spine smooth, six branched rays in anal fin, seven pairs of ribs and 34 vertebrae. They are small sized catfishes with adults between 33 to 61 mm in standard length. The modified male anal fin is conspicuous, with the third unbranched ray enlarged, about twice the width of first unbranched ray. The new species inhabits a region strongly endangered by environmental changes due to expansion of agropecuary activities on Brazilian Amazon, which include this species in an uncertain situation regarding the conservation status of its natural population.

Key words: Amazon; Centromochlinae; Forest streams; Taxonomy; Teles Pires

Live coloration. Body color dark brown mottled in black, in a reticulated pattern, on dorsal shield and mid-dorsal portions of body. Mid-ventral portions of body with scattered brown chromatophores. Fins almost hyaline, where principally the rays are mottled with pale brown spots towards base. Ventral surfaces white somewhat translucent with little scattered brown chromatophores (Fig. 6). Overall body color strongly reminiscent of that of species of Trachelyopterus, possibly due to life style associated to submersed litter banks.

Distribution. Centromochlus meridionalis was recorded so far only from headwater streams of the upper reaches of rio Tapajós, at the rio Teles Pires, Mato Grosso State (Fig. 7). Regarding global biogeographic regionalization of freshwater systems, the new species occurs in the Tapajós-Juruena ecoregion (sensu Abell et al., 2008).

Ecological notes. Centromochlus meridionalis was captured in 1st and 2nd order streams, with 1.22 to 3.16 m in width and 0.17 to 0.72 m in depth, characterized by clear water and slow current that varies from 0.15 to 0.36 cm/s, over sand bottom with litter, and riparian surrounding vegetation (Fig. 8). The fishes were captured under trunks and principally inset somewhat compressed submerged litter banks. It is a micro generalist carnivore that eat small fish (Moenkhausia phaeonota, Characidae), shrimps, aquatic insect larvae and nymphs, fragments of terrestrial arthropods (ants, spiders), seeds and particulate organic matter (Cabeceira et al., in prep.). Specimens of Centromochlus meridionalis have nocturnal habits and in aquarium conditions sowed a peak of activity in the evening instead of dusk like other Centromochlinae, and it finds shelter under amidst submerged leaf litter banks before daylight (Cabeceira et al., in prep.). The new species was collected syntopically with Astyanax sp., Bryconops spp., Knodus heteresthes, Moenkhausia spp., Erythrinus erythrinus, Hoplerythrinus unitaeniatus, Rivulus kayabi, Gymnotus aff. carapo, Gymnorhamphichthys petiti, Eigenmannia aff. trilineata, Aequidens sp., Crenicichla inpa, Tatia strigata, Tatia neivai, Helogenes marmoratus, Cetopsis sandrae, small unidentified cetopsid, Hisonotus spp., Cetopsorhamdia sp., Imparfinis aff. stictonotus, Phenacorhamdia somnians, Rhamdia quellen, Ituglanis aff. amazonicus, and Synbranchus sp. (F.G. Cabeceira, unpublished data).

Etymology. The specific name makes reference to the record of a Centromochlus species in southern Brazilian Amazon, a region referred to as "Meridional Amazon". Other Centromochlus species were recorded for southern Amazon, such as C. schultzi from upper Xingu and C. perugiae, from Rondônia and herein registered for southwestern Mato Grosso State.These two species, however, have a wide distributional range, respectively along central brazilian plateau and also western Amazon and upper Paraguay. On the other hand, Centromochlus meridionalis is the single species in the genus originally described from Meridional Amazon, and with distribution apparently restricted to this region.

Sarmento-Soares, L.M., Cabeceira, F.G., Carvalho, L.N., Zuanon, J. & Akama, A. 2013. Centromochlus meridionalis, A New Catfish Species from the Southern Amazonian Limits, Mato Grosso State, Brazil (Siluriformes: Auchenipteridae). Neotropical Ichthyology. 11 (4): 797-808. DOI:   10.1590/S1679-62252013000400007

Centromochlus abriga atualmente onze espécies, sendo o gênero mais problemático dentre os Centromochlinae, incluindo táxons morfologicamente heterogêneos. As espécies de Centromochlus apresentam uma ampla área de distribuição no norte da América do Sul. Centromochlus meridionalis, espécie nova, é descrita para as cabeceiras do rio Teles Pires, formador do rio Tapajós, Mato Grosso, Brasil, e representa um dos registros mais ao sul de um bagre centromoclíneo para os riachos da Amazônia meridional. Centromochlus meridionalis é prontamente distinguido de todos os seus congêneres, pelo diâmetro orbital pequeno (em relação ao comprimento da cabeça), e ainda pela combinação da ausência de primeira placa nucal, margem anterior do espinho da nadadeira dorsal lisa, seis raios ramificados na nadadeira anal, sete pares de costelas e 34 vértebras. São bagres de pequeno porte com adultos entre 33 e 61 mm de comprimento padrão. A nadadeira anal de machos sexualmente maduros é conspicuamente modificada, na qual o terceiro raio indiviso é muito largo, cerca do dobro da espessura do primeiro raio ramificado. O registro desta espécie nova ocorre em uma região fortemente ameaçada por alterações ambientais decorrentes da expansão de atividades agropecuárias na Amazônia Brasileira, a qual coloca esta espécie em uma situação incerta quanto ao estado de conservação da sua população natural.