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

Sarmento-Soares, Luisa Maria, Cabeceira, Fernando G., Carvalho, Lucélia Nobre, Zuanon, Jansen & Akama, Alberto, 2013, Centromochlus meridionalis, a new catfish species from the southern Amazonian limits, Mato Grosso State, Brazil (Siluriformes: Auchenipteridae), Neotropical Ichthyology 11 (4), pp. 797-808 : 799-804

Centromochlus meridionalis , new species Figs. 1-2

Holotype. INPA 39684 , 40.2 mm SL, Brazil, Mato Grosso, Cláudia, córrego Loanda, a small tributary of rio Roquete , rio Teles Pires basin, 11º25’33.1”S 55º16’39.3”W, 8 May 2011, F. G. Cabeceira & E. Barbosa.

Paratypes. Brazil, Mato Grosso State, rio Teles Pires basin: MNRJ 40699 , 2 , 32.9-40.5 mm SL, MNRJ 40700 , 1 c&s, 38.7 mm SL, INPA 37893 , 10 , 40.4-47.9 mm SL and INPA 37897 , 2 c&s, 29.7-39.2 mm SL, córrego Loanda, a small tributary of rio Roquete, 11º25’ 33.1”S 55º16’39.3”W, 8 May 2011, collected with holotype. INPA 37895 , 1 , 41.7 mm SL, MNRJ 40701 , 1 , 51.8 mm and UNT 12385, 1 , 52.3 mm SL, municipality of Cláudia, córrego Loanda, a small tributary of rio Roquete , 11º25’33.1”S 55º16’39.3”W, 24 Jul 2010, F. G. Cabeceira, W. S. de Moraes & J. Dambroz. INPA 37896 , 1 , 38.6 mm SL and UNT 12386, 2 , 35.8-38.7 mm SL, Municipality of Cláudia , córrego Loanda, a small tributary of rio Roquete , 11º25’42.7”S 55º16’34.6”W, 9 May 2011, F. G. Cabeceira & E. Barbosa. INPA 37895 , 1 , 41.7 mm SL and MNRJ 40701 , 1 , 51.8 mm SL, Municipality of Cláudia , córrego Loanda, a small tributary of rio Roquete , 11º25’33.1”S 55º16’39.3”W, 24 Jul 2010, F. G. Cabeceira, W. S. de Moraes & J. Dambroz. MBML 5616 , 1 c&s, 39.1 mm SL, MBML 5617 , 3 , 32.2-46.2 mm SL, MNRJ 40702 , 3 , 32.6-38.3 mm SL, Municipality of Cláudia , córrego Loanda, a small tributary of rio Roquete , 11º25’33.1”S 55º16’39.3”W, 8 May 2011, F. G. Cabeceira & E. Barbosa. MBML 5615 , 2 , 49.2-49.7 mm SL and UNT 12387, 1 , 39.8 mm SL, Municipality of Cláudia , córrego Loanda, a small tributary of rio Roquete , 11º25’33.1”S 55º16’39.3”W, 8 May 2011, F. G. Cabeceira & E. Barbosa. MBML 5618 , 1 , 61.6 mm SL, and UNT 12388, 1 , 41.8 mm SL, Municipality of Cláudia , affluent of córrego Loanda, tributary of rio Roquete , 11º25’48.7”S 55º20’16.3”W, 6 May 2011, F. G. Cabeceira & E. Barbosa. INPA 37894 , 48.3 mm SL, MBML 5614 , 2 , 43.9-57.2 mm SL and MNRJ 40698 , 1 , 42.5 mm SL, Municipality of Cláudia , rio Renato , 200 meters upstream from confluence with a small tributary, 11º 35’59.1”S 55 o 15’21.0”W, 21 May 2011, F. G. Cabeceira & E. Barbosa. MCP 32975, 6 , 29.3-46.4 mm SL, Municipality of Sinop , Ribeirão Macuco, on road BR- 163, about 74 Km north from Sinop .

Diagnosis. Centromochlus meridionalis is distinguished from all congeners by having eye diameter less than 16% of Head Length (vs. 20-35%). The new species differs from C. heckelii , C. existimatus , C. altae , and C. perugiae by absence of anterior nuchal plate (vs. presence). It is distinguished from C. concolor , C. reticulatus , C. macracanthus , C. punctatus , and C. schultzi , by having smooth anterior margin of dorsal spine (vs. with serrae). From C. romani by a trapezoid quadrate, with metapterygoid in contact with hyomandibula (vs. enlarged quadrate, interposed between metapterygoid and hyomandibula).Further distinguished from C. heckelii and C. existimatus by pectoral-fin spine 20-25% of SL (vs. 29- 42%) and 6 branched anal-fin rays (vs. 4 or 5). The new species is also distinguished from all congeners, except C. perugiae and C. romani , by having male modified anal fin with enlarged third unbranched ray, about twice thicker than first unbranched ray.

Description. Measured adult specimens 32.6-61.6 mm SL; morphometric data inTable 1. Body stout when compared to other centromochlines.Head large, robust, slightly depressed; outline of head in dorsal view elliptic, broader than long. Trunk from dorsalfin base to caudal peduncle gradually compressed. Lateral profile of head from snout tip to opercular margin slightly convex until pectoral-fin insertion.Ventral profile of head and abdomen almost flat.Ventral profile of body gently curved, concave behind anal-fin origin.Head integument thin, cranial roof visible; well-developed adipose eye lid; eye latero-dorsally located in anterior portion of head; mouth terminal, upper lip extended postero-laterally as well-developed fleshy rictal fold; snout margin rounded in dorsal view; anterior nostril tubular, located on anterior border of snout; posterior nostril somewhat larger, rounded, limited by small skin flap; transverse distance between anterior nostrils proportionally shorter than distance between posterior ones. Maxillary barbel short, extending posteriorly close to membranous border of opercle; mental barbel short, tip extending to pectoral-fin base, arranged in arc along ventral surface of jaw; inner mental barbel about two-thirds of length of outer mentals. Posterior process of cleithrum short, almost reaching vertical through insertion of dorsal fin spine.

Rostral border of cranium with mesethmoid longer than broad; premaxilla underneath with synchondral articulation; elliptical cranial fontanel, with irregular narrow opening between mesethmoid and frontals ( Fig. 3 ). Nasal ossified as short tubular bone canal, lying between mesethmoid cornua and lateral ethmoid, not sutured to mesethmoid. Autopalatine as a rod, oriented almost parallel to longitudinal axis of body; maxilla very small, less than half the size of autopalatine; vomer short, with arrow-shaped lateral process. Jaws of equal size; premaxilla and dentary narrow with three or four rows of robust conical teeth. First nuchal plate absent; second nuchal plate slightly concave along lateral margins; third nuchal plate thin, projected laterally, with prominent tip. Epioccipital process very small.

Hyomandibula broad, projected anteriorly, connected to both quadrate and metapterygoid through cartilage and deeply dentate suture. Metapterygoid conical, as a wide lamina, joined to quadrate via dentate suture ( Fig. 4 ). Quadrate trapezoidal, with broad base, connected to preopercle, hyomandibula and metapterygoid; long preopercle ventral margins sutured to both quadrate and hyomandibula; suprapreopercle present as short canal bone; opercle laminate, ornamented and broadly subtriangular.

Hyoid arch with urohyal reduced with a laminate ventral process; short dorsal hypohyal associated with comparatively large ventral hypohyal; anterior ceratohyal well developed, posterior ceratohyal smaller; branchiostegal ray articulated to hyoid arch; branchiostegal rays 6, 3 on anterior ceratohyal, 1 associated with interceratohyal cartilage and 2 posteriormost flattened and associated to posterior ceratohyal.

Branchial (gill) arches with urohyal anterior to basibranchial 2; basibranchial 2 cartilaginous, broadest anteriorly, usually separated by gap from basibranchial 3; basibranchial 3 shorter, forming osseous rod; basibranchial 4 large, flattened and cartilaginous; basibranchial 2 bordered laterally by cartilaginous head of hypobranchial 1; basibranchial 3 between cartilaginous head of hypobranchial 2 and cartilaginous hypobranchial 3; basibranchial 4 bordered laterally by cartilaginous head of ceratobranchial 4 and caudally by cartilaginous head of ceratobranchial 5. Hypobranchials 1 and 2 subtriangular, mostly osseous, elongate and expanded laterally, with cartilaginous tips; hypobranchial 3 completely cartilaginous, trapezoidal; hypobranchial 4 absent. Five ceratobranchials, mostly ossified, with cartilage on both ends. First and second ceratobranchials supporting single row of rakers; third and fourth ceratobranchials with two rows of rakers; fifth ceratobranchial supporting single row of rakers, expanded postero-medially to support lower pharyngeal toothplate with short conical teeth. Four epibranchials, all largely ossified except for cartilaginous ends, supporting one or two rakers each, close to articulation with ceratobranchials. Epibranchials 1 and 2 rod-like; epibranchial 3 with posterior uncinate process in articulation to epibranchial 4; epibranchial 4 with laminar extension; reduced accessory cartilage, located on angle between cartilaginous ends of epibranchial 4 and ceratobranchial 4. Pharyngobranchial 1 absent; pharyngobranchial 2 short, cartilaginous, somewhat ellipsoid, placed between anteromedial cartilaginous tips of epibranchials 1 and 2; pharyngobranchial 3 elongate, ossified, with expanded posterior border; pharyngobranchial 4 ossified. Upper pharyngeal tooth plate with conical teeth, supported by pharyngobranchial 3 and 4, and also epibranchials 3 and 4.

Infraorbital 1 with ventro-lateral process restricted to anterior border of eye. Subsequent three infraorbitals thin and canal-like, in complete infraorbital series. Lateral line on body straight, inconspicuous, with ossified canal bones only anteriorly, unbranched at caudal fin.

Dorsal fin I,5, dorsal spine smooth anteriorly, posterior margin with minute serrations becoming progressively small towards fin base. Pectoral fin I,5, pectoral spine with 10-16 serrations along entire anterior margin, proximal ones retrorse, distal ones antrorse; 9-10 retrorse serrations along posterior margin; serrations on anterior margin smaller than posterior. Pelvic-fin i,5, margin rounded. Adipose fin small, origin at vertical through anal-fin base. Anal fin iii,6-7; analfin pterygiophores in eight rod-like proximal radials and seven cartilaginous distal radials. Caudal fin deeply forked, lobes with rounded tips, 8+9 principal rays, 17 upper and 17 lower procurrent rays.

Ribs 7, becoming progressively smaller posteriorly. Total vertebrae 29 (N = 2).

Sexual dimorphism. Based on examination of gonads, C. meridionalis attains sexual maturity around 30-35 mm SL. In females a genital papilla is prominent, with a small fleshy tissue around opening. The genital papilla of mature males is visible as an emergent deferent duct ( Fig. 5 , dd). The anal fin of mature males is strongly modified with all proximal radials basally fused to each other, forming a single ossification.Third unbranched ray elongated and thickened,ending in a rounded tip, together with the slim first branched ray ( Fig. 5 , uiii, b1). First unbranched anal-fin ray thickened and short. Second unbranched ray elongated, with an intermediate size between the neighboring first and third rays. Third unbranched ray longest, twice the width of first branched ray, bearing 13-15 segments ( Fig. 5 , uiii, b1). Posterior branched rays progressively shorter; last ray the smallest ( Fig. 5 , b 6 ). No tegumentary keel preceding the first unbranched anal-fin ray. No modifications observed in the maxillary barbel and in the dorsal spine of males, as is usual in someAuchenipteridae, where transformed males have stiff, ossified maxillary barbels, and an elongated dorsal-fin spine (recent reports in Ferraris & Vari, 1999; Reis & Borges, 2006; Ribeiro & Py-Daniel, 2010).

Color in alcohol. Color dark brown with wavy longitudinal pale bands on dorsal shield and mid-dorsal portions of body; dorsal surface of head and dorsal fin largely dark brown; sides of body with dark brown dots, becoming sparse towards belly. Paired and anal fins pale brown with hyaline tips. Caudal fin hyaline with irregular blackish brown spots.

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 1 st and 2 nd 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.

Figures

Fig. 1. Centromochlus meridionalis, new species, holotype, INPA 39684, male, 40.2 mm SL, córrego Loanda, a small tributary of rio Roquete, rio Teles Pires basin, Municipality of Cláudia, Mato Grosso State, Brazil. Lateral, dorsal and ventral views.

Fig. 2. Centromochlus meridionalis, new species, paratype, INPA 37894, female, 57.2 mm SL, rio Renato, rio Teles Pires basin, Municipality of Cláudia, Mato Grosso State, Brazil, in lateral, dorsal and ventral views.

Fig. 3. Neurocranium ofCentromochlus meridionalis, MBML 5616, paratype, 39.1 mm SL. Dorsal view. Abbreviations: ep, epioccipital; fo, cranial fontanel, fr, frontal; le, lateral ethmoid; me, mesethmoid;na, nasal;n2, second nuchal plate; n3, third nuchal plate; pe, posterior epioccipital process; ps, posttemporal-supracleitrum; pt, pterotic; so, supraoccipital; sp, sphenotic. Scale bar = 1 mm.

Fig. 4. Right suspensorium of Centromochlus meridionalis, MBML 5616, paratype, 39.1 mm SL. Lateral view. Abbreviations: aa, angulo-articular; dn, dentary; hy, hyomandibula; io, interopercle; mt, metapterygoid; op, opercle; po, preopercle; qu, quadrate; sb, subpreopercle; sp, suprapreopercle. Scale bar = 1 mm.

Fig. 5. Male modified anal fin of Centromochlus meridionalis, MBML 5616, paratype, 39.1 mm SL. Left side lateral view. Abbreviations:b1, branched first ray; b6, branched sixth ray; dd, deferent duct; Dr, distal radials; Pr, proximal radials; ui, unbranched first ray; uii, unbranched second ray; uiii, unbranched third ray. Scale bar = 1 mm.

Fig. 6. Centromochlus meridionalis, living specimen photographed in a field aquarium just after collection.

Fig. 7. Map of rio Teles Pires drainage and rio Tapajós headwaters illustrating collecting sites of Centromochlus meridionalis. Red lozenge in square indicates type locality. Yellow circles refer to paratypes localities. Some symbols may represent more than one collecting locality.

Fig.8. Detail ofcórregoLoanda,typelocality ofCentromochlus meridionalis, rio Teles Pires Basin, municipality of Cláudia, Mato Grosso State, Brazil.