Centromochlus britskii, Sarmento-Soares & Birindelli, 2015

Sarmento-Soares, Luisa Maria & Birindelli, José Luís Olivan, 2015, A new species of the catfish genus Centromochlus (Siluriformes: Auchenipteridae: Centromochlinae) from the upper rio Paraná basin, Brazil, Neotropical Ichthyology (Neotrop. Ichthyol.) 13 (1), pp. 77-86 : 79-83

Centromochlus britskii , new species

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Fig. 1

Glanidium cesarpintoi (non Ihering, 1928). -Sarmento-Soares & Buckup, 2005: 846 (comparative material).

Holotype. MZUSP 115271 , 39.2 mm SL, male, Brazil, São Paulo, rio Paraná where is now the UHE Ilha Solteira upper rio Paraná basin, approximately 20°18’S 51°10’W, Sep 1965, Excursion of Departamento de Zoologia da Secretaria de Agricultura do Estado de São Paulo, Heraldo A. Britski, Izáurio A. Dias & Gustavo A. S. de Melo.

Paratypes. MZUSP 43251 , 2 R + 1 CS, 33.5-36.3 mm SL, MNRJ 41787 , 2 R, 36.0- 38.6 mm SL, collected with holotype, prior to the river dam .

Diagnosis. Centromochlus britskii is distinguished from all Centromochlinae , except Gelanoglanis nanonocticolus Soares-Porto, Walsh, Nico & Netto, 1999 , by absence (vs. presence) of adipose fin. The new species differs from G. nanonocticolus by having two pairs (vs. one pair) of mental barbels, premaxillary tooth patches anteriorly united (vs. separated) and mouth gape straight and short (vs. large and sinuous).

The new species differs from congeners Centromochlus altae , C. existimatus , C. heckelii , C. perugiae , C.reticulatus , C. romani and C. meridionalis by having seven branched rays in the anal fin (vs. 5 or 6). Further distinguished from C. altae , C. existimatus , C. heckelii and C. perugiae by lacking anterior nuchal plate (vs. anterior nuchal plate present); from C. meridionalis and C. romani by having anterior margin of dorsal-fin spine with serrae (vs. dorsal-fin spine smooth); from C. existimatus and C. heckelii by having shorter pectoral-fin spine 20.7-22.7% of SL (vs. 29.3-41.6% of SL).

Among species group that share the absence of anterior nuchal plate and seven branched anal-fin rays (i.e, C. punctatus , C. schultzi , C. macracanthus , C. bockmanni , C. simplex ), the new species differs from both C. schultzi and C. macracanthus by having posterior border of dorsalfin spine smooth (vs. with denticules); from C. punctatus by the morphology of male modified anal fin, specifically, the last branched anal-fin ray progressively shorter than anterior most (vs. last ray abruptly reduced, size half that of preceding one and visible only through dissection).

Description. Morphometric data in Table 1 . Small size, examined adult specimens 33.6-39.2 mm SL. Body short, head slightly depressed. In dorsal view, profile of head longer than broad, slightly convex from snout tip to pectoral-fin insertion. In lateral view, dorsal profile of body from dorsalfin base to caudal fin slightly to distinctly convex. Ventral profile of head and abdomen almost straight. Ventral profile of body gently concave between anal-fin base and caudalfin origin. Trunk from dorsal-fin base to caudal peduncle gradually compressed. Head integument thick, bones of cranialroofnotdiscernible; adiposeeyelidweaklydeveloped; eye dorsolateral on anterior portion of head; mouth terminal, upper lip extended posterolaterally, fleshy rictal fold well developed; snout margin rounded in dorsal view; anterior nostril tubular, located on anterior border of snout; posterior nostril somewhat larger, rounded, limited anteriorly by small skin flap; transverse distance between anterior nostrils almost equal to distance between posterior ones. Maxillary barbel elongate, extending well beyond membranous border of opercle, reaching approximately vertical through dorsalfin origin; adpressed maxillary barbel fits in groove on the lateral portion of head, immediately above rictal fold and below eye; mental barbels short, tips not reaching pectoralfin base; bases of barbels arranged in arc along ventral surface of jaw; inner mental barbel about two-thirds outer mental. Posterior process of cleithrum moderately large, almost reaching vertical through base of dorsal-fin spine.

Osteological description. Rostral border of cranium with mesethmoid longer than broad; premaxilla with synchondral articulation; cranial fontanel narrowly elliptical, enclosed by mesethmoid and frontals ( Fig. 2 ). Nasal ossified as short tubular bone situated between mesethmoid cornua and lateral ethmoid, not sutured to mesethmoid. Autopalatine rod-like, oriented almost parallel to longitudinal axis of body; maxilla very small, less than half the size of autopalatine; vomer short, arrow-shaped with lateral processes. Jaws of equal size; premaxilla and dentary slender with three or four rows of robust conical teeth. Anterior nuchal plate absent; middle nuchal plate slightly concave along lateral margins; posterior 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 as a wide lamina, joined to quadrate via suture ( Fig. 3 ). Quadrate trapezoidal, with broad base, sutured 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 parurohyal well developed with a robust ventral process; short dorsal hypohyal associated with comparatively large ventral hypohyal; anterior ceratohyal well developed, posterior ceratohyal smaller than others one; branchiostegal ray articulated to hyoid arch; six branchiostegal rays, four slender rays associated with anterior ceratohyal, two flattened rays with posterior ceratohyal ( Fig. 4 ).

Branchial (gill) arches with urohyal close 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. Ceratobranchials supporting single row of rakers; fifth ceratobranchial expanded postero-medially to support lower pharyngeal toothplate with short conical teeth. Four epibranchials, all largely ossified except for cartilaginous ends, supporting few 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 ( Fig. 5 ).

Infraorbital 1 with ventro-lateral process restricted to anterior border of eye. Infraorbital series completed by four thin and canal-like bones. Lateral line on body straight, inconspicuous, with ossified canal bones only anteriorly, unbranched at caudal fin.

Dorsal fin I,5, dorsal-fin spine with 9 minute serrations becoming progressively smaller towards fin base; spine smooth anteriorly and posteriorly. Pectoral fin I,5, pectoral-fin spine with 16-17 retrorse serrations along entire anterior margin; 13 retrorse serrations along posterior margin; anterior serrations smaller than posterior ones. Pelvic-fin i,5, lateral margin rounded. Adipose fin absent in all specimens. Anal fin iii,7; anal-fin pterygiophores with eight rod-like proximal radials and six cartilaginous distal radials. Caudal fin deeply forked, lobes with rounded tips, 8+9 principal rays, all branched plus first branched in each lobe; 10-14 upper and 8-13 lower procurrent rays.

Ribs 9 (one specimen with 10) attached to consecutive vertebrae 6-14, becoming progressively smaller posteriorly. Total vertebrae 32 (N= 2) or 33 (3), observed in cleared and stained (CS) and radiographed specimens (R).

Color in alcohol. Color dark brown with chromatophores scattered on the head and mid-dorsal portions of body; dorsal surface of head and mid-dorsal line darker, with more concentrated chromatophores. Sides of body with light brown chromatophores, becoming sparse towards belly. Fins almost hyaline; rays mottled with pale brown spots along base. Caudal-fin base with irregular black to brown spots; fin becoming hyaline towards distal margin.

Sexual dimorphism. Based on examination of gonads, Centromochlus britskii attains sexual maturity at about 33.0 mm SL. Abdominal cavity previously opened in all specimens, revealing most to be adults, the smallest one a maturing female. Genital papilla prominent with a small fleshy tissue around opening in females. The genital papilla of mature males is visible as an emergent deferent duct ( Fig. 6 , dd). The anal fin of mature males is strongly modified with all proximal radials basally fused to each other, forming a singular structure. Third unbranched ray elongated and thickened, ending in a rounded tip, together with the slim first branched ray ( Fig. 6 , 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. 6 , uiii, b1). Posterior branched rays progressively shorter; last ray the smallest one ( Fig. 6 , b 7 ). No tegumentary keel preceding the first unbranched anal-fin ray; denticulations absent from anterior rays. No modifications observed in the maxillary barbel and in the dorsal-fin spine of males, unlike some species of Auchenipteridae (e.g., Auchenipterus ), wherein modified males have stiff and/or spiny ossified maxillary barbels, and an elongated dorsal-fin spine (Ferraris & Vari, 1999; Reis & Borges, 2006; Ribeiro & Rapp Py-Daniel, 2010).

Distribution. Centromochlus britskii is known from its type locality in the rio Paraná basin near Ilha Solteira, where now is the reservoir of the UHE Ilha Solteira ( Fig. 7 ), in the upper rio Paraná basin, São Paulo, Brazil.

Ecological notes. The species is known only from a single sample in 1965, prior to the completion of UHE Ilha Solteira; specimens were collected in places with rocks and rapids near cofferdams in the main channel of the upper rio Paraná. The rio Paraná in that area is now modified as a large reservoir. Analysis of the stomach contents revealed the presence of insect larvae, including Chironomidae , and other invertebrate fragments.

Etymology. The specific name honors Dr. Heraldo Antonio Britski, who collected the type material, for his significant contributions and pioneer studies on the systematics of the catfish family Auchenipteridae (i.e, Britski, 1972).

Figures

Fig. 1. Centromochlus britskii, new species, holotype, MZUSP 115271, male, 39.2 mm SL, UHE Ilha Solteira, upper rio Paraná basin, Ilha Solteira, São Paulo State, Brazil. Lateral (a), dorsal (b) and ventral (c) views.

Fig. 2. Neurocranium of Centromochlus britskii, MZUSP 43251, paratype, 35.9 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. 3. Right suspensorium of Centromochlus britskii, MZUSP 43251, paratype, 35.9 mm SL. Lateral view. Abbreviations: aa, angulo-articular; dn, dentary; hy, hyomandibula; io, interopercle; mt, metapterygoid; ms, mesopterygoid; op, opercle; po, preopercle; qu, quadrate; sb, subpreopercle; sp, suprapreopercle. Scale bar = 1 mm.

Fig. 4. Right hyoid arch of Centromochlus britskii, MZUSP 43251, paratype, 35.9 mm SL. Ventral view. Abbreviations: ac, anterior ceratohyal; br, branchiostegal rays; dh, dorsal hypohyal; ic, interceratohyal cartilage; ih, interhyal; pc, posterior ceratohyal; vh, ventral hypohyal; uh, urohyal; up, urohyal ventral process. Scale bar = 1 mm.

Fig. 5. Pharyngeal arches of Centromochlus britskii, MZUSP 43251, paratype, 35.9 mm SL. Dorsal view. Abbreviations: bb2, basibranchial 2; bb3, basibranchial 3; bb4, basibranchial 4; cb1-5, ceratobranchials 1 to 5 (anterior to posterior); eb1-4, epibranchials 1 to 4 (anterior to posterior); hb1-3, hypobranchials 1 to 3; pb3, pharingobranchial 3; pb4, pharingobranchial 4. Scale bar = 1 mm.

Fig. 6. Male modified anal fin of Centromochlus britskii, MZUSP 43251, paratype, 38.6 mm SL. Left side in lateral view. Abbreviations: b1, first branched ray; b7, seventh branched ray; dd, deferent duct; pr, unsegmented procurrent anal fin rays (not counted); ui, unbranched first ray; uii, second unbranched ray; uiii, third unbranched ray. Scale bar =1 mm.

Fig. 7. Map of southeast South America indicating the rio Paraná in UHE Ilha Solteira, type-locality of Centromochlus britskii.