Scobinancistrus raonii, Chaves & Oliveira & Gonçalves & Sousa & Py-Daniel, 2023

Chaves, Mateus S., Oliveira, Renildo R., Gonçalves, Alany P., Sousa, Leandro M. & Py-Daniel, Lúcia H. Rapp, 2023, A new species of armored catfish of the genus Scobinancistrus (Loricariidae: Hypostominae) from the Xingu River basin, Brazil, Neotropical Ichthyology (e 230038) 21 (3), pp. 1-19 : 4-11

Scobinancistrus raonii , new species urn:lsid:zoobank.org:act:A7052468-F11E-4AE8-BFFD-C2658EA8F86A

( Figs. 1–3 ; Tab. 1)

L082 Ancistrinae gen. sp. —Schraml, Schäfer, 2004:79–80 (Aquarium fish atlas; citation and brief description).

Ancistrini sp. (L 82). —Seidel, Evers, 2005:936–38 (Wels atlas; citation and brief description).

L082. —Seidel, 2008:198 (citation and brief description; figs. 1–3). —Camargo et al., 2012:113–18 (Book).

Scobinancistrus sp. 2 “Arábia ou Tubarão”. —Gonçalves et al., 2009:239 (Book chapter). —Camargo et al., 2012:183 (Book chapter).

Gênero novo, “Arábia”, L082. —Camargo et al., 2012:167–68 (Book, ornamental fish).

Scobinancistrus sp. L82. —Ramos et al., 2015:96 (Article).

Scobinancistrus n. sp. Xingu L082. —Lujan et al., 2015:282 (Article). —Lujan et al., 2017:330 (Article).

Holotype. INPA 59493, 99.6 mm SL, Brazil , Pará , Senador José Porfírio, Xingu River, about 3.5 km downstream from BR-230, 03°06’18.90”S 51°43’28.30”W, 19 Nov 2014, M. H. Sabaj, L. M. Sousa & A. P. Gonçalves .

Paratypes. All from Brazil , Pará , Xingu River . ANSP 193045, 1, 75.3 mm SL, 50 km southeast from Altamira , 03°39’19.4”S 52°23’30.1”W, 11 Oct 2012, M. H. Sabaj, M. Arce & L. M. Sousa. ANSP 194819, 1, 109.3 mm SL, low portion of the main channel going from northwest to southwest, 43 km from Altamira, 03°34’05.0”S 52°20’46.1”W, 11 Sep 2013, M. H. Sabaj, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito, A. Oliveira & R. Robles. ANSP 194989, 1, 121.5 mm SL, middle of Volta Grande, area of rocks in the main channel of the largest branch of the river between the mouths of the rio Bacajaí and the rio Bacajá , 03°31’55.5”S 51°45’41.3”W, 17 Sep 2013, M. H. Sabaj, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito, A. Oliveira & R. Robles. ANSP 200828, 1, 69.7 mm SL, Gorgulho da Rita , conglomerate rocks exposed on the main channel arm, 15 km south of Altamira , 03°20’32.1”S 52°11’09.8”W, 25 Sep 2015, M. H. Sabaj, M. Arce, L. M. Sousa, M. Kalacska, J. P. Arroyo & O. Lucanus. INPA 31426, 1, 75.2 mm SL, Landi waterfall, 03°35’01”S 51°49’21”W, 8 Nov 2008, L. Rapp Py-Daniel, R. R. de Oliveira, J. Bessa & H. Anatole. INPA 31459, 1, 55.1 mm SL, Itaobinha, Pedral, 02°53’22”S 51°56’26”W, 4 Nov 2008, L. Rapp Py-Daniel, R. R. de Oliveira, J. Bessa & H. Anatole. INPA 31787, 1, 91.6 mm SL, Merence Island (Pontão), 03°06’18.0”S 51°43’33.6”W, 5 Nov 2008, L. Rapp Py-Daniel, R. R. de Oliveira, J. Bessa & H. Anatole. INPA 31789, 3 (1 skel., 78.4 mm SL, 2 alc.), 74.0– 120.2 mm SL, Babaquara, Gorgulho da Rita , 03°22’22.3”S 52°11’51.0”W, 7 Nov 2008, L. Rapp Py-Daniel, R. R. de Oliveira, J. Bessa & H. Anatole. INPA 40117, 2, 60.2–67.8 mm SL, low portion of the main channel, 43 km southwest of Altamira , 03°34’04”S 52°20’45”W, 11 Sep 2013, M. H. Sabaj, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito, A. Oliveira, R. Robles & fishermen. INPA 40383, 1, 125.1 mm SL, a central area of the Volta Grande, on the right margin of the main arm of the Xingu, above of mouth of the Bacajá River , 03°31’55”S 51°45’41”W, 17 Sep 2013, M. H. Sabaj, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito, A. Oliveira, R. Robles & fishermen. INPA 40512, 1, 80.9 mm SL, deep channel, 38 km southeast of Vitória do Xingu , 03°05’32”S 51°44’14”W, 21 Sep 2013, M. H. Sabaj, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito, A. Oliveira & R. Robles. INPA 40766, 1, 102.3 mm SL, downstream Volta Grande, narrow region of the main channel, 03°11’03”S 51°37’02”W, 28 Sep 2013, M. H. Sabaj, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito, A. Oliveira & R. Robles. INPA 47255, 1, 72.0 mm SL, channel Gorgulho da Rita , ca. 15 km from Altamira, 03°20’32”S 52°11’10”W, 5 Nov 2014, M. H. Sabaj, L. M. Sousa, R. R. de Oliveira, A. Gonçalves, D. Fitzgerald, V. Machado & P. Madoka Ito. INPA 52347, 1, 120.9 mm SL, Santo Antônio, 03°06’0.7”S 51°46’25.3”W, 5 Sep 2012, E. D. Ribeiro & L. Sousa. INPA 58778, 1, 120.4 mm SL, near Paquiçamba Indigenous Land, at the island, 03°23’42.4”S 51°43’35.6”W, 20 Oct 2013, A. Gonçalves & P. Trindade. INPA 58779, 2, 92.9–129.7 mm SL, Pimental cofferdam, 03°26’22.4”S 51°57’27.9”W, Oct 2010, A. Gonçalves & P. Trindade. LIA 5054, 1, 94.4 mm SL, rio Xingu , right area Gorgulho da Rita, ca. 15 km south-southeast of Altamira, 03°20’51.4”S 52°10’56.1”W, 5 Nov 2014, M. H. Sabaj, L. M. Sousa & A. P. Gonçalves. LIA 6912, 1, 88.4 mm SL, Espelho Waterfall, 03°39’05.2”S 52°22’42.6”W, 30 Sep 2017, L. Sousa. MZUSP 107209, 5, 100.9– 124.9 mm SL, below Volta Grande do Xingu, Pontão, Belo Monte, 03°06’49.0”S 51°43’23.0”W, 12 Jul 2010, Equipe ECIX .

Non-types. Brazil, Pará, Xingu River. INPA 54819, 11, 71.7–166.2 mm SL, Altamira, uncertain location.

Diagnosis. Scobinancistrus raonii differs from its congeners by presenting a deeper caudal peduncle, 11.7–13.5% in SL (vs. 9.8–11.7% in S. aureatus and 9.9–11.4% in S. pariolispos ); by having large yellow irregularly shaped and widely spaced spots over entire body, spots larger than pupil diameter (vs. spots smaller than pupil diameter and densely packed); by presenting last dorsal-fin ray not reaching adipose-fin plate when adpressed in specimens larger than 80 mm SL (vs. last dorsal-fin ray reaching adipose-fin plate when adpressed in young and adults); by lacking contact between hyomandibular and quadrate posteroventrally (vs. contact present). Additionally, S. raonii differs from S. aureatus by lacking a yellow large distal band on the dorsal and caudal fins (vs. present).

Description. Morphometric and meristic data in Tab. 1. Thirty-eight specimens examined and measured. Small to medium-sized Scobinancistrus , largest specimen measured reached 166.2 mm SL (INPA 54819). Body bulky, ellipsoid and rounded in cross section; evenly deep post-cranially. Snout triangular to hexagonal in dorsal view; head and snout elongate, slightly depressed. Lateral view with subtle elevation from snout tip to orbit; slight elevation from this point to dorsal-fin origin, declining from this point to dorsal procurrent caudal-fin ray; complete dorsal profile almost straight or slightly convex. Body wider in cleithrum, deeper at dorsal-fin origin. Ventral surface flat, straight from snout to caudal fin.

Orbit not elevated, eye dorsolaterally positioned. In lateral view, eye inserted on vertical through branchial opening. Interorbital area flattened. Inconspicuous odontodes on cheek plates on young individuals; in larger specimens, cheek odontodes weakly developed, not surpassing branchial opening. Opercle eversible, not exposed; supraopercle area covered by several small plates, some fused. Parieto-supraoccipital almost flat, indistinct from rest of skull bones. Parieto-supraoccipital process small but conspicuous, pointed posteriorly, not elevated, located between first pair of predorsal plates.

Predorsal area short with subtle elevation, with three pairs of plates: first pair of moderately-sized plates divided by parieto-supraoccipital process; second pair almost indistinct; third pair with large, rectangular spaced plates immediately anterior to nuchal plate. Nuchal plate small, anterior to dorsal spinelet.

Mouth and lips moderate in size; oral disc almost round, slightly rectangular. Lips densely covered by small round papilla (papilla larger medially); small papilla surrounding mandibles. Lower lip short, not reaching scapular girdle. Maxillary barbel short, thick at insertion, thin distally, not reaching beyond lower lip border.

Buccal teeth long, strong, and bicuspid. Teeth spatulate with asymmetric dental cusp, with vertical divide between cups ( Fig. 3 ). Mesial cusp much larger than lateral cusp, in young and adults. Dentary cups set apart, almost parallel to each other; premaxillary cups small, closely attached; up to 4 teeth in premaxilla and dentary. Several oral papillae set immediately posterior to premaxilla and dentary organized as a block.

Body smooth, almost without keels; light carena along dorsal-fin base until adipose fin. First mid-lateral plates swiftly bent, forming delicate keel. Ventral surface of caudal peduncle flattened, slightly round. Rest of body without keels or carena. Dorsally, head and trunk completely covered by large plates, except by naked area surrounding dorsal-fin base. Ventral surface utterly devoid of plates in juveniles (up to 70 mm SL) until urogenital opening. Larger specimens (70 to 110 mm SL) with small plates only on lateral border of abdomen, also dispersed on scapular girdle area. Specimens larger than 110 mm SL with small plates covering scapular girdle completely, between pelvics towards urogenital papilla, forming elongate and narrow abdominal plated area; remaining abdomen naked, unplated. Caudal peduncle deep, short, compressed, bulky and wholly plated. Twenty-seven median plates. Posterior plates strongly marked with lines of more developed odontodes on males. Five rows of plates on caudal peduncle. Odontodes short, poorly developed.

Dorsal-fin origin slightly anterior to vertical through pelvic-fin origin. Dorsal fin II,7; locking mechanism present, not functional. Dorsal-fin height moderate; last dorsal-fin ray not reaching adipose-fin supporting plate when adpressed. Dorsal fin without posterior hypertrophied membrane; five to eight plates between last dorsal-fin ray and adipose fin; inter-dorsal area flattened. Adipose fin small with posterior membrane weakly developed. Two pairs of dorsal plates between adipose fin and first dorsal procurrent caudal-fin ray. Caudal fin i,14,i, bilobed, slightly emarginate, with unbranched dorsal caudal-fin ray shorter than unbranched ventral caudal-fin ray. Pectoral fin I,6; pectoral spine short to moderate in size, reaching but not surpassing pelvic-fin base when adpressed. Pectoral spine robust, strong, covered by odontodes; odontodes larger and flexible distally. Pelvic fin i,5, reaching posteriorly vertical through adipose-fin base, not beyond. Anal fin short, i,4. All rays covered by minute odontodes on free surface. Vertebrae 31(1) to 32(1). Six pairs of ribs (2).

Color in alcohol. Similar to living specimens, with dark background, pale, whitish blotches. Ventral surface light to gray with opaque blotches; in some specimens, ventral surface clearer without any blotch, especially among juveniles.

Color in life. Whole body with dark background, green olive to black, presence of conspicuous yellow spaced spots or blotches ( Fig. 2 ). Blotches can be round, sometimes merged to each other, forming large irregular patterns. Blotches all over head, body, and fins larger and more spaced in juveniles than in adults. During growth, blotches become more rounded and numerous. Ventral surface light brown with pale spaced blotches; sometimes inconspicuous.

Sex dimorphism. Mature males with hypertrophied odontodes on opercle surpassing posterior border of orbit, on distal portion of pectoral spine, and along caudal peduncle. Head of males relatively wider than in females. Mature females wider than males in abdominal area.

Geographical distribution. Scobinancistrus raonii is endemic to the Xingu River basin, restricted to the main channel, immediately downstream of its confluence with the Iriri River up to the Itaobinha region, upstream from Vitória do Xingu ( Fig. 4 ).

Ecological notes. Scobinancistrus raonii inhabits strong, high-energy waters along the main river channel, inhabiting a special microhabitat composed of conglomerate rock formed by gravel, sand, and iron oxide (called “mocororô” by local people). These conglomerates are usually flat rocky plates with spaces and caves carved by the current and can be stacked on the river bottom, giving the tridimensional complexity of this region ( Fig. 5 ). We hypothesize that the yellow blotches along the fish’s body camouflage the fish among the incrusted gravel on the conglomerate. Scobinancistrus raonii is usually found at shallow depths, from 0.5 m to a maximum depth of 11 m. Scobinancistrus raonii is very likely a selective carnivore, such as its congeners, as it feeds on items with its well-developed spatulate teeth ( Fig. 3 ). Analysis of food contents of the other species of Scobinancistrus showed the presence of insects, algae, microcrustaceans and dominance of Porifera (spicula) (Zuanon, 1999; Taís de Jesus, 2020, pers. comm).

Etymology. The new species is named in honor of the Cacique Raoni Metuktire of the Kayapó people. Raoni is one of the most active indigenous leaders in the struggle to preserve the Amazon rainforest and indigenous peoples, being a solid reference for the fight for the conservation of the Xingu River basin for more than 40 years. A patronym.

Conservation status. Scobinancistrus raonii occurs in a limited distribution area, on a stretch of approximately 300 km of the middle Xingu River, Pará State. In an attempt to estimate area of occupancy (AOO – following IUCN, 2022 guidelines) loss, we used the method of 2 x 2 km grid cells to calculate the area between the most distant points in the Xingu River where Scobinancistrus raonii has been registered. The original area before Belo Monte and Pimental dam constructions comprised 1,028 km 2. With the water flow reduction and exposition of rocks of the extensive running waters of the Volta Grande do Xingu (VGX) (ca. 460 km 2) due to the deviation of the main channel of the Xingu River, we can estimate a loss of 45% of the original area. Plus, part of the Xingu River running waters below Altamira city was transformed into a large and deep reservoir by the Pimental dam (220 km 2), causing an additional reduction of 21% of the original area of occupancy of S. raonii . As S. raonii was shown to have restricted habitat requirements (running waters, turbulence, rocky conglomerates), the main impact is the reduction of flow in the reservoir area, which leads to siltation and homogenization of the river bottom ( Fig. 6 ). We are estimating a total loss of AOO of more than 60% of the original area. Approximately more than 95% of the area of occurrence of this species is included in the direct impact area of the Belo Monte Hydroelectric Power Plant, which reduced the natural range of the species due to the environmental degradation of the area. Thus, based in the decline of quality of habitat, area of occupancy (reduced to less than 500 km 2), points of threat (two dams in the area of occurrence, Pimental and Belo Monte, could be considered as locations) and consequently reduction on the population, S. raonii could qualify for the Endangered (EN) category under the IUCN (2022) standards, criterion B2abii,iii, raising many concerns about conservancy of these high-energy water dependent loricariids.

Figures

FIGURE 1 | Lateral, dorsal and ventral views of Scobinancistrus raonii, INPA 59493, holotype, 99.6 mm SL, Senador José Porfírio, Xingu River, ca. 3.5 km downstream from BR-230. Photo: Leandro M. Sousa.

FIGURE 2 | Lateral view of live specimens of Scobinancistrus raonii, Brazil, Pará, Xingu River, Volta Grande do Xingu. Paratypes: INPA 40512, 80.9 mm SL, juvenile (above); LIA 5054, 94.4 mm SL, subadult (middle); ANSP 194989, 120.8 mm SL, adult (below). Photos: Leandro M. Sousa (juvenile and subadult) and Mark H. Sabaj (adult).

FIGURE 3 | Photo in ventral view of the mouth of Scobinancistrus raonii, INPA 40512, paratype, 80.9 mm SL. Photo: Leandro M. Sousa.

FIGURE 4 | Partial map of the Xingu River, showing the distribution of Scobinancistrus raonii (yellow circles). Black circle indicates type locality. Shaded area indicates the Impact Zone of the Belo Monte Dam Complex. Dark blue stretch of the river represents the dammed area. Red stretch indicates the reduced flow impacted area.

FIGURE 5 | Scobinancistrus raonii hiding underneath its preferred microhabitat: conglomerate plates of gravel and iron oxide. Photo: Leandro M. Sousa.

FIGURE 6 | Underwater photography at the exact same locality in Gorgulho da Rita. Above, October 2015, showing a rapids’ habitat with high tridimensional complexity occupied by several species of fish (on the picture: Teleocichla preta, Leporinus tigrinus, Hypomasticus julii). Below, October 2017, same spot after Belo Monte Dam implementation showing that the absence of current promoted siltation and the disappearance of rheophilic species from the area. Photos: Leandro M. Sousa