Hypancistrus yudja, Sousa & Sousa & Ribeiro & Sabaj & Zuanon & Py-Daniel, 2025

Hypancistrus yudja , new species

urn:lsid:zoobank.org:act:

( Figs. 1–2 View FIGURE 1 View FIGURE 2 ; Tab. 1 View TABLE 1 )

Hypancistrus L174. — Stawikowski, 1994:536 (aquarium fish atlas; citation and brief description). — Schraml, Schäfer, 2004:134 (aquarium fish atlas). — Seidel, Evers, 2005:588–90 (book; citation and brief description). — Seidel, 2008:112 (book, citation and brief description). — Camargo et al., 2013:173–81 (book, ornamental fish).

Hypancistrus sp. 2 . — Camargo et al., 2013:185 (book, ornamental fish). — Ramos et al., 2015:97 (citation).

Hypancistrus View in CoL sp. nov. — Lees et al., 2016:460–61 (citation and pictured).

Holotype. INPA-ICT 61049 , 42.1 mm SL, rio Xingu , main channel along right bank at Pimental Dam site, ca. 37 km southeast of Altamira, Pará State, Brazil, 03°25’55.3”S 51°57’23.6”W, 11 Nov 2014, M. H. Sabaj, L. M. Sousa, A. P. Gonçalves, D. B. Fitzgerald, V. Machado, P. M. Ito, A. Oliveira, H. Gimênes Jr., M. Hardman, J. Tiemann, K. S. Cummings, M. C. Dreher Mansur and ornamental fishermen. GoogleMaps

Paratypes. All specimens from Xingu , Brazil, Pará State: ANSP 193084 About ANSP , 5, not measured, rio Xingu , deep rocky ledges in main channel, ca. 60 km east-southeast of Altamira, 03°24’58.5”S 51°42’38.6”W, 14 Oct 2012, M. H. Sabaj & L.M. Sousa. GoogleMaps ANSP 194887 About ANSP , 10, 31.8–49.4 mm SL, rio Xingu ( lower Volta Grande ), main straight channel running from south-southwest to north-northeast, 03°11’3.36”S 51°37’2.46”W, 28 Sep 2013, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. Madoka Ito & fishermen. GoogleMaps ANSP 197292 About ANSP , 1, 42.3 mm SL, collected with the holotype; GoogleMaps ANSP 197623 About ANSP , 3, 29.8–44.1 mm SL, GoogleMaps LIA 5070 View Materials , 2, 47.4–48.0 mm SL, rio Xingu , central channel, 03°24’58.5”S 51°42’38.7”W, 9 Nov 2014, M. H. Sabaj & L. M. Sousa. GoogleMaps ANSP 198631 About ANSP , 1, 41.5 mm SL, GoogleMaps LIA 5059 View Materials , 1, 44.9 mm SL, rio Xingu , major channel just upstream of cachoeira do Jericoá , ca. 55 km east-southeast of Altamira, 03°22’55.4”S 51°44’13.0”W, 8 Nov 2014, M. H. Sabaj & L. M. Sousa. GoogleMaps ANSP 198636 About ANSP , 2, 28.0– 32.1 mm SL, rio Xingu , major channel along right bank, ca. 60 km southeast of Altamira, 03°31’06.2”S 51°45’08.1”W, 9 Nov 2014, M. H. Sabaj & L. M. Sousa. GoogleMaps AUM 74485 View Materials , 2, 44.5–45.7 mm SL, collected with ANSP 194887. GoogleMaps INPA-ICT 30115 , 10, 30.8–34.0 mm SL, Belo Monte , 03°06’54”S 51°43’15”W, 5 Nov 2004, L. M. Sousa & E. D. Ribeiro. GoogleMaps INPA-ICT 31404 , 19, 26.7–42.8 mm SL, Maia Community, rocky outcrop in front of the camp, 03°30’44”S 51°44’43”W, 9 Nov 2008, M. Santos, L. Rapp Py-Daniel, I. M. Soares, R. P. Ota, D. B. Fitzgerald, A. P. Gonçalves, L. M. Sousa & M. Sabaj-Péres. GoogleMaps INPA-ICT 40757 , 15, 30.8–51.1 mm SL, rio Xingu , below Volta Grande, narrow region of the main channel, 03°11’03”S 51°37’02”W, 28 Sep 2013, A. R. Martins, D. R. G. Ribeiro, R. R. Reyes, D. B. Fitzgerald, J. Zuanon, M. Arce, A. P. Gonçalves & M. Sabaj-Péres. GoogleMaps INPA-ICT 43790 , 6, 27.0– 41.5 mm SL, deep rocky ledges in main channel, ca. 60 km east-southeast of Altamira, 03°24’58.5”S 51°42’38.6”W, 14 Oct 2012, L. M. Sousa, D. Fitzgerald, A. S. Oliveira, P. M. Ito, N. Lujan, R. Robles, V. Vargas & M. Sabaj-Péres. GoogleMaps INPA-ICT 47294 , 3, 29.6–49.0 mm SL, rio Xingu , main channel on the right bank, ca. 60 km from Altamira, 03°31’06”S 51°45’08”W, 9 Nov 2014, L. M. Sousa, D. Fitzgerald, A. S. Oliveira, P. M. Ito, N. Lujan, R. Robles, V. Vargas & M. Sabaj-Péres. GoogleMaps INPA-ICT 47526 , 1, 31.1 mm SL, Rio Xingu , ca. 4.5 km above Praia do Caju, 03°24’58”S 51°42’39”W, 9 Nov 2014, L. M. Sousa, D. Fitzgerald, A. S. Oliveira, P. M. Ito, N. Lujan, R. Robles, V. Vargas & M. Sabaj-Péres. GoogleMaps INPA-ICT 52316 , 6, 31.5–46.7 mm SL, rio Xingu , Praia do Caju, 03°22’58”S 51°44’17”W, 2 Sep 2012, IBAMA. GoogleMaps LIA 1680 , 9, 31.1–48.0 mm SL, Pedral do Jaú, 03°38’12.1”S 51°73’67.8”W, 10 Nov 2013, A. Gonçalves & L. M. Sousa. GoogleMaps LIA 1685 View Materials , 4, 33.5–50 mm SL, region of Jericoá, 03°41’56.3”S 51°71’10.5”W, 10 Nov 2013, A. Gonçalves & L. M. Sousa. GoogleMaps LIA 5076 View Materials , 1, 28.6 mm SL, collected with ANSP 198636. GoogleMaps LIA 6956 View Materials , 1, 28.1 mm SL, region of Jericoá, 03°24’59”S 51°42’38”W, 3 Oct 2017, L. M. Sousa. GoogleMaps LIA 6938 View Materials , 4, 26.7–39.6 mm SL, Largo do Maia , 03°31’05”S 51°45’07”W, 4 Oct 2017, L. M. Sousa. GoogleMaps LIA 6944 View Materials , 3, 23.0– 42.8 mm SL, region of Jericoá, 03°22’53”S 51°44’13”W, 3 Oct 2017, L. M. Sousa. GoogleMaps ROM 112318 About ROM , 3, 40.1–44.9 mm SL, collected with ANSP 194887 GoogleMaps .

Diagnosis. Hypancistrus yudja can be distinguished from all congeners by its unique color pattern consisting of body with a light tan background and relatively large brown blotches and saddles ( vs. pattern composed of small, dark, isolated spots in H. phantasma ; background color dark brown to black with pale spots in H. contradens , H. inspector , H. lunaorum , H. margaritatus , and H. vandragti or with pattern of pale lines and small spots in H. debilittera Armbruster, Lujan & Taphorn, 2007 ; coloration composed of alternating dark and pale wavy lines that are broad in H. furunculus and narrow in H. seideli ; and background white with roughly straight black stripes in H. zebra ).

Description. Morphometric and meristic data in Tab. 1 View TABLE 1 . Small-sized loricariid, with largest examined specimen measuring 50.0 mm SL. Body short and deep, deepest point at insertion of dorsal fin (19–27% SL), becoming gradually slender after dorsal-fin base. In lateral view, dorsal profile gently convex from snout to dorsal-fin insertion and gently declining from this point to end of caudal peduncle; peduncle concave from end of adipose fin to last lateral plate (11–18% SL). Ventral profile straight from snout tip to pelvic-fin insertion, then ascending gently to insertion of first caudal-fin ray. Greatest width of body at cleithrum (30-37% SL). Head somewhat long (35-41%), without ridges or carinae. Head and snout completely covered by plates supporting odontodes. Cheek odontodes completely exposed and set in depression anterodorsally to cleithrum. Eye laterodorsal with small but conspicuous iris; orbit round and slightly elevated, dorsal rim of orbit barely reaching level of dorsalmost portion of frontal bones.

Interorbital almost flat between orbital ridges. Parieto-supraoccipital process showing conspicuous crest and pointed posteriorly. Parieto-supraoccipital limited posteriorly by set of predorsal plates arranged as one disjunct pair, followed by one or two closely attached pairs plus one single plate immediately anterior to dorsal-fin. Oral disk circular, lips almost completely covered with small round papillae (papillae larger on proximal region of lower lip), margin of lower lip smooth (papillae absent). Lower lip large but not reaching pectoral girdle. Maxillary barbel moderate in size, longer than orbital diameter, almost reaching tip of cheek plates, with large portion free from lower lip. Premaxillary teeth thin, delicate and bifurcated; mesial cusp larger, lateral cusp reaching mid portion of mesial cusp; teeth somewhat numerous (4–14), two to three times smaller than dentary teeth; tooth crown bright red. Dentary with fewer teeth than premaxillary (1–7), similar in shape but considerably larger than premaxillary ones. Dentary tooth rows arranged in approx. 90°angle. Branchial opening small. Interbranchial distance 17–29% HL.

Lateral line plates 20 to 24 (21*), three to five (4*) plates between dorsal and adipose fin, eight to 10* plates between anal and caudal fin. Body plates not carinate or keeled. Caudal peduncle deep and covered by five series of plates. All body plates covered by strong odontodes. Ventral surface entirely naked from snout to anal-fin insertion; single plate between urogenital opening and anal-fin insertion. All fin rays supporting odontodes, more developed on first (undivided) ray. Dorsal fin II+7*, pectoral fin I+5–6 (modally 6*), pelvic fin i+4–5 (modally 5*), anal fin I+3–4 (modally 4*) and caudal fin i+13–14+i (modally 14* branched rays). Dorsal fin spinelet triangular, with functional locking mechanism. Dorsal fin reaching adipose fin when adpressed. Adipose fin slanted posteroventrally, spine strong, straight to gently curved with pointed tip reaching first caudal-fin procurrent ray; base containing five plates; preadipose plate present.

Tip of adpressed pectoral fin reaching one-third of pelvic-fin length; adpressed pelvic fin slightly surpassing posterior end of anal-fin base; paired fins triangular with slightly curved posterior margin. Caudal fin lunate with the upper lobe slightly smaller than lower lobe.

Color in alcohol. Overall background color pale white or cream; irregular brown to dark-brown rounded or elongated blotches along head, body and fins ( Figs. 1–2 View FIGURE 1 View FIGURE 2 ). Ventral surface uniformly light, beige, with little or no pigmentation. Brown blotches sometimes coalesce to form saddles, dumbbells or other irregular shapes. When present, dorsal saddles usually not bilaterally symmetrical. Area between and just past dorsal posterior margin of orbits often with broad dark transverse bar; longitudinal dark oblique bars often present from orbit and nares, respectively, to ventral lateral margin of snout. All fin rays with two to three dark markings that can be organized as stripes. Some specimens showing wide dark transversal bars on dorsal fin.

Color in life. Similar to preserved specimens but contrast between pale background and dark brown blotches more evident (description based on observations of several specimens in aquarium, on pictures of living specimens and in freshly collected specimens).

Sexual dimorphism. Hypancistrus yudja presents the secondary sex characteristics often seen in ancistrin loricariids. Mature males possess hypertrophied odontodes on the cheek, pectoral spine and most of the body plates. Odontodes on body plates become larger on the caudal peduncle. Based on observations of aquarium-kept specimens, the hypertrophied odontodes on mature males appear to be permanent. The head slightly longer and wider in males than in females. Gravid females are usually distinguishable in dorsal view due to their wider abdominal region. Males seem to grow a little larger than females.

Geographical distribution. Hypancistrus yudja is only known from a very small stretch of the Volta Grande do Xingu, spanning nearly 75 km of the main river course ( Fig. 3 View FIGURE 3 ).

Ecological notes. Hypancistrus yudja inhabits deep portions of the rio Xingu channel. It was only found hidden in lateritic conglomerates below 15 m of depth ( Fig. 4 View FIGURE 4 ). All specimens were collected individually by hand during diving sessions aided by air compressors or scuba equipment. Observations made on specimens kept in captivity suggest that it is a fairly shy species that remains secluded in caves for most of the day. Expert aquarium hobbyists have successfully bred this species. The female lays around 15– 20 eggs in a cave that is protected by the male. The fry grows slowly in captivity, often taking two years or more to reach maturity. Under prime conditions they will reach 4–5 cm TL in about a year.

Popular name. Acari-zebra-marrom, zebra-marrom, acari-marrom (in Portuguese); Ozelot-Harnischwels (in German); Ozelot pleco, false zebra pleco, Peruvian (sic) Panther pleco (in English); L174 (L code number).

Etymology. Named after the Yudjá (also known as Juruna), a group of indigenous people from Volta Grande do Xingu. In the Tupi language, Yudjá means “the river owners”. This ethnic group has an intimate relationship with the Xingu, being pioneers in navigation on the turbulent, rocky-bottomed waters of this river. Hypancistrus yudja is restricted to the Yudjá territory and was a source of income for the indigenous ornamental fishermen who dove below 15 m to catch specimens for the aquarium trade. Both the Yudjá people and H. yudja are struggling to survive the environmental impacts of the Belo Monte Hydroelectric Complex on Volta Grande do Xingu, and their fate is connected and deeply threatened.

Conservation status. Hypancistrus yudja is restricted to a 75 km stretch of the Volta Grande region of the rio Xingu, in the state of Pará, Brazil. The species’ entire area of occurrence falls within the direct impact zone of the Belo Monte Hydroelectric Complex, placing it at high risk of extinction due to severe environmental degradation. This species can be classified as Critically Endangered (CR) under IUCN criteria A4a,c,d, (IUCN, 2022) due to an estimated population decline exceeding 80%, driven by severe habitat degradation from the diversion of over 70% of the rio Xingu’s water for hydroelectric operations, disruptions to natural flood and drought cycles, and exploitation for the ornamental fish trade. Recent scuba surveys failed to locate the species in its known habitat, further suggesting a drastic population decline.