Phenacorhamdia nigrolineata Zarske, 1998

Castro, Íthalo da Silva & Wosiacki, Wolmar Benjamin, 2023, Redescription and expansion of the geographic distribution of Phenacorhamdia nigrolineata (Siluriformes: Heptapteridae), Neotropical Ichthyology (e 220107) 21 (2), pp. 1-19 : 4-14

Phenacorhamdia nigrolineata Zarske, 1998

( Figs. 1–7 ; Tab. 1)

Phenacorhamdia nigrolineata Zarske, 1998:27 (original description). —Bockmann, Guazzelli, 2003:416 (catalog). —Zarske, 2003:23 (list of types). —Ferraris, 2007:189 (catalog). —DoNascimiento, Milani, 2008:165 (comparison). —Maldonado-Ocampo et al., 2008:201 (list of the Colombia). — Barriga, 2012:114 (list of the Ecuador). —DoNascimiento et al., 2017:91 (list of the Colombia). —Rocha et al., 2018:355 (comparison). —Dagosta, de Pinna, 2019:118 (list of the Amazon). —Silva et al., 2022:2 (comparison).

Phenacorhamdia sp. —Bockmann, Slobodian, 2013:54, photo (catalog of the Madeira River).

Diagnosis. Phenacorhamdia nigrolineata is distinguished from congeners, except P. cabocla , P. macarenensis , and P. roxoi , by having a homogeneously dark brown body, without a true, darkly pigmented midlateral stripe (vs. usually light brown in P. anisura , P. boliviana , P. hoehnei , P. taphorni or yellowish in P. somnians , P. suia , P. tenebrosa , P. provenzanoi , and P. tenuis ; P. unifasciata has a longitudinal dark brown stripe along the dorsal half of the body). Additionally, P. nigrolineata differs from all congeners by having a shorter snout (33.2–33.6% vs. 34.3–43.0% HL in P. anisura , P. hoehnei , P. macarenensis , P. roxoi , P. somnians , P. suia , P. taphorni , P. tenebrosa , and P. unifasciata ). In P. nigrolineata the maxillary barbel reaches the end of distal margin of the pectoral fin when adpressed to body (vs. reaching the origin of the pectoral fin in P. cabocla , P. somnians , P. suia , and P. unifasciata ; reaching ¾ of the pectoral fin length in P. anisura ; reaching half the length of pectoral fin in P. tenuis ; reaching the origin of the pelvic fin in P. macarenensis ). The caudal-peduncle depth in P. nigrolineata is 5.3–8.2% SL (vs. 4.3–5.1% SL in P. provenzanoi ). In P. nigrolineata the outer mental barbel reaches the origin of the pectoral fin (vs. not reaching in P. anisura and P. taphorni ). Phenacorhamdia nigrolineata is distinguished from congeners by having 40–41 total vertebrae (vs. 39 in P. taphorni ; 43 in P. boliviana ; 44 in P. cabocla ; 43 or 45 in P. suia ; 45 in P. somnians ; 45 or 46 in P. roxoi ; 46 or 47 in P. unifasciata ; 47 or 48 in P. provenzanoi ; and 53 or 55 in P. tenuis ).

Description. Morphometric data in Tab. 1. Small catfish with elongated body (maximum 47.6 mm SL). Body elliptical in cross section through dorsal-fin origin, progressively more compressed laterally in posterior half. Dorsal profile straight from origin of snout to occipital region, slightly convex from this region to dorsal-fin origin, markedly convex from end of dorsal fin to end of adipose fin base, and straight along caudal peduncle. Ventral profile of head convex, straight along abdomen, then slightly convex at end of anal-fin base and straight along ventral portion of caudal peduncle ( Fig. 1 ).

Head depressed. Snout short, straight in lateral view. Body shallow before dorsal-fin origin and before adipose-fin origin. Mouth prognathous. Anterior and posterior nares forming square in dorsal view. Maxillary barbel moderately long, reaching end of distal margin of pectoral fin when adpressed to body. Outer mental barbel reaching origin of pectoral fin. Inner mental barbel reaching branchiostegal membrane. Eyes small and without free margin, dorsally oriented, and located slightly anterior to medial portion of head.

Pectoral fin rounded with one unbranched and six* (4) branched rays. Simple pectoral-fin ray mostly flexible, except for its basal third, not prolonged by a short filament. Dorsal fin long and rounded with one unbranched and six* (4) branched rays, branched rays gradually shorter. Pelvic fin long and rounded, with one unbranched and five* (4) branched rays, originating slightly anterior to vertical line through origin of dorsal fin. Shallow adipose fin, rectangular, and short, with posterior lobe free and not confluent with caudal fin. Origin of anal fin anterior to origin of adipose fin. Origin of adipose fin vertically aligned to origin of second branched anal-fin ray. Anal fin with one (1) or two* (3) anteriormost rays embedded in thick skin fold, and iv,9*(4) rays ( Figs. 2–3 ).

Caudal fin bifurcated, lobes pointed, ventral lobe slightly longer than dorsal; Dorsal lobe with 13*(3) or 14(1) procurrent rays and one unbranched and five (1) or seven* (3) branched principal rays. Ventral lobe with 13(3) or 15*(1) procurrent rays and one unbranched and eight* (4) branched principal rays.

Osteological characters. In dorsal and ventral views of mesethmoid, anterior edge bifurcates and forms conspicuous cornua ( Fig. 4 ). In dorsal view, central area of posterior edge constitutes anterior margin of anterior cranial fontanel; laterally, posterior edge articulates with frontals. Posterior to cornuas, bone widens and shows lateral projections approximately equal to cornuas, with a mesial process in anterior portion of posteroventral expansion of mesethmoid. Anterior cranial fontanel is elliptical, about one-third of its length extends through mesethmoid, and extending for about 20% of length of neurocranium. Posterior cranial fontanel elongated, elliptical, and extending about one-third of length of neurocranium.

Premaxillary tooth plate retangular-shaped, its distal border slightly wider and without posterior projection. Elongated dental plate, larger than premaxillary plate. Both premaxillary and dentary plates with conical teeth.

Frontal bone connects anterior with mesethmoid and posteriorly to parieto-supraoccipital, defining lateral and posterior border of posterior cranial fontanelle. Frontal form triangle anteriorly. Epiphyseal bar located slightly posteriorly, aligned with posterolateral process of frontal. Parieto-supraoccipital U-shaped in dorsal view, articulating anteriorly with frontal, sphenotic, pterotic and with epiotic posteriorly, and continues posteriorly as process, elongated and pointed, not bifurcate.

Branchial arches with basibranchials 2 and 3 and hypobranchials 1 and 2 ossified. Five ceratobranquials and pharyngobranchials 3 and 4. Four small and conical gill rakers in first ceratobranquial. Seven branchiostegals.

Pre-caudal vertebrae 17*(4) and caudal vertebrae 23(1) or 24*(3), totaling 40(1) or 41*(3) vertebrae. Nine* (4) pleural ribs ( Figs. 2–3 ). First hemal spine at 18 th *(4) vertebrae. Neural spines bifids from vertebrae one to 17*(4), including Weberian complex; neural spine of 13 th vertebra reduced to small spiniform process. Seven* (4) pterygiophores of dorsal fin, first inserted anterior to neural spine of 13 th *(4) vertebra. Anal fin pterygiophores 12(2) or 13*(2); first pterygiophore of anal fin anterior to hemal spine of 22 th * vertebrae; posterior pterygiophores extend to 29 th * vertebrae. Hemal spine bifid between vertebrae 23*(2), 24(1), or 25(1) to 29*(2), 30(1), or 32(1) associated to anal fin pterygiophores ( Figs. 2 , 3 , 5A ). Configuration of neural and hemal spines of the three last caudal vertebrae inclined at 30º in relation to the axis of the vertebral column ( Figs. 2 , 3 , 5B ).

Caudal skeleton formed by ossified parhypural, fused to PU1+U1 complex in anterior portion; hypural 1 and 2 co-ossified as plate, fused to PU1+U1 complex centrum previously; hypural 3 and 4 co-ossified as plate, not fused to PU1+U1 complex centrum and without contact to HU1+HU2; hypural 5 ossified and free, not fused to PU1+U1 complex centrum, without contact with HU3+HU4. Uroneural ossified and fused to PU1+U1 complex centrum ( Figs. 2 , 3 , 5B ).

Laterosensory system. Head with supraorbital pore s1 medially adjacent to anterior nostril, dorsal to cornuas of mesethmoid; s2+i2 halfway between anterior and posterior nares; s3+s4 very close to edge of posterior nares, dorsal to lateral ethmoid; s6 (in the middle of anterior fontanel) absent; s7 absent; s 8 in frontal, posterior to eyes. Infraorbital pore i1 adjacent to anterior nares and opposite to pore s1, next to maxilar; i3 absent; i4 ventral and anterior to ocular border, next to posterior extremity of autopalatine; i5 and i6 pores posterior to eyes ( Fig. 4 ). Preoperculomandibular pores pm1-pm4 located between lower lip and base of mental barbels; pm5 and pm6 just posterior to edge of mouth, and dorsal to base of outer mental barbels, ventral to maxilar; pm7, pm8, pm9 just posterior to base of inner mental barbel. Preopercle with two pores, pm9 and pm10. Postotic pore po1 associated with pm11, forming po1+pm11 complex pore; po2 and po3 dorsally to beginning of opercular membrane. Branch of lateral line originating between po2 and po3, running laterally and posterior to end of head. Conspicuous groove along body, from height of end of pectoral fin retracted to end of caudal peduncle.

Coloration in alcohol. Body homogeneously light brown. Dorsal region of head and occipital region brown. Ventral region pale. Pectoral, dorsal, pelvic, and caudal fin-rays light brown, with inter-radial membranes hyalines. Distal margin of adipose fin hyaline ( Figs. 1 , 6 ). Dark groove or shadow along almost entire length of lateral line of the body.

Coloration in life. Body homogeneously dark brown, with ventral region slightly lighter tone. Fin rays dark brown, with inter-radial membranes hyalines. Base of the adipose fin dark brown ( Fig. 7 ).

Geographical distribution. Phenacorhamdia nigrolineata is distributed across Brazil, Colombia, and Peru (western Amazon basin), and Guyana. Its northernmost record is found in Branco River basin and the easternmost in the middle Tapajós River basin ( Fig. 8 ).

Comparative morphometry. Principal component analysis showed better separation of groups with components 1 and 2 ( Fig. 9 ). The first component retained the highest change (91.2%), followed by the second component (5.6%). In component 1, the population of P. boliviana from the Beni River basin differs from the others (positive loadings, Tab. 2), with the other groups being more similar, while in component 2, the population of P. unifasciata from the Upper Paraná River basin is more distant from the other groups (negative loadings, Tab. 2).

The ANOVA test showed that no significant morphometric differences were found between the evaluated populations of P. nigrolineata of the Amacayacu, Madeira, Tapajós, and Ucayali River basins with the variables analyzed, indicating that these populations may be the same species. However, the same test revealed that the populations of P. boliviana from the Beni River basin and P. unifasciata from the Upper Paraná River basin are significantly different (F = 2.719, df = 55.98, p = 0.02867). When subjected to Dunn's post hoc test, populations of P. boliviana from the Beni River basin showed greater differentiation with populations of P. nigrolineata than with P. unifasciata from the Upper Paraná River basin (p <0.05).

Conservation status. The type locality of the P. nigrolineata , which has suffered from deforestation of native forest cover, mining, and road constructions (Cañas, 2019:147), is outside the area of the nearest national parks such as Cordillera Azul, Sierra del Divisor, Reserva Nacional Tambopata, and El Sira in Peru. The species, hitherto known as endemic to a single location in western Peru (Zarske, 1998), is broadly distributed across the western Amazon basin in relatively little disturbed areas, and it is considerably abundant in some places. Phenacorhamdia nigrolineata should be categorized as Least Concern (LC), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2022).

Ecological notes. Two specimens supposedly belonging to P. nigrolineata were photographed in Peru in April 2017. Both were collected in shallow streams, cloudy and slow, and are not preserved (Steven Grant, 2021, pers. comm.). The first, measuring approximately 10 cm SL was found in a small tributary on the Las Piedras River (12°11’35.7”S 69°09’48.4”W) and the second, approximately 6 cm SL, was found in a tributary of the Gamitana River, both tributaries in the Madre de Dios River basin (12°16’19.2”S 69°04’37.9”W). The adult specimens in aquarium ( Fig. 7 ) have coloration pattern in life and many characteristics compatible with the species P. nigrolineata (Zarske, 1998: fig. 2), although they are larger than the other specimens analyzed up to 47.6 mm SL, including the holotype.

Material examined. Peru: Ucayali River basin: MTD F 20728 , holotype (photo and radiograph), 37.6 mm SL, Ucayali departament, Tierra Roja , Ucayali River, in the road between Campoverde and Tournavista, 08°51’50.6”S 74°48’05.8”W . MTD F 17472 , 1 paratype, 33.2 mm SL (photo and radiograph), MTD F 20739 , 1 paratype, 32.0 mm SL, same data of the holotype . Amazonas River basin: ANSP 179013 , 1 , 19.5 mm SL, Loreto, Itaya River, tributary of the Amazonas River , under the bridge in the highway Iquitos-Nauta , about 25 miles southwest of Iquitos , 04°13’31.2”S 73°28’57.4”W . Brazil: Purus River basin: MCP 35986 , 1 , 22.3 mm SL, Acre, Sena Madureira, Antomari River , between Branco and Sena Madureira Rivers, in the BR-364, 09º29’27”S 68º21’29”W . Madeira River basin: LIRP 10035 , 2 , 34.9 – 39.6 mm SL, Rondônia, São Miguel do Guaporé, Piranhas stream, tributary of the São Miguel River , 11º45’12.5”S 60º40’51.8”W . MCP 35989 , 1 , 24.8 mm SL, Acre, Xapuri, Iná River, tributary of the Xipamanu River , at the rear of Uberaba farm, about 6 km from BR-317, 10°44’13.0”S 68°11’16.0”W . MNRJ 15691 , 1 , 43.1 mm SL (x-ray), Rondônia, Ouro Preto do Oeste, Urupá River, tributary of the Machado River , 10°46’02.2”S 62°07’07.8”W . MZUSP 121769 , 5 , 28.3 – 47.6 mm SL, Rondônia, Manicoré, second stream after the restaurant of the km 150 in the Transamazônica highway, BR-230, towards Apuí , 07°59’00”S 61°41’00”W . Tapajós River basin: MCP 53512 , 14 (1 c&s) 24.6 – 45.8 mm SL, Pará, Itaituba, Itapacurazinho River, Transamazônica road, 04º22’12.9”S 55º50’14.9”W . MCP 53473 , 5 , 25.2 – 42.9 mm SL, Pará, Trairão, tributary of the Taburari River , BR-163, between Trairão and Caracol, 04º53’38.6”S 56º10’43.8”W . MPEG 28510 , 1 , 24.2 mm SL, Pará, Jacareacanga, Vila Rato , 05º13’49.8”S 56º55’22.8”W . Amazonas River basin: MPEG 11750 , 1 , 35.3 mm SL, Amazonas, Coari , tributary of the Tartaruga River , tributary of the Urucu River , 04º53’55.3”S 65º19’18.8”W . MPEG 12195 , 2 , 32.6 – 35.7 mm SL, Amazonas, Coari , IMT stream, Solimões River, 04º49’28.92”S 65º01’50.16”W . Solimões River basin: MPEG 12331 , 2 , 25.5 – 28.4 mm SL, Amazonas, Coari , IMT stream, 04°49’38.6”S 65°01’56.6”W . Colombia: Amazon River basin: IAvH-P 10948, 1 of 5, 45.0 mm SL, Amazonas, Leticia, PNN Amacayacu , 03º00’47.6”S 70º00’01.9”W . Guyana: Branco River basin: AUM 36000 , 24.8 mm SL, Rupununi River , 03°56’02.0”N 59°16’21.1”W .

Figures

FIGURE 1 | Phenacorhamdia nigrolineata, MTD F 20728, holotype, 37.6 mm SL, Peru, Departamento de Ucayali, Tierra Roja, near Pucallpa: A. Dorsal, B. Left lateral, and C. Ventral views. Photographed by Mario Richter.

FIGURE 2 | Radiographic images of Phenacorhamdia nigrolineata, MTD F 20728, holotype, 37.6 mm SL: A. Left lateral and B. Ventral views. Photographed by Mario Richter.

FIGURE 3 | Radiographic images of Phenacorhamdia nigrolineata, MTD F 17472, paratype, 33.2 mm SL: A. Left lateral and B. Ventral views. Photographed by Mario Richter.

FIGURE 4 | Illustration of the cranium of Phenacorhamdia nigrolineata, dorsal view, MCP 53512, 40.0 mm SL. Abbreviations: af, anterior fontanel; AN, antorbital; AP, autopalatine; EP, epioccipital; ES, extrascapula; EX, exoccipital; FR, frontal; i1–6, infraorbital sensory branches 1 to 6; LE, lateral ethmoid; ME, mesethmoid; MX, maxilla; NA, nasal; pf, posterior fontanel; PRE, premaxilla; PT, pterotic; s1–8, supraorbital sensory branches 1 to 8; s2+i2) supraorbital sensory branch 2 + infraorbital sensory branch 2; SP, sphenotic; SOC, supraoccipital; SOCP, supraoccipital process. Scale bars = 1 mm.

FIGURE 5 | Lateral view of caudal vertebrae of Phenacorhamdia nigrolineata, MCP 53512, 40.0 mm SL: A. Hemal spines bifids between vertebrae 24 and 32 (arrows) associated with pterygiophores of the anal fin; B. Posterior vertebrae and caudal skeleton. Abbreviations: EPU, epural; HU1+HU2, ventral hypural plate formed by coossification of hypurals 1 and 2; HU3+HU4, dorsal hypural plate formed by co-ossification of hypurals 3 and 4; HU5, dorsal hypural plate 5; PH, parhypural; PU1+U1, complex centrum composed of preural centrum 1 and ural centrum 1; UR, uroneral. Scale bars = 1 mm.

FIGURE 6 | Phenacorhamdia nigrolineata. A. MTD F 17472, paratype, 33.2 mm SL, Peru, Ucayali departament, Tierra Roja, Ucayali River basin (Photographed by Mario Richter). B. IAvH-P 10948, 45.0 mm SL, Colombia, Amazonas River basin, Leticia, PNN Amacayacu (Photographed by Juan Gabriel A. Garzón). C. MCP 53512, 40.0 mm SL, Brazil, Tapajós River basin, Itapacurazinho river. D. AUM 36000, 24.8 mm SL, Guyana, Rupununi River, tributary of the Branco River basin (Photographed by Jonathan Armbruster). Scale bars = 1 cm.

FIGURE 7 | Unpreserved aquarium specimen supposedly of Phenacorhamdia nigrolineata (approximately 60 mm SL) from Madre de Dios River basin, Peru, showing its color in life. Photographed by Steven Grant.

FIGURE 8 | Geographical distribution of Phenacorhamdia nigrolineata in the western Amazon basin. Black star represents the type locality in Peru; black dots represent remaining known localities. One dot may represent more than one lot.

FIGURE 9 | Dispersion of individual scores of first two principal component analysis of four populations of Phenacorhamdia nigrolineata (blue dots = Ucayali River basin; brown dots = Amayacu River basin; green dots = Madeira River basin; black dots = Tapajós River basin), P. boliviana (gray dots = Beni River basin), and P. unifasciata (purple dots = Upper Paraná River basin).