Hisonotus nigricauda ( Boulenger, 1891 )

Hisonotus nigricauda ( Boulenger, 1891) View in CoL

Figs. 2 View Fig , 3 View Fig , 4a View Fig , 5 View Fig , 6a View Fig , 7a View Fig , and 8a View Fig

Otocinclus nigricauda Boulenger, 1891: 234 [original description, type locality: Rio Grande do Sul, Brazil]. - Regan, 1904: 268-269 [redescription, senior synonym of Hisonotus laevior and Hisonotus leptochilus ]. Fowler, 1940: 83 [listed]. - Isbrücker,1980: 84 [listed].- Schaefer, 1991:23 [phylogenetic relationships of Hypoptopomatinae ].

Hisonotus nigricauda Cope, 1894: 97 [compared with Hisonotus laevior and H. leptochilus and new generic combination]. - Schaefer, 1998: 383 [transferred to Hisonotus ]. - Schaefer, 2003: 232 [listed]. - Reis & Carvalho, 2007: 84 [listed]. - Ferraris, 2007: 248 [listed].

Microlepidogaster nigricauda . - Eigenmann, 1910: 413 [listed]. Miranda Ribeiro, 1911: 88 [listed]. Fowler, 1915: 237 [examined specimen]. - Gosline, 1945: 101 [listed]. - Fowler, 1954: 166-167 [listed and illustrated]. - Malabarba, 1989: 150 [ type locality restricted to laguna dos Patos system, probably rio Camaquã]. - Schaefer, 1997: 8 [listed].

Diagnosis. Hisonotus nigricauda differs from its congeners, except from H. maculipinnis and H. prata , by lacking the posterior portion of the lateral line ( Fig. 4a View Fig ), vs. posterior portion of lateral line present. It differs from H. maculipinnis and H. prata by having an almost completely dark caudal fin, without hyaline areas in the middle portion ( Figs. 2-3 View Fig View Fig ), vs. caudal fin presenting hyaline areas in the middle portion (see remarks for H. maculipinnis diagnosis).

Description. Morphometrics and meristics in Table 1 View Table 1 . Adult size small to medium for members of this genus (less than 40 mm in SL). Body robust, not elongated. Head and body without conspicuous keels. Caudal peduncle round in cross section. Dorsal profile slightly convex from snout tip to dorsalfin origin except slightly concave profile anterior to nares. Straight and posteroventrally sloped at dorsal-fin base, and almost straight from that point to caudal-fin origin. Greatest body depth at dorsal-fin origin. Least body depth at posterior end of caudal peduncle. Posterior profile of caudal-fin margin slightly concave. Head and snout broad, snout rounded to somewhat square in dorsal view, body progressively narrowing posterior to pectoral-fin insertion. Snout region anterior to nares concave, interorbital region slightly convex. Upper margin of orbit somewhat elevate. Eye dorsolaterally positioned. Iris operculum present.

Pectoral fin I,6. Pectoral-fin posterior margin almost straight; when depressed tip extending to middle of pelvic fin. Posterior margin of pectoral-fin spine smooth in adults and juveniles. Pectoral-fin axillary slit present, located below posterior bony margin of cleithral process. Pelvic fin i,5. Tip of depressed pelvic fin not reaching anal-fin origin in females, but extending beyond that point in males. Dorsal fin II,7. Dorsal-fin origin located just posterior of vertical through pelvic-fin origin. Dorsal-fin spinelet somewhat round in shape. Anal fin i,5. First anal-fin pterygiophore exposed anterior to anal fin. Adipose fin absent. Caudal fin i,14,i.

Body almost entirely covered by plates except for region overlying opening of swim bladder capsule, area between pectoral girdle and lower lip, region around anus, and area around base of paired fins. Rostral plate with posterior notch articulation for mesethmoid. Rostral plate thickened, with narrow odontode free band between dorsad and ventrad series of odontodes ( Fig. 5 View Fig ), odontode-free area sometimes absent in smaller specimens. Snout plates anterior to nares reduced, small unplated area between rostrum and nares ( Fig. 6a View Fig ). Two or three rows of predorsal plates (modally three; Fig. 7a View Fig ). Lateral line incomplete, anterior portion short, formed by one to three pored plates. Posterior portion of lateral line absent. Median plate series usually truncated ( Fig. 4a View Fig ). Plates of median abdominal plate series very small, numerous, irregularly arranged. Lateral abdominal plates larger, forming regular series of about four to seven plates on each side ( Fig. 8a View Fig ). Coracoid and cleithrum exposed and covered by odontodes, except for median region of cleithrum between arrector fossae openings and medial region of coracoids.

Head, fin-spines, and body plates covered with odontodes, these larger on anterior surface of all fin spines, medially directed on pelvic fin. Odontodes on head uniform in size and distribution, except for enlarged odontodes on ventral and dorsal margins of rostrum ( Fig. 5 View Fig ). Odontodes on posterior parieto-supraoccipital tip not enlarged, about same size as surrounding areas. Anteroventral margin of compound pterotic with median-to-large size perforations. Infraorbital canal entering infraorbital series via sphenotic. Lips roundish and papillose. Maxillary barbel present.

Premaxillary and dentary teeth slender proximally and flattened distally; bifid, major (medial) cusp large and rounded, minor (lateral) cusp pointed. Accessory patch of teeth absent on dentary and premaxilla.

Compound ventral hypural plate (hypurals 1-2) and compound dorsal hypural plate (hypurals 3-5) not completely fused to each other, median notch on posterior margin of caudal-fin skeleton extending anteriorly. Total vertebrae 27- 28 (4 c&s), one c&s presenting 25 (apparently anomalous).

Color in alcohol. Ground color of dorsal and lateral surfaces gray to almost black. Dorsal and dorsolateral body surfaces slightly lighter than lateral surface, except for head, which is darker. Ventral surface of body heavily pigmented. Area anterior to nares lighter but not forming conspicuous longitudinal light stripes. Paired, dorsal and anal fins mostly hyaline, except for several transverse dark bands. Caudal fin almost completely dark, except for hyaline area on posterior portion of three uppermost branched rays. Caudal-fin hyaline portion, and the unbranched rays with transverse dark bands. Sexual dimorphism. Urogenital papilla positioned just behind the anal opening in males. Adult males also possess a developed fleshy flap along the dorsal margin of first thickened pelvic-fin ray, that is absent in females. Flap slightly wider basally and progressively narrowing distally. In adult males, the first and second branched rays of pelvic fin present a fleshy flap at its anteromedial portion. In juvenile males all flaps are smaller or absent. Males have a longer pelvic-fin unbranched ray that extends beyond the anal-fin origin, with the ray never reaching that point in females.

Distribution and habitat. Hisonotus nigricauda is widely distributed in the laguna dos Patos system and in the rio Uruguay basin. In the laguna dos Patos system that species is found mostly in the lower portions of the tributaries near the laguna do Patos, being absent in the upper portions of rio Jacuí basin. In the same manner, H. nigricauda is most commonly collected in the lower portions of the rio Uruguay basin, but being found in the headwaters of rio Negro, rio Quaraí, and rio Ibicuí drainages ( Fig. 9 View Fig ). Hisonotus nigricauda is apparently absent in the rio Uruguay basin above the mouth of rio Ibicuí. This species inhabits slow flowing watercourses, of brown waters running over dark organic matter and sandy bottom ( Fig. 10c View Fig ). The individuals were found in between marginal and aquatic vegetation.

Remarks. Hisonotus nigricauda is morphologically very similar to Hisonotus maculipinnis (Regan, 1912) from río de La Plata in Argentina; both nominal species being morphometrically identical ( Fig. 11 View Fig ). However, the following features can distinguish them: H. nigricauda has an almost completely dark caudal fin contrasting with a caudal fin with hyaline areas in most specimens of H. maculipinnis (including the type series), especially in juvenile specimens ( Fig. 12 View Fig ). Specimens of H. nigricauda usually posses a narrow odontode-free area between dorsal and ventral series of odontodes on the anterior margin of snout, which is absent in H. maculipinnis specimens. These features putatively distinguish the forms, and both seem to be part of a species complex inhabiting the lower portions of the Paraná-Paraguay and laguna dos Patos systems. Further study, however, is necessary to unambiguously demonstrate that these species are not conspecific, which is beyond the purposes of this work.

Material examined. Brazil, Rio Grande do Sul, laguna dos Patos system : BMNH 91.3.16.53-62 , syntypes of Otocinclus nigricauda , 9, 24.8-31.8 mm SL . Rio Jacuí drainage : ANSP 21565 , 2, 21.3- 22.4 mm SL, rio Jacuí . MCN 16246 , 10, 23.7-34.1 mm SL, Porto Alegre, Parque Estadual Delta do Jacuí , Saco da Pólvora , 30º01’S 51º14’W. GoogleMaps MCP 19834 , 12, 25.6-40.2 mm SL, Amarópolis, creek tributary of rio Jacuí in the sylviculture Santo Amaro , 29º55’S 51º55’W. GoogleMaps MCP 20543 , 1, 31.1 mm SL, Porto Alegre, rio Jacuí on Saco da Alemoa , 30º00’00”S 51º14’51”W GoogleMaps . Rio Caí drainage : MCN 15989 , 3, 27.3-31.7 mm SL, Triunfo, mouth of rio Caí , left margin, 29º55’54”S 51º16’29”W GoogleMaps . Rio Vacacaí drainage : MCP 19584 , 33 + 3 c&s, 22.7- 39.1 mm SL, São Gabriel, bridge on road between São Gabriel and Tiaraju, 30º17’29”S 54º20’18”W. GoogleMaps MCP 26756, 5, 24.2-29.5 mm SL, São Gabriel, marsh of arroio Piraí, 30º17’07”S 54º20’33”W GoogleMaps . Rio Gravataí drainage : MAPA 1737 , 1, 26.7 mm SL, Gravataí, arroio Passo dos Ferreiros , tributary of rio Gravataí , 29º56’S 50º58’W. GoogleMaps MAPA 1759 , 3, 23.5-27.5 mm SL, Canoas, canal south of rio Gravataí . MCP 15059 , 3, 29.4-30.6 mm SL, Gravataí , marsh at highway RS-118, 29º58’S 50º56’W GoogleMaps . Rio dos Sinos : MCN 11625 , 11, 31.3-38.3 mm SL, Sapucaia do Sul, Estação Ecológica do Pesqueiro at Zoológico de Sapucaia do Sul . Lago Guaíba drainage : MAPA 1009 , 2, 11.6-23.9 mm SL, Porto Alegre, lago Guaíba at Medianeira. MCN 17416, 10, 22.0- 32.3 mm SL, Tapes, arroio Guará tributary of arroio Araçá on road between Barra do Ribeiro and Tapes, 30º29’14”S 51º23’39”W. GoogleMaps MCP 21165, 4, 26.8-29.5 mm SL, Eldorado do Sul, creek at margins of highway BR-290, 30º02’36”S 51º20’56”W. GoogleMaps MCP 28986, 11, 24.7- 34.3 mm SL, Eldorado do Sul, arroio Passo dos Carros, 30º05’S 51º23’W GoogleMaps . Laguna dos Patos drainage : MCN 12602 , 4, 16.2-24.8 mm SL, Arambaré, arroio do Brejo , 5 km south of Arambaré on road to Santa Rita do Sul, 30º57’00”S 50º45’26”W. GoogleMaps MCN 12605, 4, 21.6- 27.2 mm SL, Arambaré, arroio Santa Rita at Capão do Trago, 31º01’50”S 51º30’27”W. GoogleMaps MCP 17677, 6, 19.8-24.7 mm SL, Pelotas, old drainage channel near to Passo do Tabajara, marsh of Pontal da Barra in Laranjal, 31º47’S 52º14’W. GoogleMaps MCP 23855, 33, 23.1-34.1 mm SL, Sentinela do Sul, arroio Velhaco on road between Cerro Grande do Sul and Camaquã, 30º41’22”S 51º41’51”W. GoogleMaps MCP 23858, 4, 27.2- 28.9 mm SL, Sentinela do Sul, arroio do Tigre tributary of arroio Velhaco on road from Cerro Grande do Sul to Camaquã, 30º44’30”S 51º46’26”W GoogleMaps . Rio Camaquã drainage : MCP 17416 , 20 + 3 c&s 25.5-39.1 mm SL, Camaquã, marsh in rio Camaquã at Pacheca, 31º08’S 51º47’W. GoogleMaps MCP 19701, 1, 27.2 mm SL, Encruzilhada do Sul, arroio Passo da Miséria on road between Encruzilhada do Sul and Canguçu, 30º57’S 52º26’W. GoogleMaps MCP 25881, 51, 15.8-36.7 mm SL, Caçapava do Sul, creek tributary of arroio Seival on road between Lavras do Sul and Capaçava do Sul, 30º44’00”S 53º42’04”W. GoogleMaps MCP 25875, 1, 34.2 mm SL, Caçapava do Sul, small creek tributary to arroio Hilário on road between Caçapava do Sul and Lavras do Sul, 30º44’24”S 53º44’51”W GoogleMaps . MCP 40761 , 10 + 3 c&s, 31.0- 38.2 mm SL, Bagé, arroio Banhado Grande on highway BR-153 between Bagé and Caçapava do Sul, 31º14’34”S 53º52’50”W. GoogleMaps MCP 44506, 1, 33.2 mm SL, Pinheiro Machado, creek tributary of arroio Boici at Fazenda Chimarrão, 31º14’09”S 53º21’39”W GoogleMaps . Rio São Gonçalo drainage : MCP 17415 , 32, 27.7-34.9 mm SL, Pelotas, dead canal of rio Pelotas , marginal of highway BR-116, at Retiro, 31º37’S 52º20’W. GoogleMaps MCP 17577, 4, 25.1-31.6 mm SL, Pelotas, arroio Totó on road to colônia Z-3, 31º46’S 52º20’W GoogleMaps . Laguna Mirim drainage : MCP 11134 , 2, 28.2- 35.0 mm SL, Arroio Grande, arroio Xasqueiro on highway BR-116 between Pelotas and Arroio Grande, 32º09’S 53º02’W GoogleMaps . From rio Uruguay basin : Rio Ibicuí drainage : MCP 9270 , 10, 17.0- 29.7 mm SL, Mata, creek on road between Santa Maria and Mata, 29º33’S 54º27’W. GoogleMaps MCP 9386, 10, 14.5-24.3 mm SL, Cacequi, rio Ibicuí on bridge between São Rafael and Cacequi, 29º41’S 54º41’W. GoogleMaps MCP 9473, 9, 20.3-32.5 mm SL, Brazil, São Vicente do Sul, arroio do Salso, road from São Vicente do Sul to Santiago, 29º34’S 54º42’W. GoogleMaps MCP 9643 , 33, 22.1-34.1 mm SL, Dom Pedrito, rio Santa Maria at km 246 of highway BR-293, between Dom Pedrito and Santana do Livramento, 30º59’S 54º42’W. GoogleMaps MCP 14145, 1, 24.5 mm SL, Rosário do Sul, creek on road between Rosário do Sul and Santana do Livramento, 30º18’45”S 54º59’49”W. GoogleMaps MCP 14214, 1, 33.2 mm SL, Santana do Livramento, pools at side of rio Santa Maria on road between Dom Pedrito and Santana do Livramento, 30º59’S 54º42’W GoogleMaps . MCP 16161 , 2, 15.5-28.9 mm SL, Santana do Livramento, lateral pools on road to Campo Seco , 15 km east from highway BR-158, 30º42’S 55º04’W. GoogleMaps MCP 19593 , 13, 22.3-33.5 mm SL, São Gabriel, bridge over Banhado do Inhatium , highway BR-290, 30º15’43”S 54º31’33”W. GoogleMaps MCP 23149 , 11, 26.0- 31.4 mm SL, São Francisco de Assis, rio Inhacunda at São Francisco de Assis going to Manoel Viana , 29º32’51”S 55º08’11”W. GoogleMaps MCP 26865 , 88 + 3 c&s, 22.7-38.5 mm SL, Rosário do Sul, arroio do Salso on the highway BR-158, affluent of rio Ibicuí da Armada , 30º22’27”S 55º02’07”W. GoogleMaps MCP 27608 , 14, 16.2-35.9 mm SL, São Francisco de Assis, arroio Caraí-Passo on road from São Francisco de Assis to Manoel Viana , 29º31’03”S 55º10’49”W. GoogleMaps UFRGS 8241 , 23, 23.7-34.5 mm SL, Rosário do Sul, creek at the margin of highway BR-290, 10 km from Rosário do Sul , 30º12’S 55º03’W GoogleMaps . Río Negro drainage : MCP 10000 , 34, 15.4-30.1 mm SL, Uruguay, Cerro Largo, lagoon 10 m from río Negro at Arreria, 31º50’S 54º28’W. GoogleMaps UFRGS 7183 , 17, 29.2-32.5 mm SL, Uruguay, Durazno, arroyo Maestre de Campo , on road to Polanco de Yi , tributary of río Yí , 33º24’55”S 56º12’06”W. GoogleMaps UFRGS 9243 , 7, 29.3-35.5, Uruguay, Rivera, arroyo Batovi on ruta 27, at km 24, río Tacuarembó drainage . UFRGS 9241 , 1, 37.3 mm SL, Uruguay, Rivera, arroyo Cunãpiru on km 12 of ruta 27, río Tacuarémbo drainage , 31º02’21”S 55º29’31”W GoogleMaps . UFRGS 9243 , 5 + 1 c&s, 30.2-36.5 mm SL, Uruguay, Rivera, lateral pools and arroyo Corrales on ruta 27, tributary of río Tacuarembó , 31º23’26”S 55º15’14”W GoogleMaps . Other drainages and rio Uruguay : ILPLA 238 , 9, 18.5-25.8 mm SL, Argentina, Corrientes, arroyo Cuay Grande , 28º41’S 56º14’W. GoogleMaps MAPA 2493 , 15, 23.6-33.6 mm SL, Brazil, Barra do Quarai, arroio Quaraí-Chico , MCP 11568 , 4, 23.2-29.1 mm SL, Brazil, Uruguaiana, rio Touro Passo , 29º38’S 56º56’W. GoogleMaps MCP 16190 , 2, 24.4- 26.2 mm SL, Brazil, São Marcos, marginal lagoon of rio Uruguay at praia da Formosa , 29º30’S 56º49’W. GoogleMaps MCN 16592 , 6, 18.7-33.7 mm SL, Brazil, Itaqui, pool at side of highway BR-472, in marsh drainage canal, Reserva Biológica Estadual de São Donato , 29º00’S 56º10’W. GoogleMaps MCN 16639 , 1, 28.9 mm SL, Brazil, Maçambará, canal at Reserva Biológica Estadual de São Donato , 29º00’S 56º10’W. GoogleMaps MCN 16759 , 7, 18.7-33.7 mm SL, Brazil, Itaqui, creek on highway BR-472 between Itaqui and São Borja, Reserva Biológica Estadual de São Donato , 29º00’S 56º10’W. GoogleMaps