Gymnogeophagus mekinos, Malabarba & Malabarba & Reis, 2015

Malabarba, Luiz R., Malabarba, Maria Claudia & Reis, Roberto E., 2015, Descriptions of five new species of the Neotropical cichlid genus Gymnogeophagus Miranda Ribeiro, 1918 (Teleostei: Cichliformes) from the rio Uruguay drainage, Neotropical Ichthyology (Neotrop. Ichthyol.) 13 (4), pp. 637-662 : 644-647

Gymnogeophagus mekinos , new species u r n:l sid:z o ob a n k.o r g:a c t: 142A A 25B -2A11- 4770 -AC 4C - 7CDA383ED842

Figs. 6b , 8

Gymnogeophagus sp. A . - Wimberger et al., 1998 (molecular phylogeny).

Gymnogeophagus cf. gymnogenys complex - Clade 1 - Pereyra & García, 2008 (molecular phylogeny).

Gymnogeophagus aff. gymnogenys . - Serra et al., 2014 (photo; distribution).

Holotype. MCP 19296 , male, 92.4 mm SL, Brazil, Rio Grande do Sul, rio Piraizinho, on road from Bagé to Dom Pedrito , tributary of rio Negro , approximately 31°06’S 54°07’W, 9 Dec 1992, J. P. Silva, R. E. Reis, P. H. Wimberger & C. S. Fontana.

Paratypes. Brazil: Rio Grande do Sul: MCP 16119 (25, 38.3-98.8 mm SL), UMMZ 225495 (10, 49-95 mm SL), collected with the holotype. MAPA 2190 (7, 55.0- 104.5 mm SL), rio Negro, on road from Bagé to Dom Pedrito, approx. 31°08’S 54°22’W. MCP 9023 (24, 46.3-79.8 mm SL), ZVCP 12958 (2, 57.7-78.9 mm SL), upper rio Negro on road from Bagé to Aceguá , Bagé , approx. 31°21’S 54°03’W, 25 Oct 1982, C. A. Lucena & L. R. Malabarba. UFRGS 8396 (162, 23.0- 104.1 mm SL), rio Negro on road BR-153 between Bagé and Aceguá, Bagé, 31°28’37’’S 54°08’20’’W, 29 Mar 2006, L. R. Malabarba and students . Uruguay: UFRGS 7402 (26, 25.7-107.8 mm SL), arroyo Batovi on Ruta 5, 20 km from Tacuarembó, río Negro basin, Tacuarembó, 31°54’30’’S 56°01’14’’W, 28 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera .

Additional non-type specimens. Brazil: Rio Grande do Sul: UFRGS 7146 (136), rio Negro , on road BR-153 between Bagé and Aceguá, Bagé, 31°36’53’’S 54°08’19’’W, 29 Mar 2006 . UFRGS 8395 (6), arroio Cinco Salsos, tributary of rio Negro, on road BR-153 between Bagé and Aceguá , Bagé , 30°28’37’’S 54°08’42’’W, 29 Mar 2006 . UFRGS 8397 (193), arroio Piraí, tributary of rio Negro, on road BR-293 between Bagé and Dom Pedrito , Bagé , 31°13’12’’S 54°16’30’’W, 30 Mar 2006 . Uruguay: Rivera: UFRGS 7242 (109 alc), arroyo Corrales and lateral ponds on Ruta 27 , río Negro basin, 31°23’26’’S 55°15’14’’W, 27 May 2005 . UFRGS 7283 (3) , río Negro, on Ruta 44, Paso de Mazangano, to Ruta 26, 32°06’33’’S 54°40’05’’W, 27 May 2005 . UFRGS 7471 (79), arroyo Cuñapiru, km 12.3 of Ruta 27 , río Negro basin, 31°02’21’’S 55°29’31’’W, 27 May 2005 . UFRGS 7472 (75), arroyo Yaguari on Ruta 17 , río Negro basin, 31°35’55’’S 54°59’19’’W, 27 May 2005 . Tacuarembó: UFRGS 7331 (136), río Tacuarembó on Ruta 26 in Villa Ansina , río Negro basin, 31°58’33’’S 55°28’13’’W, 28 May 2005 . UFRGS 7358 (84), río Caraguatá , tributary of río Tacuarembó on Ruta 36 in Las Toscas , río Negro basin, 32°09’29’’S 55°01’27’’W, 28 May 2005 . Durazno: UFRGS 7371 (30) rio Yi on road to San Borja , río Negro basin, 33°23’49’’S 56°24’10’’W, 29 May 2005 . UFRGS 7394 (32) stream tributary to arroyo Maestro de Campo, on the way to Polanco de Yi, tributary of río Yi , río Negro basin, approx. 33°23’S 56°13’18’’W, 25 May 2005 . UFRGS 7469 (9) río Yi on the city camp , río Negro basin, 33°21’45’’S 56°31’12’’W, 29 May 2005 . UFRGS 9434 (2) rio Yi on road to San Borja , río Negro basin, 33°23’49’’S 56°24’10’’W, 29 May 2005 .

Diagnosis. Gymnogeophagus mekinos can be distinguished from all congeners, except G. gymnogenys , by the possession of a conspicuous and oblique dark band from the eye to the anterior border of the head in adult males ( Fig. 8a ). Gymnogeophagus mekinos can be distinguished from G. gymnogenys by the more elongate body (body depth 34.9- 38.3% SL, mean = 36.7 vs. 38.6-44.2 % SL, mean = 40.6 in G. gymnogenys in specimens larger than 65 mm SL), and by the continuous iridescent olivaceous coloration of males vs. the presence of clearly demarcated iridescent blue spots on the center of each scale in G. gymnogenys .

Description. Morphometric data summarized in Table 2. Body elongated and laterally compressed. Dorsal profile of head approximately straight or slightly convex between mouth and interorbital area and convex from interorbital region to dorsal-fin origin. Predorsal body profile modified in adult males which may show small adipose hump ( Fig. 8a, b ). Dorsal-fin base slightly convex. Caudal peduncle longer than deep, with dorsal and ventral profile slightly concave.

Snout pointed, straight or slightly convex dorsally and ventrally in lateral aspect; narrow and anteriorly rounded in dorsal aspect. Eye small, close to dorsal profile of head in juveniles and progressively farther in larger specimens; eye slightly posterior or near middle of head length. Interorbital area convex, more strongly so in larger specimens; interorbital width smaller than eye diameter in young (up to 70 mm SL) and progressively larger than eye diameter in larger specimens. Posterior tip of maxilla not reaching vertical line across anterior margin of eye. Upper jaw slightly longer than lower jaw.

Body scales large and ctenoid, smaller around pectoral fins; scales ctenoid even in preventral area. Caudal fin with single series of small ctenoid and elongate scales between contiguous rays reaching about half length of fin in both upper and lower lobes. Other unpaired fins without scales. Cheek scales cycloid in 2 or 3 rows; cheek naked anteroventrally. Most of opercle scaled; one vertical row of ctenoid scales on its anterior margin. Subopercular scales ctenoid in single row. Upper lateral line 15(1), 16(5), 17*(7), 18(5), 19(3); lower lateral line 7(1), 9(3), 10*(4), 11(8), 12(1), 13(4), usually with 1 or 2 small perforated scales continuing onto caudal-fin base. Scales between upper lateral line and dorsal fin 4*(18) or 5(3). Scales between upper lateral line and anal fin 8*(12), 9(9). E1 scales 26(2), 27(8), 28*(11).

Dorsal-fin spines 13(6), 14*(13), 15(2); dorsal-fin soft rays 9(2), 10*(14), 11(5). First dorsal-fin spine inserted at vertical line across or slightly posterior to posterior bony margin of opercle. Soft dorsal fin in young and females rounded, reaching to or almost reaching caudal-fin base. Soft dorsal fin pointed in mature males, with 3rd and 4th or 4th and 5th ray produced and reaching proximal third to almost end of caudal fin. Anal-fin with three spines and 8(12), 9*(5) or 10(1) soft rays. Anal-fin origin slightly posterior to last dorsal-fin spine; soft portion nearly rounded in young and females and clearly pointed in males. Pectoral fin pointed, more strongly so in adults; 3rd and 4th rays longest, passing vertical across anal-fin origin. Pelvic fin pointed, more conspicuously in adult males; 2nd soft ray longest, reaching anal opening or region between anal opening and anal-fin origin in young and females, and passing anal-fin origin in adult males. Caudal-fin margin concave, upper lobe longest.

Jaw teeth small, conical, with slightly recurved tips. Upper jaw with outer regular row of nearly 20 teeth in each premaxilla (number increasing with specimen size) and an irregular inner tooth band of slightly smaller teeth. Lower jaw with tooth band arranged in 3-4 irregular rows. Lower limb of first gill arch with 6-7 gill rakers; upper limb lobed, with 4-5 gill rakers on its margin.

Lower pharyngeal tooth plate slightly wider than long; length of bone 94% of width; dentigerous area covering whole occlusion surface; 21 teeth in posterior row, 17 on median row. Posterolateral teeth unicuspid, very thin with slightly recurved tips, becoming progressively smaller caudally; posteromedial teeth much larger, molariform, unicuspid, with medial cusps slightly curved anteriorly ( Fig. 6b ).

Vertebrae 13+15(1), 13+16(2) in three cleared and stained specimens.

9023) are from the rio Negro. Ranges include holotype .

Color in alcohol. Mature males ( Fig. 8a ): ground color of body light yellow, darker above longitudinal series of scales bearing lower lateral line. Vertical bars not clearly discernible. Midlateral spot not well defined, on scales 9-10 of scales row below upper lateral line and on scales 8-10 of scales row above lower lateral line. Dark band in front of dorsal-fin origin, extending ventrally and slightly posteriorly, reaching first scales of upper lateral line, and extending anteriorly through dorsal head profile. Head light brown, with black markings below eye in small males, usually not seen in larger males. Presence of conspicuous and oblique dark band from eye to anterior border of head in adult males; inconspicuous vertical dark band covering cheek, most clearly seen in small males. Isthmus and branchiostegal membrane light brown. Pectoral fin hyaline. Pelvic fin dark brown. Spinous portion of dorsal fin faint brown, usually without markings; soft portion faint brown covered with numerous small circular white spots. Distal length of anal fin spines and rays dark brown, without additional distinct marks. Proximal third of anal-fin rays covered with very small and conspicuous white dots. Caudal fin faint brown with circular white dots along its half proximal length.

Ground color in females and young light yellow. Midlateral spot as described for males. Dark band in front of dorsal-fin origin, extending ventrally and slightly posteriorly, reaching first scales of upper lateral line, but not extending anteriorly through dorsal head profile as described for males. Head yellowish brown, sometimes with black markings below eye. Conspicuous vertical dark band covering cheek. Vertical bars conspicuous in small specimens, distributed from pectoral-fin insertion to caudal peduncle. Vertical bars variable in shape. Isthmus and branchiostegal membrane light yellow. Pectoral and pelvic fins hyaline. Dorsal fin faint brown; soft portion with small white spots. Proximal half of anal and caudal fins covered with small, circular, white spots.

Color in life. Ground color of laterodorsal region of body in males ( Fig. 8b ) mainly olivaceous with vertical black indistinct bars from pectoral-fin insertion to caudal fin base. Body ventrally bright yellow; pale yellow to white along prepelvic region. Head largely yellowish gray, lower lip and jaw white. Adipose hump also brown, but darker than head. Head with small light dots posteriorly to eye, and on opercle. Dark band on dorsal fin origin extending posteroventrally to upper lateral line scales. Spiny portion of dorsal fin dark yellow with short white stripes; soft portion faint red covered with light roundish spots. Caudal fin olivaceous at base and faint red at distal portion; all covered with light roundish spots. Anal fin faint red with light roundish spots on proximal third; distal portion of rays dusky. Pectoral fins hyaline, and pelvic fins darkly pigmented.

Color in life of females ( Fig. 8c ) similar to that described for males, but paler. Body coloration pale brown instead of olivaceous and yellow as in males. Most conspicuous difference refers to darker color of head with more numerous light dots distributed over cheek, opercle and surrounding eye. Some body scale series with bright blue spots.

Distribution. Gymnogeophagus mekinos inhabits the río Negro, connected to the lower río Uruguay ( Fig. 1 ). Pereyra & García (2008) have identified specimens belonging to their Clade 1 (recognized herein as G. mekinos ) from the río Tacuarí and río Yaguarón (rio Jaguarão in Brazil) basins, both tributaries of the lagoa Mirim, laguna dos Patos drainage. The presence of freshwater fish species from the río Negro drainage in the río Tacuarí and río Yaguarón drainages has been previously reported by Loureiro et al. (2011), which also describe a characteristic elbow of capture involving the río Tacuarí and the río Negro. Although we have not examined those specimens sequenced by Pereyra & García (2008), the presence of G. mekinos in the río Tacuarí / lagoa Mirim drainage is probable based on their DNA analysis.

Etymology. From the Greek mekinos meaning prolonged, in reference to the comparatively elongated body of this species. A noun in apposition.

Conservation status. Gymnogeophagus mekinos is relatively frequent and abundant in the rio Negro basin. The Extent of Occurrence (EOO) is approximately 23,300 square kilometers and no specific threats were detected, and the species can be categorized as Least Concern (LC) according to IUCN criteria ( IUCN, 2014).

Figures

Fig. 6. Lower pharyngeal tooth plates in occlusal view: a, G. pseudolabiatus, MCP 11228, 71.6 mm SL; b, G. mekinos, MCP 11251, 84.2 mm SL; c, G. constellatus, MCP 10827, 91.4 mm SL; d, G. missioneiro, MCP 12725, 59.3 mm SL; e, G. lipokarenos, MCP 12991, 89 mm SL. Scale bars = 1 mm.

Fig. 8. Gymnogeophagus mekinos: top, holotype, male, MCP 19296, 92.4 mm SL, rio Piraizinho, on the road from Bagé to Dom Pedrito, tributary of rio Negro, Rio Grande do Sul, Brazil; middle, paratype, male, UMMZ 225495, 94.5 mm SL, collected with the holotype; bottom, paratype, female, UFRGS 7402, 77.5 mm SL, arroio Batovi na rota 5 à 20 km de Tacuarembó, no km 365,6, drenagem do rio Tacuarembó, bacia do rio Negro, Tacuarembó, Uruguay.

Fig. 1. Rio Uruguay and adjacent drainages showing the distribution of the examined specimens of Gymnogeophagus lipokarenos (dark blue), G. missioneiro (light blue), G. constellatus (red), G. pseudolabiatus (orange), and G. mekinos (yellow). Stars represent the type localities.