Astyanax courensis, Bertaco & Carvalho & Jerep, 2010

Bertaco, Vinicius A., Carvalho, Fernando R. & Jerep, Fernando C., 2010, Astyanax goyanensis (Miranda-Ribeiro, 1944), new combination and Astyanax courensis, new species (Ostariophysi: Characiformes): two Characidae from the upper rio Tocantins basin, Central Brazil, Neotropical Ichthyology 8 (2), pp. 265-275 : 269-272

Astyanax courensis , new species

Figs. 5-6

Holotype. UFRGS 11499 , 54.2 mm SL, female, rio dos Couros at Parque Portal da Chapada , tributary of rio Tocantinzinho, upper rio Tocantins basin, 1135 m a.s.l, Alto Paraíso de Goiás, Goiás State, Brazil, 14º09’58”S 47º35’43”W, 10 Sep 2009, V. A. Bertaco, F. R. Carvalho & G. Frainer.

Paratypes. Alto Paraíso de Goiás, Goiás State, Brazil, upper rio Tocantins basin, rio dos Couros basin. MCP 44403, 20 , 26.0- 59.2 mm SL, UFRGS 11290 , 107 , 5 c&s, 16.6-71.6 mm SL, UFRGS 11295 , 5 (ethyl alcohol anhydrous), 23.4-29.5 mm SL, collected with the holotype. MCP 44404, 1 , 44.0 mm SL, córrego Capão da Guabiroba , tributary of rio dos Couros, 14º07’43”S 47º38’27”W, 4 Aug 1996, W. R. Koch, P. Milani & K. M. Grosser. UFRGS 9934 , 5 , 21.1-36.4 mm SL, córrego on road GO-239 between Alto Paraíso de Goiás and Parque Nacional da Chapada dos Veadeiros, 14º08’24”S 47º39’36”W, 25 May 2008, F. C. Jerep & T. P. Carvalho. UFRGS 11588 , 38 , 2 c&s, 18.7-48.2 mm SL, rio das Cobras between Alto Paraíso de Goiás and Parque Nacional da Chapada dos Veadeiros, 14º09’39”S 47º37’55”W, 25 May 2008, F. C. Jerep & T. P. Carvalho .

Diagnosis. Astyanax courensis belongs to the A. scabripinnis species complex and is distinguished from other species of this complex by the number of scale rows between lateral line and pelvic fin origin (3-4 vs. 5-6), except from A. brachypterygium , A. burgerai Zanata & Camelier, A. goyanensis , A. intermedius Eigenmann , A. jenynsii , A. microschemos , A. rivularis Lütken , A. totae , and A. varzeae . It differs from A. brachypterygium , A. goyanensis , and A. totae by head length (24.9-28.2% SL, mean = 26.6 vs. 27.8- 33.2, mean = 29.9, 27.7-32.3, mean = 31.6, and 27.9-32.8, mean = 29.7, respectively), and by the number of humeral spots (1 vs. 2, except in A. totae , which has one). It differs from A. burgerai and A. intermedius by shape of the dentary teeth (abruptly decreasing in size after fourth tooth vs. teeth gradually decreasing in size posteriorly), and orbital diameter (24.9-31.9% HL, mean = 27.9 vs. 34.6-40.6, mean = 38.0, 32.5- 47.8, mean = 39.0, respectively); from A. jenynsii by the number of branched anal-fin rays (15-17, mean = 15.8 vs. 13-15, mean = 14) and upper jaw length (40.6-50.0% HL, mean = 44.9 vs. 35.9- 39.5, mean = 37.4); from A. rivularis by body depth (27.4- 33.1% SL, mean = 30.5 vs. 35.0-46.0, mean = 40.3), and by the number of humeral spots (1 vs. 2); from A. varzeae by the number of lateral line scales (35-36, mean = 35.4 vs. 37-42, mean = 39), caudal-peduncle length (13.6-16.9% SL, mean = 15.2 vs. 10.5-13.9, mean = 12.4) and orbital diameter (24.9-31.9% HL, mean = 27.9 vs. 30.9-44.5, mean = 37.9). Furthermore, it differs from A. microschemos and A. totae by the number of maxillary teeth (1 vs. 2-3 and 2-5, respectively). Astyanax courensis differs from only sympatric Astyanax species , A. goyanensis , by the number of pelvic-fin rays (8 vs. 7), and number of maxillary teeth (1 vs. 2-5), and by prepectoral distance (23.7-27.8% SL, mean = 26.4 vs. 27.7-32.0, mean = 30.4).

Description. Morphometric data summarized in Table 1. Body compressed and elongate; greatest body depth usually immediately anterior to dorsal-fin origin. Dorsal profile of head between vertical through posterior nostril and tip of supraoccipital spine straight or slightly convex. Profile of body convex from tip of supraocciptal spine to base of last dorsal-fin ray, and straight from that point to adipose-fin origin. Ventral profile of head convex. Ventral profile of body slightly convex from pectoral-fin insertion to anal-fin origin. Body profile along anal-fin base posterodorsally slanted. Caudal peduncle elongated, nearly straight to slightly concave along both dorsal and ventral margins.

Snout rounded from margin of upper lip to vertical through anterior nostrils. Head relatively small. Mouth terminal, lower jaw slightly projected over upper jaw. Maxilla extending posteriorly to vertical through anterior half of orbit, slightly curved, and aligned at angle of approximately 45 degrees relative to longitudinal body axis. Maxilla slightly widened anteroposteriorly.

Premaxilla with two tooth rows; outer row with four to six tri- to pentacuspid teeth with central cusp longest. Five teeth in inner premaxillary row; teeth gradually decreasing in length from first towards fourth tooth with last tooth distinctly smaller: teeth with five to seven cusps with central cusp twice as long and broad as other cusps. Maxilla with one tooth (rarely two) with three to five cusps, and central cusp longest. Three to four anteriormost dentary teeth larger, with five or seven cusps, followed by one medium-sized tooth with three to five cusps, and then five to seven teeth with one to three cusps. Central cusp in all teeth two to three times as long and broad as other cusps. All cusp tips slightly curved posteriorly towards oral cavity ( Fig. 6 ).

Dorsal-fin rays ii,9 (n = 30); first unbranched ray approximately half length of second ray. Distal margin of dorsal fin nearly straight or slightly convex. Dorsal-fin origin anterior at middle of SL. Adipose-fin origin approximately at vertical through insertion of base of last anal-fin ray. Anal-fin rays iii-v,15-17 (mean = 15.8, n = 30). First unbranched ray normally only apparent in c&s specimens. Anal-fin profile nearly straight in males, and smoothly concave in females. Anal-fin origin posterior to vertical through base of last dorsal-fin ray. Anal-fin rays of males bearing one pair of small bony hooks along posterolateral border of each segment of lepidotrichia, usually along last unbranched ray to sixth anterior branched ray. Hooks more numerous along second through fourth branched rays, and usually located along posteriormost branch and distal 1/2 to 2/3 of each ray.

Pectoral-fin rays i,10-12 (mean = 10.7, n = 30). Tip of pectoral fin not reaching the pelvic-fin origin in both sexes. Pelvic-fin rays i,7 (n = 30). Pelvic-fin origin slightly anterior to vertical through dorsal-fin origin. Tip of pelvic fin surpassing the urogenital opening in males, and only reaching that point in females. Caudal fin forked and unscaled, lobes similar in size, with 19 principal rays (one specimen with 17). Dorsal procurrent rays 10-13, and ventral procurrent rays 9-11 (n = 7).

Lateral line complete with 35-36 scales (mean = 35.4, n = 30). Scale rows between dorsal-fin origin and lateral line 5- 6 (mean = 5.4, n = 30); 3-4 scale rows between lateral line and pelvic-fin origin (mean = 3.9, n = 30). Predorsal scales 11-13 (mean = 12.2, n = 29) usually arranged in regular series. Scale rows around caudal peduncle 14 (n = 30). Axillary scale on pelvic-fin insertion posteriorly extended covering 1-2 scales. Scale sheath along anal-fin base 5-8 scales, in single series, covering base of anteriormost rays.

Precaudal vertebrae 17-18; caudal vertebrae 17-18; total vertebrae 34-35 (n = 7). Supraneurals 5-6 (n = 7). Upper branch of gill rakers 6-7, lower branch 11-12 (n = 7).

Color in alcohol. General body color yellowish-brown. Dark chromatophores scattered on lateral portion of head, but more densely concentrated on snout and anterior border of eye. Lateral portion of body with scales posteriorly bordered by dark pigment and forming reticulate pattern. Body with black, pigmented, midlateral stripe extending from the upper border of the opercle to the caudal-fin base; dark pigmentation present on middle caudal-fin rays. Midlateral body stripe expanded dorsally and ventrally proximate to caudal-fin base, forming small caudal spot. Humeral spot conspicuous, vertically elongate with superior portion of spot wider, located over second to fourth vertical series of scales and extending over 2 to 3 horizontal series of scales above lateral line; and inferior portion of spot narrower, and extending over 1 to 2 horizontal series of scales below lateral line. Region just posterior to the humeral spot pale in some specimens. Fins with few dispersed dark chromatophores ( Fig. 5 ). Specimens retained orange and yellowish pigment on all fins after several days fixation in formalin.

Color in life. Immediately after capture, specimens with overall golden body coloration and orangish to red fins. Humeral spot faint black. Midlateral stripe and caudal-peduncle spot less conspicuous than after preservation. Caudal-fin middle rays black, and median portion of lobes yellowish white.

Sexual dimorphism. Males of Astyanax courensis are easily recognized by the presence of small bony hooks on the anal-fin rays. Also, males and females differ by anal-fin shape, which is nearly straight in males and concave in females.Gill glands (Burns & Weitzman, 1996) were not found macroscopically on first gill arch in either males or females.

Distribution. Astyanax courensis is known from the rio dos Couros basin, tributary of rio Tocantinzinho, upper rio Tocantins basin, Alto Paraíso de Goiás, Chapada dos Veadeiros, Goiás State, Brazil ( Fig. 3 ).

Ecological notes. See features about rio dos Couros in the ecological notes above. Most of the specimens were collected on the stretch downstream from the waterfall ( Fig. 4a ). Also it was observed few specimens on the stretch upstream of waterfall. Only four species were collected syntopically with A. courensis : Characidium stigmosum , C. aff. zebra , Gymnotocinclus anosteos and Trichomycterus sp. Stomach contents of five specimen (UFRGS 11290) presented Plecoptera, Trichoptera, Chironomidae (Diptera) , authochthonous and allochthonous insects, and digested vegetal organic matter. The stomachs were partially full.

Etymology. The specific name courensis is in reference to the type-locality, rio dos Couros, an important tributary of rio Tocantinzinho, upper rio Tocantins basin. An adjective.

Figures

Fig. 5. Astyanax courensis, new species, UFRGS 11499, holotype, female, 54.2 mm SL; rio dos Couros at Parque Portal da Chapada, tributary of rio Tocantinzinho, upper rio Tocantins basin, Alto Paraíso de Goiás, Goiás State, Brazil.

Fig. 6. Astyanax courensis, new species, UFRGS 11290, 45.0 mm SL. Scanning electronic microscopy images of upper and lower jaws, left side, lateral view. Scale bar = 1 mm.

Fig. 3. Distribution of Astyanax goyanensis (circles) and A. courensis, new species (square), on upper rio Tocantins, Alto Paraíso de Goiás, Goiás State, Brazil. A, rio Tocantinzinho; B, rio Tocantins; C, rio Paranã; DF, Distrito Federal. Symbols can represent more than one lot or locality. Base map prepared by Marilyn Weitzman.

Fig. 4. (a) Rio dos Couros downstream from the Cachoeira São Bento, type-locality of Astyanax courensis, new species; (b) small stream tributary of rio dos Couros at Parque Portal da Chapada, locality of collection of Astyanax goyanensis.