Characidium helmeri, Zanata, Angela M., Sarmento-Soares, Luisa M. & Martins-Pinheiro, Ronaldo F., 2015

Zanata, Angela M., Sarmento-Soares, Luisa M. & Martins-Pinheiro, Ronaldo F., 2015, A new species of Characidium Reinhardt (Ostariophysi: Characiformes: Crenuchidae) from coastal rivers in the extreme south of Bahia, Brazil, Zootaxa 4040 (3), pp. 371-383 : 372-378

Characidium helmeri , new species

( Fig. 1–4 )

Characidium sp. 2— Sarmento-Soares et al., 2009: 146 (species list).

Holotype. MNRJ 42610, 40.4 mm SL, Brazil, Bahia, Prado, rio Ribeirão, on road between Cumuruxatiba and Corumbau, tributary of rio Cahy, 17º00’45”S 39º12’07”W, 17 m above sea level, L.M. Sarmento-Soares, R.F. Martins-Pinheiro, A.T. Aranda & C.C. Chamon, 24 Oct 2004.

Paratype s. All from Brazil, Bahia. Prado: MNRJ 29038, 14, 21.5–35.5 mm SL, MBML 3834, 5, 19.5–26.8 mm SL, MBML 7365, 1 CS, 26.9 mm SL, collected with holotype. MZUSP 27003, 1, 32.2 mm SL, Cumuruxatiba, rio do Peixe Grande, 17°05’25” S 39°12’54”W, 17 m above sea level, R.M.C. Castro, 20 Feb 1979. MZUSP 74029, 4, 23.4–28.5 mm SL, rio Imbassuaba at Fazenda Embaçoaba, 17°04’53” S, 39°15’56”W, 33 m above sea level, Expedição MZUSP / USNM, 20 Mar 1985. MZUSP 112666, 24, 1 mol, 16.7–30.3 mm SL, rio Ribeirão, tributary of rio Cahy Braço Norte, on road between Barra do Cahy and Ponta do Corumbau, 17º00'45"S, 39º12'05"W, 27m above sea level, O.T. Oyakawa, A.M. Zanata, P. Camelier & T.F. Teixeira, 9 Aug 2012. MZUSP 112653, 21, 1 mol, rio Cahy Braço Norte, on road between Barra do Cahy and Ponta do Corumbau, 16º59’10”S, 39º12’53”W, 8 m above sea level, O.T. Oyakawa, A.M. Zanata, P. Camelier & T.F. Teixeira, 9 Aug 2012. Canavieiras: MZUSP 93899, 1, 32.4 mm SL, affluent of rio Salsa, tributary of rio Pardo on road between Ouricana and Pimenteira, 15°43’53”S, 39°07’44”W, 19 m above sea level, N.A. Menezes, O.T. Oyakawa, L.M. Sousa & J.C. Nolasco, 0 3 Apr 2006. MZUSP 112433, 1, 32.2 mm SL, affuent of rio Salsa, tributary of rio Pardo, on road between Ouricana and Pimenteira, 15°43’55”S, 39°07’45”W, 24 m above sea level, O.T. Oyakawa, A.M. Zanata, P. Camelier & T.F. Teixeira, 11 Aug 2012. Porto Seguro: MBML 531, 18, 1 CS, 17.2–36.3 mm SL, and MBML 7363, 1 CS, 28.4 mm SL, rio Trancoso, 16º35’15”S, 39º05’41”W, 9 m above sea level, R.L. Teixeira & G.I. Almeida, 0 7 Apr 2001. MBML 6633, 1, 29.1 mm SL, tributary of rio da Barra near boundaries of RPPN II Fazenda Sol Poente Trancoso, 16°31’49”S, 39°08’56”W, 30 m above sea level, J.L. Helmer, 14 Nov 2012. MBML 6645, 2, 21.9–35.4 mm SL, tributary of Córrego Manoelzinho, affluent of rio do Norte, rio da Barra microbasin in RPPN II Fazenda Sol Poente in Trancoso village, 16°31’20”S, 39°08’12”W, 31 m above sea level, J.L. Helmer, 17 Nov 2012. MBML 6652, 8, 29.6–33.4 mm SL, rio do Norte, tributary of rio da Barra, near boundary of RPPN V Fazenda Nova Esperança I in Trancoso, 16°32’39”S, 39°06’50”W, 9 m above sea level, J.L. Helmer, 20 Jul 2012. MBML 6668, 4, 35.4–39.8 mm SL, Córrego Manoelzinho, tributary of rio do Norte, affluent of rio da Barra RPPN II Fazenda Sol Poente in Trancoso village, 16°31’21”S, 39°08’29”W, 56 m above sea level, J.L. Helmer, 16 Nov 2012. MBML 6673, 1, 27.3 mm SL, rio do Norte, tributary of rio da Barra, near boundary of RPPN V Fazenda Nova Esperança I in Trancoso, 16°32’39”S, 39°06’50”W, 9 m above sea level, J.L. Helmer, 16 Nov 2012. MBML 6680, 10, 18.2–28.6 mm SL, Rio do Norte, tributary of rio da Barra in RPPN rio do Brasil in Trancoso, 16°30’40”S, 39°08’33”W, 35 m above sea level, J.L. Helmer, 23 Jul 2012. MBML 6688, 9, 26.5–27.2 mm SL, Rio da Barra near boundary of RPPN II Fazenda Sol Poente in Trancoso village, 16°32’18”S, 39°08’34’W, 20 m above sea level, J.L. Helmer, 19 Jul 2012. MBML 6700, 10, 24.3–32.1 mm SL, and MBML 7368, 1 CS, 26.8 mm SL, Rio do Norte, tributary of rio da Barra in RPPN III Fazenda Sol Nascente, in Trancoso village, 16°31’44”S, 39°07’18”W, 24 m above sea level, J.L.Helmer, 20 Jul 2012. MBML 6708, 5, 24.5–37.3 mm SL, Rio da Barra, near boundary of RPPN II Fazenda Sol Poente and Parque Nacional do Pau Brasil near Trancoso, 16°31’45”S, 39°09’02’W, 32 m above sea level, J.L.Helmer, 20 Jul 2012. MBML 6710, 13, 22,2– 31.5 mm SL, Rio da Barra after RPPN V Fazenda Nova Esperança I, in Trancoso village, 16°32’44”S, 39°06’59”W, 9 m above sea level, J.L. Helmer, 20 Jul 2012. MBML 6720, 6, 19.9–30.5 mm SL, córrego Manuelzinho, tributary of rio do Norte, tributary of rio da Barra in the RPPN II F Sol Poente in Trancoso, 16°31’21”S 39°08’29”W, 55 m above sea level, J.L. Helmer, 21 Jul 2012. MBML 6725, 2, 23.8–40.7 mm SL, Córrego Manoelzinho, tributary of rio do Norte, tributary of rio da Barra, RPPN II Fazenda Sol Poente in Trancoso, 16°31’21”S, 39°08’29’W, 55 m above sea level, J.L. Helmer, 24 Jul 2012. MBML 6755, 2, 29.9–36.6 mm SL, Rio da Barra near boundary of RPPN II Fazenda Sol Poente in Trancoso, 16°32’18”S, 39°08’34”W, 20 m above sea level, J.L. Helmer, 14 Nov 2012. MBML 6757, 2, 26.6–31.6 mm SL, Rio do Norte, tributary of rio da Barra in RPPN rio do Brasil in Trancoso, 16°30’40”S, 39°08’33”W, 35 m above sea level, J.L. Helmer, 16 Nov 2012. MBML 3963, 4, 29.7–35.6 mm SL, rio das Águas, tributary of rio Trancoso, 16º33’13”S, 39º10’03”W, 42 m above sea level, J.L. Helmer, 9 Dec 2010; MBML 3969, 1, 21.5 mm SL, same data, 8 Jun 2010.

Diagnosis. Characidium helmeri can be distinguished from congeners by having dark, vertically elongated, irregular, narrow spots or dashes, usually more evident over the midlateral stripe and/or ventral half of body, formed by high concentration of melanophores on the posterior half of scales, occurring in a somewhat curved or zigzag-shape. Also differs from congeners by having extremely reduced or complete absence of supraorbital. The new species further differs by having lateral line reduced (vs. complete, except in C. bahiense Almeida , C. interruptum Pellegrin , C. laterale (Boulenger) , C. mirim Netto-Ferreira, Birindelli & Buckup , C. nupelia Graça, Pavanelli & Buckup , C. rachovii Regan , C. stigmosum Melo & Buckup , and C. xavante Graça, Pavanelli & Buckup ); adipose fin absent (vs. present, except in C. mirim , C. nupelia , C. stigmosum , and C. xavante ); and isthmus naked on its anteriormost portion (vs. isthmus completely covered by scales in most congeners, except in C. alipioi Travassos , C. boavistae Steindachner , C. crandellii Steindachner , C. declivirostre Steindachner , C. fasciatum Reinhardt , C. gomesi Travassos , C. grajahuensis Travassos , C. japuhybense Travassos , C. lauroi Travassos , C. macrolepidotum (Peters) , C. oiticicai Travassos , C. schubarti Travassos , C. timbuiense Travassos , and C. vidali Travassos ). Characidium helmeri differs from C. bahiense , C. interruptum , C. laterale , C. mirim , C. nupelia , C. rachovii and C. xavante by having higher number of pored lateral line scales (13–22 vs. 5–11) and two series of dentary teeth (vs. one). The new species further differs from C. nupelia and C. xavante by the absence of a dark humeral blotch (vs. present) smaller number of dark vertical bars on the body, 7–12 when present (vs. 12–18). Characidium helmeri can be differentiated from C. vestigipinne , a species with adipose fin absent or reduced, by having two dentary rows of teeth, the outer with tricuspid teeth (vs. one row of conical teeth); 4 scales above lateral line and 4 below (vs. 5 above; and 5 or 6 below); and absence of roundish black marks on pelvic, dorsal, and anal fins (vs. presence). It can be further distinguished from C. stigmosum by presence of a black basicaudal dot (vs. absence), and by having pelvic, pectoral, anal, and caudal fins not dark pigmented in males (vs. pigmented).

Description. Morphometric data of holotype and selected paratypes presented in Table 1 . Body elongate and moderately compressed. Greatest body depth at vertical through dorsal-fin origin. Dorsal profile convex from upper lip to end of occipital process, slightly convex or straight from this point to origin of dorsal-fin base, convex along dorsal-fin base, almost straight between end of dorsal-fin base to origin of anteriormost dorsal procurrent caudal-fin ray. Ventral profile of head straight, except for slightly convex portion close to dentary symphysis, slightly convex from isthmus to pelvic-fin origin, straight from latter point to anal-fin origin, straight from this point to origin of anteriormost ventral procurrent caudal-fin ray. Snout triangular in lateral view, rounded dorsally. Mouth subterminal, aligned or slightly lower than ventral edge of the orbit. Distal tip of maxilla barely reaching vertical through anterior margin of orbit. Orbit approximately round, larger than snout length. Cheek thin, its depth approximately one third to one sixth of orbit diameter. Nares separated; anterior naris with raised margins, mainly on its posterior border; posterior naris considerably closer to orbit than to anterior naris and with skin flap on its anterior border. Supraorbital absent or extremely reduced and present solely in one side of head ( Fig. 3 ). Nasal bones restricted to the ossified canal, without lateral lamella. Parietal fontanel limited anteriorly by frontals. Parietal branch of supraorbital canal absent.

Dentary teeth in two rows; outer series with 6(6), 7(23), 8*(16) or 9(4) teeth, anterior tricuspid, 3 or 4 posterior unicuspid; teeth decreasing in size from symphysis; inner series with 9(2) or 12(1) several minute conical teeth inserted on edge of replacement tooth trench. Premaxilla with single series of 5(3), 6*(29), or 7 (14) conical teeth, decreasing in size from symphysis. Maxillary edentulous. Ectopterygoid with a single series of 8(1) or 9(1) conical teeth. Mesopterygoid teeth absent.

Scales cycloid; circulii absent and around 10 radii present on exposed portion of scales. Lateral line reduced; perforated scales 13*(7), 14(8), 15(6), 16(3), 17(7), 18(7), 19(2), 20(1), 22(1); total scales along longitudinal line 30(2), 31(12), 32*(22) or 33(5); horizontal scale rows above lateral line 4*(43); horizontal scale rows below lateral line 4*(43). Scales along middorsal line between supraoccipital and origin of dorsal fin around nine or ten, but usually irregularly arranged. Scale rows around caudal peduncle 13 (1) or 14*(40). Isthmus with anteriormost small portion without scales. Pseudotympanum represented by muscular hiatus at vertical through anterior portion of swimbladder and situated over rib of fifth vertebra ( Fig. 4 ).

Dorsal-fin rays ii,9(3), ii,10(12), iii,9*(25) or iii,10(2); distal margin of dorsal fin rounded. Adipose fin absent. Pectoral-fin rays 8–12 total rays, number of unbranched rays highly variable; unbranched anterior rays ii(2), iii(7), iii*(8), iv(28), ix(1) and posteriormost rays varying from by 1–4 unbranched; one specimen with all rays unbranched; number of branched rays ontogenetically variable, increasing in number with size; first and second branched pectoral-fin rays usually longest; posterior tip of pectoral fin extending beyond pelvic-fin insertion. Pelvic-fin rays highly variable, i,4,iii(1), i,4,iv (1), i,5,i (1), i,5,ii(6), i,5,iii(6), i,6,i(10), i,6,ii(7), ii,6,ii(1), i,7(1), i,7,i*(7), or i,8,i(1); second to fourth branched pelvic-fin rays longest; posterior tip of pelvic fin extending beyond anal-fin origin and usually reaching base of second branched anal-fin ray. Anal-fin rays ii,5(1) or ii,6*(42); iii,6(1); posterior margin of anal fin pointed posteriorly, with second branched usually longest; fin elements (i.e., adnate rays) on last pterygiophore 2*(43). Caudal-fin rays i,8,8,i(1), i,9,8,i(2). Dorsal procurrent caudal-fin rays 7(3); ventral procurrent caudal-fin rays 6(2) or 7(1).

Total number of vertebrae 33(1), 34(1) or 35(1); precaudal vertebrae 18(1) or 19(2); caudal vertebrae 15(2) or 16(1). Supraneural bones 4(1), 5(1) or 6(1). Epural bones 3(3). Uroneural bone 1(3). Branchiostegal rays 5(3); 4 connected to anterior ceratohyal, 1 connected to the posterior ceratohyal.

Color in alcohol. Ground color of head and body pale yellow ( Fig. 1 ). Dark stripe extending from snout to posterior margin of opercle. Dorsum of head with a large brown blotch posteriorly, occupying area from vertical through posterior margin of orbit to posterior margin of the supraoccipital bone. Ventral half of head clear, with sparse small melanophores. Dark midlateral stripe usually extending from rear of opercle to end of caudal peduncle; in some specimens stripe faded or absent. Dark humeral blotch absent. Basicaudal black spot well defined. Presence, form, and arrangement of blotches or bars on laterals of body variable. Most specimens with dorsal half of body with 7 to 10 usually inconspicuous dark primary vertical bars, broader dorsally (2 or 3 scales wide); dark and conspicuous narrow dark bars or traces vertically elongate, associated or not to the primary bars, usually more defined over longitudinal band and extending irregularly ventrally; bars on ventral half of body, when present, usually formed by high concentration of dark pigment on posterior half of scales, resulting in curved or somewhat zigzag-shaped spots or dashes, usually not reaching the midventral line of body; posterior half of body usually with vertical bars similarly shaped on dorsal and ventral half, continuous throughout midventral line. In some middle-sized or larger specimens (28.0–36.0 mm SL), spots on dorsolateral area isolated from those distributed over midlateral band and from those more ventrally positioned (when present), resulting in two or three series of spots somewhat horizontally arranged on lateral of body. Smaller specimens, up to 25.0 mm SL, usually with 10–12 continuous narrow vertical bars crossing the sides of the body; bars reaching its contralaterals ventrally on portion posterior to the pelvic fins. Dorsal, anal and caudal fins with melanophores distributed over rays; interradial membranes mostly transparent, except for a black bar near base of dorsal and anal fins. Pectoral and pelvic fins usually without pigmentation but some specimens with melanophores on fin rays.

Color in life. Ground color of dorsal half of yellowish and ventral half whitish ( Fig. 2 ). Pattern of dark spots and bars similar to specimens in alcohol; dark longitudinal stripe and spots on ventral half of body usually more evident than pigmentation on dorsal half. Fins yellowish.

Etymology. The specific name, helmeri , is a genitive noun in honor of Dr. José Luis Helmer, who collected part of the material of the species, and in recognition of his pioneer studies on the natural history of the freshwater fishes in Espírito Santo and Southern Bahia, since 1976.

Sexual dimorphism. No hooks on fins or other sexually dimorphic features were observed externally on specimens examined.

Distribution. Characidium helmeri is known from various small coastal rivers in Southern Bahia ( Fig. 5 ), in the vicinity of Canavieiras, Porto Seguro, and Prado.

Habitat and ecological notes. Characidium helmeri is apparently restricted to slow flowing river stretches, situated 8–91m above sea level, a few centimeters to 1.5 m deep, with transparent or dark water running in substrate composed by pebbles, gravel, or organic debris ( Fig. 6 ). The riparian vegetation is composed by secondary forest, with plenty floating meadows and submersed vegetation in portions of the river bank. The new species was collected syntopically with Aspidoras virgulatus Nijssen & Isbrucker, Astyana x s p., Geophagus brasiliensis (Quoy & Gaimard), Hoplerythrinus uniaeniatus (Agassiz) , Hoplias malabaricus (Bloch) , Mimagoniates microlepis Steindachner , M. sylvicola Menezes & Weitzman , Scleromystax prionotos (Nijssen & Isbrucker) , Otothyris travassosi Britski & Schaefer , Phalloceros ocellatu s Lucinda, including the endangered species Acentronichthys lepto s Eigenmann & Eigenmann and Rachoviscus graciliceps Weitzman & Cruz. The stomach contents of four specimens of C. helmeri analyzed (26.8–35.9 mm SL) contained small aquatic insect larvae, mainly Chironomidae , nymphs, fragments of insects, vegetable debris and organic matter partially digested.

Figures

FIGURE 1. Characidium helmeri, (a) holotype, MNRJ 42610, 40.4 mm SL, rio Ribeirão, tributary of rio Cahy, Bahia, Brazil; (b) paratype, MBML 531, 36.2 mm SL, rio Trancoso, Bahia, Brazil; (c) paratype, MZUSP 112653, 30.6 mm SL, rio Cahy Braço Norte, Bahia, Brazil; (d) paratype, MNRJ 29038, 23.2 mm SL, same data as holotype.

FIGURE 2. Paratype of Characidium helmeri, MZUSP 112666, 30.3 mm SL, stream on road between Barra do Cahy and Ponta do Corumbau, Bahia, Brazil; photographed live.

FIGURE 3. Head dorsum of Characidium helmeri, MBML 531, 30.1 mm SL, rio Trancoso, Bahia, Brazil. Arrow indicates vestigial supraorbital.

FIGURE 4. Pseudotympanum of Characidium helmeri, MZUSP 112666, 24.9 mm SL, rio Ribeirão, tributary of rio Cahy Braço Norte, Bahia, Brazil.

FIGURE 5. Map of small coastal river drainages between Cumuruxatiba and Canavieiras, southern Bahia, northeastern Brazil, showing distribution of the new species (blue star represents type locality).

FIGURE 6. Type locality of Characidium helmeri, new species: rio Ribeirão, rio Cahy basin, Bahia, Brazil.

Tables

TABLE 1. Morphometric data of holotype and paratypes of Characidium helmeri (number of specimens measured = 44). The range includes the holotype. SD = standard deviation.

	Holotype	Range	Mean	SD
Total length (mm)	51.6	26.7–51.6	–	–
Standard length (mm)	40.4	20.1–40.4	–	–
Percents of standard length
Depth at dorsal-fin origin	30.9	23.8–30.9	26.6	1.5
Depth at anal-fin origin	22.3	16.3–22.3	18.9	1.2
Caudal-peduncle depth	13.9	11.0–14.5	12.8	0.8
Caudal-peduncle length	18.8	15.9–21.6	19.0	1.3
Snout to dorsal-fin origin	49.3	46.7–52.2	49.0	1.4
Snout to pectoral-fin origin	23.3	22.6–29.4	26.3	1.6
Snout to pelvic-fin origin	54.0	51.2–56.7	53.9	1.3
Snout to anal-fin origin	77.2	72.7–79.9	76.7	1.5
Anal-apex distance	98.5	94.2–100.7	98.0	1.8
Body width	16.8	12.4–16.8	14.2	1.1
Head length	23.5	22.3–28.9	25.9	1.4
Percents of head length
Horizontal eye diameter	26.3	26.3–34.4	31.3	1.4
Snout length	20.0	19.0–25.4	21.3	1.6
Snout to maxillary tip	26.3	22.8–29.2	25.9	1.5
Anterior naris to orbit	9.5	6.3–11.6	9.3	1.2
Posterior naris to orbit	4.2	2.8–5.1	3.9	0.7
Cheek depth	9.5	6.2–11.3	8.3	1.2
Least interorbital width	17.9	13.1–17.9	15.3	1.3