Odontostilbe nareuda, Bührnheim & Malabarba, 2006

Bührnheim, Cristina M. & Malabarba, Luiz R., 2006, Redescription of the type species of Odontostilbe Cope, 1870 (Teleostei: Characidae: Cheirodontinae), and description of three new species from the Amazon basin, Neotropical Ichthyology 4 (2), pp. 167-196 : 184-188

Odontostilbe nareuda , new species

Fig. 19

Holotype. CBF 09621, 1 (male 33.1 mm), Bolivia, Pando, [río Orthon - rio Madeira basin], lake on right bank of río Nareuda, around 3-4 km above mouth of río Tahuamanu , H. Ortega et al., 10 Sep 1996.

Paratypes. BOLIVIA, PANDO: FMNH 106433 , 4 m of 17 (2 males 29.4-31.4 mm SL, 1 male 31.6 mm SL c&s, 1 female? 32.3 mm SL, 13 unsexed 19.5-27.1 mm SL not measured), same data as holotype . FMNH 106428 , 1 m (unsexed 30.9 mm SL), rio Madeira basin, lake on the right bank of río Nareuda, ca. 3-4 km above mouth of río Tahuamanu , H. Ortega et al., 10 Sep 1996 . FMNH 106430 , 1 m (unsexed 38.0 mm SL), rio Madeira basin, lake on the right bank of río Nareuda, ca. 5 km from mouth of río Tahuamanu , J. Sarmiento & S. Barrera, 11 Sep 1996 . BRAZIL, RONDÔNIA: MCP 38417, 20 (1 male 28.8 mm SL, 19 unsexed 24.0- 28.6 mm SL), [Calama], poço da Angélica, rio Madeira , M. Goulding, 12 Dec 1980 , formerly MZUSP 42837 . MZUSP 87759 , 1 m (female 35.3 mm SL), Calama, M. Goulding, 2 Feb 1981 . MZUSP 87760 , 5 m (4 unsexed 27.0- 34.5 mm SL, and 1 unsexed c&s 27.5 mm SL), same data as MCP 38417 .

Non-type material. Río Madeira basin, BRAZIL, AMAZONAS: MZUSP 42837 , 200 (unsexed 21.5-28.3 mm SL), [Calama], poço da Angélica, rio Madeira. Río Mamoré basin , BOLIVIA, MOTACUSAL: MNHN 1989-1465 , 10 of 112 (7 unsexed 21.5- 25.7 mm SL, 3m unsexed- 26.7-28.7 mm SL), río Isiboro, río Mamoré basin. Río Purus basin , BRAZIL, ACRE : MZUSP 87752 , 2 (unsexed 26.3-26.8 mm SL), rio Acre, between Seringal Paraíso and lago Amapá . MZUSP 87753 , 1 (unsexed 33.1 mm SL), Manoel Urbano, rio Purus. Río Orthon - lower Río Beni basin , BO- LIVIA, PANDO: FMNH 106429 , 1 (unsexed 20.0 mm SL), lake on the right bank of río Nareuda, around 3-4 km above mouth of río Tahuamanu . FMNH 106432 , 3 (unsexed 21.9-30.9 m SL), approx. 2-3 km above mouth of río Muyumanu . FMNH 106434 , 2 (unsexed 29.2- 29.2 mm SL), right bank of stream Filadelfia, approx. 10 km from mouth of río Nareuda . FMNH 106435 , 2 (unsexed 21.0- 21.5 mm SL), hidden lake on right bank of río Tahuamanu , approx. 500 m from mouth of río Nareuda . FMNH 106436 , 1 (unsexed 23.2 mm SL), río Tahuamanu at rocks and island archipelago and rapids, 68 km below mouth of río Nareuda . FMNH 106462 , 1 m (unsexed 28.3 mm SL), río Nareuda at camp, altitude 250 m.

Diagnosis. Odontostilbe nareuda basically differs from all other species by larger anal-fin base length, 30.6-32.8% SL (e.g. vs. 23.5-29.4% SL in O. fugitiva , Fig. 20 , or 23.1-28.5% SL in O. dierythrura ), and higher anal-fin counts, 24-26 (vs. 16-24

C. M. Bührnheim & L. R. Malabarba 185

for all other species). Adittionaly, gill raker counts on upper branch 5-6 and lower branch 11-12 of O. nareuda differ from sympatric species O. fugitiva with mostly 6-7 on upper and 12-13 on lower ( Figs. 13 a-b).

Description. Morphometric data given in Table 3. Largest male 33.1 mm SL; female 32.3 mm SL. Body elongate and compressed. Greatest body depth at dorsal-fin origin. Snout usually pointed; not protuded in males. Dorsal profile ascends slightly convex from snout to dorsal-fin origin, and descends straight from that point to caudal peduncle. Ventral profile convex from lower jaw to anal-fin origin, and straight along anal-fin base. Caudal peduncle slightly longer than deep.

Head relatively small. Posterior margin of opercle sinusoidal with upper portion concave and lower portion convex. Mouth terminal. Maxilla short, oblique; posterior tip reaching near or to vertical at anterior eye border, and ending at level of inferior eye border. Cleared and stained specimens (2). Premaxillary teeth 5, bearing 7-9 cusps; midcentral cusp longer than lateral cusps; smaller lateral cusps of each tooth overlap cusps of adjacent teeth, except anteriormost teeth ( Fig. 21 ). Premaxillary teeth juxtaposed externally to dentary teeth, leaving premaxillary tooth cusps exposed when mouth closed. Maxilla with 2 teeth bearing 2-8 cusps, usually decreasing cusp number to posterior tip of maxilla. Dentary teeth 8-11 bearing 1-7 cusps, gradually decreasing in size posteriorly; anterior 6 teeth large with 5-7 cusps, and remainder small with 1-4 cusps. Smaller cusps of dentary teeth overlaping adjacent tooth cusps, usually not in posteriormost teeth.All dentary tooth cusps slightly recurved towards interior of mouth.

Dorsal-fin rays ii (17) or 9 (17). Dorsal-fin origin slightly posterior to midlength of body, and slightly posterior to vertical through pelvic-fin origin.Anal-fin rays v (16), vi(1), 23(3), 24 (9), 25(4), or 26(1). Anal-fin distal border concave, about 7 anterior branched rays longer than posterior rays. Pectoralfin rays i (17), 9(1), 10(9), or 11 (7). Unbranched pectoral-fin ray reaching or not reaching pelvic-fin origin, extending beyond pelvic-fin origin in mature males. Pelvic-fin rays i (20), 6(1), or 7 (19). No evident elongation of unbranched dorsal or pelvic-fin rays in males. Lateral skin border of unbranched pectoral-fin rays and unbranched pelvic-fin rays thickened in mature males, bearing thin laterodorsal projection of hard tissue covered with soft tissue. Principal caudal-fin rays 19 (20). Procurrent caudal-fin rays: dorsal 11 (7), 12(8), or 13(2); ventral 9(7) or 10 (10). Sometimes anterior ventral procurrent caudal-fin rays modified, distally bifurcated. Caudal-fin ray flaps ventrally on 4 th- 7 th rays of upper lobe, and dorsally on 14 th- 15 th rays of lower lobe. Adipose-fin at vertical through last analfin ray insertion.

Holotype and paratype males of FMNH 106433 are unique, all having not totally developed hooks. Males with acute, retrorse hooks on posterior margin of pelvic and anal-fin rays. One or two paired or unpaired hooks per segment of lepidotrichia on last unbranched anal-fin ray, and 1 st to 9 th anal-fin branched rays, positioned at middistal length of rays. One or two unpaired hooks per segment of lepidotrichia along almost entire length of 1 st to 7 th branched pelvic-fin rays, and reaching tip of fin rays (except on 1 st branched pelvic-fin ray, on midlenght portion).

Scales cycloid; lateral line complete 35(1) or 36 (6); predorsal row 10(6) or 11 (10); scale rows between lateral line and dorsal-fin origin 5 (7) or 6(6); scale rows between lateral line and anal-fin origin 4(15), scale near pelvic-fin origin usually smaller than others); scale rows around caudal peduncle 14 (7). Triangular modified scale on pelvic-fin base extends posteriorly covering 1-3 scales. Scales on anal-fin base 6- 7.

Cleared and stained specimens (2): supraneurals 4(1) or 5(1); precaudal vertebrae, 16(2); caudal vertebrae 19(2). Gill rakers (counted in 15 alcohol specimens, and 2 c&s), upper 5(3) or 6 (13); lower 10(3), 11(7), or 12 (6) (1-2 on hypobranchial). Upper gill rakers with 1-3 recurved denticles on anterolateral border, and none or 1 similar denticle on posterolateral border; lower gill rakers with none to 3 recurved denticles on anterolateral border (1-4 anteriormost lower gill rakers with none or 1 denticle on posterolateral border); posteriormost lower gill raker with 3 denticles on anterolateral border, and 1- 2 similar denticles on posterolateral border ( Fig. 22 ). All denticulation mainly on basal portion of gill rakers.

Color in alcohol. General ground body color brownish or pale yellow. Dorsal portion of body dark from head to caudal peduncle; dark chromatophores mostly on scale borders, forming reticulated pattern. Pigmented scales not extending laterally on body, no distinct dark chromatophores on pseudotympanum area. Dorsal fin entirely with dark chromatophores scattered along all fin rays, more densely along 1 st and 2 nd unbranched dorsal-fin rays. Pectoral and pelvic fins with scattered dark chromatophores, more numerous on anteriormost portions of fins. Holotype with pelvic fins hyaline. Anal fin mostly pigmented, dark chromatophores spread on all fin rays, except at tips of last unbranched fin ray and 1 st branched fin ray. Adipose fin hyaline. Caudal fin almost entirely covered with diffuse dark chromatophores along fin rays, clear areas on base of caudal-fin lobes just behind caudal-fin spot. Rounded black to brown spot on base of caudal fin, reaching upper and lower border of peduncle, usually lighter near ventral border, sometimes extending little on proximal portion of 7 th to 12 th central caudal-fin rays.

Numerous chromatophores on snout, as well as upper and lower lips (on lower lip these almost form line). Numerous dark chromatophores on anteriormost portion of maxilla, and 1 st infraorbital. Pigmentation on top of head on frontals and parietals, and deep-lying dark chromatophores cover brain membranes below frontals, parietals, and fontanel. Body with faint dark midlateral stripe, sometimes reduced to line along longitudinal body axis, beginning below dorsal fin, above lateral line, and extending to caudal spot. Belly pale, almost without chromatophores below lateral line, except above analfin base with 7 to 12 chevron shaped markings. Guanine on eye iris, interopercle, opercle, subopercle, isthmus, 2 nd to 4 th infraorbitals, lateral portion of parietals just behind eye, and belly. Guanine more evident in MCP 38417, and MZUSP 87760 specimens. Holotype with some guanine.

Odontostilbe nareuda seems to have fewer dark chromatophores than similar species such as O. fugitiva , O. dierythrura , and O. parecis , and another new species from río Madre de Dios (in manuscript), all of these occur in the rio Madeira basin. Except for O. parecis from rio Guaporé basin, the other three species were found to be sympatric with O. nareuda .

Sexual dimorphism. Only three males available, holotype and two paratypes, but these are not fully mature, without completely developed hooks. These males have longer pectoralfin rays in contrast with specimens with undetermined sex, statistically significant in test for coincidental regressions (F (2, 276) = 28.5, p<0.00) ( Fig. 23 ). The snout profile of holotype is slightly protruded in comparison with the unsexed paratype FMNH 106433 ( Fig. 19 ). Gill gland not found in males of O. nareuda . Absence of this gill gland probably explained by lack of mature males among examined specimens .

Distribution. Odontostilbe nareuda is known from the lower río Beni basin, in the ríos Nareuda and Muyumanu, of the ríos Tahuamanu-Orthon drainage that runs parallel to the río Madre de Dios, and the middle rio Madeira ( Fig. 18 ). However, it may be widespread in the rio Madeira basin. Some specimens from the upper rio Mamoré basin were tentatively identified as O. nareuda . Also, three specimens from the rio Purus match the larger anal-fin base diagnostic of O. nareuda . A somewhat similar distribution was observed for Creagrutus occidaneus that occurs in río Madre de Dios and upper rio Purus (Vari & Harold, 2001). Further samples of these regions including mature males and females are needed to assure these distributions.

Etymology. In allusion to the type-locality, in the río Nareuda.

Ecological notes. FMNH field notes for O. nareuda indicate that it occurs in oxbow lakes, river or small river habitats in forest, having whitewater or turbid-white water. The bottom was sandy or muddy substrate with sticks, logs, and leaves. Nevertheless the río Nareuda is mostly a blackwater river as noted by Machado-Alllison et al. (1999a), all the locality notes of FMNH lots refer to whitewater, except FMNH 106430 which mentions clearwater of brown color. The lower río Nareuda seems to be influenced by whitewaters of the río Tahuamanu - río Orthon basin. The FMNH specimens all came from the AquaRAP expedition in the upper río Orthon basin, Bolívia. These specimens were originally identified as Cheirodon fugitiva , Odontostilbe fugitiva or Odontostilbe sp. ( Chernoff et al., 1999; Sarmiento et al., 1999). Specimens identified for the AquaRAP expedition as O. paraguayensis , and listed as that species by Willink et al. (1999) as “believed to be” a new record for the Bolivian Amazon, actually are O. nareuda or an undescribed species of cheirodontine. Both species were collected together, being probably syntopic. Machado- Allison et al. (1999b) detailed the abundance of species regarding the field station that corresponds to FMNH lots of the holotype and some paratypes (FMNH 106433) and cited “ O. paraguayensis ” as the most abundant species, and “ Cheirodon fugitiva ” the fifth ranked, being “typically from cochas or flooded lakes”.

Figures

Fig 21. Dentition of Odontostilbe nareuda, FMNH 106433, male 31.6 mmSL.SEM photograph ofleft side premaxilla (top), maxilla (middle), and dentary (bottom).

Fig. 19. Holotype of Odontostilbe nareuda, CBF 09621, male 33.1 mm (top), and paratype FMNH 106433, possibly a female 32.3 mm SL, not showing dimorphic characters of males (bottom).

Fig. 20. Anal-fin base as a function of standard length for males, females and unsexed specimens of Odontostilbe fugitiva against Odontostilbe nareuda.

Fig. 13. Upper and lower gill rakers counts of Odontostilbe fugitiva populations, and three new species Odontostilbe ecuadorensis, Odontostilbe nareuda, and Odontostilbe parecis.

Fig. 22. First gill arch of Odontostilbenareuda,FMNH 106433, unsexed 29.2 mm SL. SEM photographs of the left side gill arch (top), in detail gill rakers on upper branchial branch (middle), and gill rakers on lower branchial branch (bottom). Lateral view.

Fig. 23. Pectoral-fin length as a function of standard length for males versus unsexed specimens of Odontostilbe nareuda.

Figs. 18. Distribution of Odontostilbe ecuadorensis (triangles), Odontostilbe nareuda (squares), and Odontostilbe parecis (losangles). Symbols can represent more than one lot, and more than one locality.