Deuterodon pedri Eigenmann, 1908

Silva, Priscilla C., Malabarba, Maria C. & Malabarba, Luiz R., 2017, Using ancient DNA to unravel taxonomic puzzles: the identity of Deuterodon pedri (Ostariophysi: Characidae), Neotropical Ichthyology (e 160141) 15 (1), pp. 1-12 : 6-8

Deuterodon pedri Eigenmann, 1908

Figs. 1 , 3 a-b, 5-7, Tab. 2

Deuterodon pedri Eigenmann, 1908:98 (brief description). -Eigenmann, 1927:348 (description; type locality: Santa Anna de Ferros, Minas Gerais, Brazil). -Lucena, Lucena, 2002: 119 (placed as incertae sedis in Characidae ). - Lucena, Lucena, 2013: 598 (MCZ 21081 designated as lectotype). -Coutinho-Sanches, Dergam, 2015: 9 (Cytogenetic data).

Diagnosis. Deuterodon pedri can be distinguished from all congeners by the following combination of characters: a characteristic pigmentation on the two or three longitudinal and dorsolateral series of scales below the dorsal fin, each scale showing an arched and well-delineated strip at the distal margin of the free border; this strip is either dark brown when chromatophores are expanded ( Fig. 5a ) or translucent when chromatophores are contracted ( Fig. 5b ) – in either case it is clearly distinguishable from the pigmentation of the whole scale; dentary teeth decreasing gradually in size; number of anal-fin rays 18-21 in females (n=26) and 22-24 in males (n=3); longitudinal lateral silver band starting 5 or 6 scales posterior to upper margin of the opercle; humeral spot bar-shaped, vertically elongated above and below the lateral line; bony hooks only on anal-fin rays of mature males.

Deuterodon pedri can be further differentiated from morphologically similar species of the genus Astyanax that occur in Atlantic coastal river basins by the higher number of perforated scales in the lateral line (39-41 vs. 35-38 in most of species), except A. aff. fasciatus (Cuvier, 1819) , A. parahybae Eigenmann, 1908 and A. taeniatus (Jenyns, 1842) . From A. aff. fasciatus , A. parahybae and A. scabripinnis (Jenyns, 1842) it can be distinguished by the dentary teeth decreasing gradually in size posteriorly (vs. dentary teeth decreasing abruptly after the fourth tooth). From A. taeniatus , D. pedri can be distinguished by the absence of a gap between the symphyseal teeth of dentary and by a rectangular and vertically elongate humeral spot (vs. the presence of a gap between the symphyseal dentary teeth and humeral spot shaped like a comma).

Description. Morphometric data are summarized in Tab. 2. Body compressed and elongated; deepest at dorsal-fin origin. Snout profile slightly rounded from margin of upper lip to vertical through anterior nostrils. Dorsal profile of head straight between vertical through posterior nostril and tip of supraoccipital spine. Body profile convex from tip of supraoccipital spine to dorsal-fin base; ventrally slanted from this point to caudal peduncle. Ventral profile of body convex from margin of lower lip to pelvic-fin origin, and straight from that point to anal-fin origin. Body profile along anal-fin base dorsally slanted. Caudal peduncle elongated and nearly straight to slightly concave along both dorsal and ventral margins.

Head small. Mouth terminal or slightly sub-terminal. Maxilla extending posteriorly to vertical through anterior margin of orbit, slightly oblique. Anterodorsal border of maxilla slightly concave, posterodorsal border slightly convex, and ventral border convex.

Premaxilla with two tooth rows; outer row with three (6) or four (5) teeth bearing four, five or six cusps with central cusp longer. Five teeth (11) on inner row, gradually decreasing in size from first to fifth teeth. Symphyseal premaxillary teeth of inner series distinctively narrower than other teeth and asymmetrical, with two or three short cusps shorter on medial side near symphysis, followed by a high cusp and another three or four short cusps on lateral side of tooth. Teeth with five to nine cusps, with central cusp longer and as broad as other cusps. Maxilla with three (10) or four (1) teeth with five to seven cusps (usually 5 or 6), central cusp longest. Seven or six anteriormost dentary teeth larger than other teeth, with five to eight cusps, followed by three or four teeth gradually decreasing with three to five cusps. Central cusp in all teeth as long and broad as other cusps. Symphyseal teeth of dentary narrower than others with seven or eight cusps.

Dorsal-fin rays ii,9(27). Distal margin of dorsal fin straight or slightly convex. Dorsal-fin origin approximately at middle of SL. Anal-fin rays ii-iv, 18(5), 19(15), 20(4), 21(2) in females and 22(1), 23(1), 24(1) in males. Anal-fin distal border concave, with rays decreasing in size, with anterior-most rays much longer than others. Anal-fin origin located approximately on vertical through base of posterior third portion of dorsal-fin. Pectoral-fin rays i, 11(4), 12(15), 13(9). Pectoral-fin tip falls one or two scales short of vertical through pelvic-fin insertion or reaching pelvic-fin origin in some specimens. Pelvic-fin rays i(9), ii(18), 7(27). Dorsal-fin origin located at vertical line through first third part of pelvic-fin. Tip of adpressed pelvic fin falls one or two scales short of anal-fin origin. Caudal-fin forked with 18(1), 19(22), 20(2) principal rays. Dorsal procurrent rays 11(1) or 12(1). Ventral procurrent rays 10(2).

Lateral line slightly curved anteriorly, completely pored, with 38(2), 39(10), 40(13) or 41(4) (mean= 39.7, n = 29) perforated scales. Horizontal scale rows between dorsal-fin origin and lateral line 5(26) or 6(1). Horizontal scale rows between lateral line and pelvic-fin origin 4(27). Pre-dorsal scales 9(1), 10(5), 11(15), 12(6), arranged in regular or irregular series. Thirteen (12) or fourteen (13) scale rows around caudal peduncle. Scale sheath along anal-fin base formed by six to ten scales in a single series and covering base of anteriormost rays.

Precaudal vertebrae 16(2); caudal vertebrae 21(2); total vertebrae 37(2). Supraneurals 5(2). First gill-raker upper limb of 6(9), 7(4), or 8(2) + lower branch 11(8), 12(6) or 13(1). Anal pterygiophores 20(2). Dorsal pterygiophores 10(2).

Coloration in alcohol. Dorsal and dorsolateral portions of head light brown. Infraorbitals, preopercle and opercular bones silver, without chromatophores or rarely a few. Lips yellow to light brown, snout with concentration of few chromatophores. Dorsal and dorsolateral portion of body dark brown. Scales above lateral band showing an arched and well-delineated strip bordering the posterior margin. This strip is either dark brown when chromatophores are expanded ( Fig. 5a ) or translucent when chromatophores are contracted ( Fig. 5b ); in any case it is clearly distinguishable from the pigmentation of the whole scale. A conspicuous dark or silver midlateral band extending from two scales after humeral spot to the middle caudal-fin rays crossing a slightly rectangular caudal spot. Humeral spot vertical and bar-shaped, extended for two or three scales above and one or two scales below lateral line. Pectoral-, pelvic-, and anal-fins hyaline. Dorsal fin usually hyaline; in some cases with disperse chromatophores on distal portion of rays. Caudal-fin border slightly black ( Fig. 6 ).

Sexual dimorphism. One pair of bony hooks per segment are present on each lepidotrichium along the anal-fin rays of mature males. They are delicate and narrow, distributed from the 4th unbranched ray to the 12 th to 19 th branched rays. The number of segments bearing bony hooks decreases gradually from the anterior to the posterior rays on all observed males. Males have a higher number of rays (22-24) than females (18-21). Gill glands were not observed on first gill arch in either males or females.

Geographical distribution. Until recently, Deuterodon pedri was considered endemic to the rio Santo Antônio basin (its type locality). The latest collecting trips have found the species in the rio Guanhães, which is a tributary of the rio Santo Antônio, and at the confluence of the rio Brumadinho and the rio Caraça, which are tributaries of the rio Piracicaba. All of these are sub-drainages of the rio Doce ( Fig. 7 ).

e160141[7] Ecological notes. Deuterodon pedri is found in localities with rapid-to-median speed dark waters with substrates of rocks and sand. At the type locality, this species is syntopic with other endemic species from the rio Santo Antônio basin (e.g., Henochilus wheatlandii Garman ).

Conservation status. According to IUCN criteria, we recommend that D. pedri be classified as an Endangered species (EN). The species is known from an Extent of Occurrence (EOO) of approximately 4,900 km 2 (B1). There is a significant continued decline in habitat quality [criterion B1b(iii)] from continuous extensive iron ore quarrying and e160141[8] from the rupture of two dams in 2015 that released a large amount of iron ore waste, which contaminated most of the rio Doce, including the area between the rio Santo Antônio and rio Piracicaba, where the species is found. This accident has been reported to have eliminated all endemic flora and fauna in the affected waterways (Lambertz, Dergam, 2015). Additionally, the habitat of the species has been severely fragmented by hydroelectric power dams that modify river hydrodynamics, by quarrying activities that renders river stretches uninhabitable and due to the presence of 35 exotic fish species in that drainage (Barros et al., 2012).

Figures

Fig. 1. Deuterodon pedri, MCZ 21081, lectotype, 78.56 mm SL and original labels.

Fig. 3 Two paralectotypes of Deuterodon pedri, MCZ 17510. a-c. Photograph and X-ray computed tomography of the paralectotype with 72.1 mm SL, showing the dentary teeth decreasing gradually in size, corresponding to D. pedri. b-d. Photograph and X-ray computed tomography of the paralectotype with 58.6 mm SL, showing the dentary teeth decreasing abruptly, corresponding to Astyanax intermedius.

Fig. 5. Detailed images of the dorsolateral series of scales in Deuterodon pedri, showing their pigmentation pattern, each scale showing an arched and well delineated strip at the distal margin of the free border that is either dark brown when chromatophores are expanded (a. MNRJ 38463, 51.18 mm SL) or translucent when chromatophores are contracted (b. MCN 19698, 85.70 mm SL).

Fig. 6. Recently collected specimens of Deuterodon pedri showing variability according to sex and body size: a, female, MCN 19697, 79.82 mm SL; b, female, MCN 19698, 85.70 mm SL; c, juvenile, MNRJ 38463, 51.18 mm SL; d, male, UFRGS 17543, 86.47 mm SL.

Fig. 7. Rio Doce drainage with the distribution of Deuterodon pedri, southeastern Brazil. The star indicates the type locality.