Hemiodus tucupi Silva & Nogueira & Netto-Ferreira & Akama & Dutra 2020, new species

Hemiodus tucupi, new species

Figs. 1 and 2; Table 2

Hemiodus ternetzi (not Myers)— Camargo et al., 2004: 137 [listed, Rio Xingu basin, based on lot INPA 4284].– Dagosta & de

Pinna, 2017: Appendix I, 163 [in part, occurrence at the upper Rio Xingu obtained from the literature]. Hemiodus thayeria (not Böhlke)— Betancur et al., 2019: 340, fig.4 [live photo of specimen from INPA 43494]. Hemiodus tocantinensis (not Langeani)— Dagosta & de Pinna, 2017: Appendix I, 163 [in part, Rio Iriri and lower Rio Xingu,

based on lots INPA 43589 and INPA 43494].– Dagosta & de Pinna, 2019: 137 [listed, lower Xingu and Iriri rivers].

Holotype. MPEG 36362, 66.5 mm SL, Brazil, Pará, Bacajá at rapids of the Igarapé Bacajaí, Rio Xingu basin, 3°54’37.91”S 51°44’32.78”W, 9 Jun 2015, A. Gonçalves and D. Silva.

Paratypes. All from Brazil, Pará, Rio Xingu basin: ANSP 196907 (9, 45.1–71.8 mm SL), Rio Xingu at mouth of left bank igarapé, 3°07’40.1”S 51°41’27.5”W, 2 Mar 2014, M. Arce and A. Gonçalves. DZSJRP 21378 (1, 91.7 mm SL), Senador José Porfírio, 2°44’54.70”S 52°0’9.50”W, 10 Jul 2014, D. Bastos and A. Gonçalves. DZSJRP 21379, 1+1 CS, 60.7–67.3 mm SL); MPEG 36364 (1 CS, 65.8 mm SL); LIA 2932 (3, 60.8–64.0 mm SL); UFRGS 24771 (1+1 CS, 60.8–67.4 mm SL), same data as holotype. INPA 43494 (1, 62.7mm SL), Rio Xingu (middle Volta Grande), flooded beach & vegetation at upstream point of island in transverse channel of Xingu, ca. 60 km southeast (downstream) of Altamira, 3°35’55.8”S 51°49’57.4”W, 12 Mar 2014, M. Sabaj and L. Rapp Py-Daniel. LIA 438 (1, 75.0 mm SL); MPEG 36363 (2, 61.6–75.9 mm SL), Senador José Porfírio, Rio Bacajaí, 3°49’2.68”S 51°41’4.60”W, 11 Jul 2014, A. Gonçalves and D. Bastos. LIA 676 (1, 73.1 mm SL), Senador José Porfírio, Rio Bacajaí, 3°38’41.71”S 51°45’13.86”W, 12 Jul 2014, A. Gonçalves and D. Bastos. LIA 5841 (2, 70.0- 71.0 mm SL), Vitória do Xingu, stretch with reduced flow at Casa Branca, 3°20’17.23”S 51°45’14.19”W, 12 Aug 2016, J. Santos. MPEG 30422 (4, 52.6–65.1 mm SL), Brasil Novo, unnamed Igarapé close to road, 3°44’45.67”S 52°39’46.33”W, 06 Apr 2013, D. Bastos. MZUSP 123822 (3, 64.3–69.2 mm SL), Brasil Novo, unnamed Igarapé tributary of Rio Iriri, 3°44’45.67”S 52°39’46.33”W, 03 Jul 2015, R. Oliveira. UFRGS 24770 (2, 57.6–77.3 mm SL), Senador José Porfírio, Rio Bacajaí, 3°38’41.71”S 51°45’13.86”W, 12 Jul 2014, A. Gonçalves and D. Bastos.

Non-type specimen. INPA 4284 (1, 33.7 mm SL), Brazil, Pará, Altamira, Rio Xingu, 3°12’S 52°12’W, 08 Oct 1990, L. Rapp Py-Daniel and J. Zuanon.

Diagnosis. Hemiodus tucupi can be readily distinguished from its congeners, except H. ternetzi, H. thayeria and H. tocantinensis, by the presence of a conspicuous, dark longitudinal stripe extending from the postorbital portion of the head to the tip of the lower lobe of the caudal fin (vs. stripe absent or inconspicuous, originating near the vertical through the dorsal fin to the end of the lower lobe of the caudal fin in H. amazonum Humboldt, H. argenteus Pellegrin, H. bimaculatus Nogueira, Langeani & Netto-Ferreira, H. huraulti Géry, H. immaculatus Kner, H. iratapuru Langeani & Moreira, H. jatuarana Langeani, H. langeanii Beltrão & Zuanon, H. microlepis Kner, H. orthonops Eigenmann, H. parnaguae Eigenmann, H. quadrimaculatus Pellegrin, H. sterni Géry, H. vorderwinkleri Géry and H. unimaculatus Bloch; or stripe conspicuous originating near vertical through the dorsal-fin origin to the end of the lower lobe of the caudal fin in H. atranalis Fowler, H. gracilis Günther, H. goeldii Steindachner and H. semitaeniatus Kner). The new species is diagnosed from H. ternetzi and H. thayeria by the presence of an oblique dorsal-fin blotch (vs. blotch absent). It also differs from H. thayeria and H. tocantinensis by the higher number of circumpeduncular scales (17–20 vs. 16, and 14–16, respectively—Table 1), the higher number of perforated lateral line scales (58–66 vs. 46–49 and 51–58, respectively—Table 1), and the higher number of scale rows above lateral line (9–11 vs. 6–8, and 8–9, respectively—Table 1). Additionally, Hemiodus tucupi differs from H. thayeria by the dark longitudinal stripe being extending from behind the eye throughout the body (vs. restricted to the body). Hemiodus tucupi also differs from H. ternetzi by the number of gill rakers on first branchial arch (26–30 vs. 33–35).

Description. Morphometric data for the holotype and 25 paratypes presented in Table 2. Body elongate, fusiform and laterally compressed. Highest body depth at dorsal-fin origin. Head profile pointed anteriorly. Dorsal profile of body convex from tip of snout to adipose-fin origin; concave from that point to insertion of anteriormost dorsal caudal-fin procurrent ray. Ventral profile of body convex from tip of snout to anal-fin terminus, and nearly straight from that point to insertion of anteriormost ventral caudal-fin procurrent ray. Prepelvic region smoothly flattened transversely, postpelvic rounded.

Mouth subterminal. Lower jaw edentulous and rounded anteriorly in ventral view. Upper jaw not protractile. Teeth 8(19) or 9*(7) with distinctly convex border and 6–12 cusps (2). Premaxillary with 4(3) teeth, one tooth inserted between premaxillary and maxillary (3), and maxillary with 3(3) teeth. All teeth forming continuous single cutting edge. Anterior nostril circular, near midpoint between snout tip and anterior margin of eye. Posterior nostril crescent-shaped. Adipose eyelid well developed, covering eye almost entirely, except for vertically elongate opening overlying pupil. Branchiostegal rays 4(3). Gill rakers on epibranchial 8(1) or 11(2), between epibranchial and ceratobranchial 1(2), and on ceratobranchial 17(1), 18(1) or 19(1) of first gill arch.

Scales cycloid, equal in size above and below the lateral line. Lateral line longitudinal series with 58(1), 59*(2), 60(6), 61(3), 62(1), 63(5), 64(1) or 66(2) perforated scales. Cleithrum followed by three or four horizontally elongated scales forming small protuberance above axillary depression into which proximal portion of first pectoral ray fits. Scales rows between lateral line series and dorsal fin 9*(5), 10(15) or 11(2). Scales rows between lateral line series and pelvic-fin insertion 4(3), 5*(18) or 6(1). Postdorsal scales 18(2), 19*(6), 20(6) or 21(8). Circumpeduncular scales 17*(6), 18(3), 19(9) or 20(4).

Pectoral fin pointed distally with i,15(4), i,16*(14) or i,17(8) rays; tip of adpressed pectoral fin reaching vertical through 12 th scale of lateral line longitudinal series. Supraneurals 9 (2), anterior to neural spines of centra 4 to 12. Anteriormost dorsal-fin pterygiophore inserted immediately posterior to neural spine of 12 th (2) vertebra. Dorsal fin pointed distally with ii,9*(26) rays pterygiophores; first unbranched ray nearly half length of second unbranched ray, second unbranched ray and first to fourth branched rays distinctly longer than posterior ones, subsequent rays gradually decreasing in size. First dorsal-fin pterygiophore inserted immediately anterior to haemal spine of 14 th (4) vertebra. Pelvic fin emarginate with i,10*(26) rays. Pelvic-fin origin at vertical through third or fourth branched dorsal-fin ray. Tip of adpressed pelvic fin falling far short of anus. Expanded anal fin nearly triangular, with iii,8*(26) rays, first unbranched ray tiny, second unbranched ray about one-third length of third unbranched, first branched ray longest, subsequent branched rays gradually decreasing in size. Anal-fin pterygiophores 9*(3); first inserted immediately anterior to haemal spine of 29 th (1) or 30 th (3) vertebrae. Adipose fin present. Caudal fin forked with both lobes somewhat pointed; caudal-fin rays i,9/i,8*(26) rays. Dorsal caudal-fin procurrent rays 7(1) or 8(2); ventral caudal-fin procurrent rays 6(1) or 7(1). Total vertebrae 40(2), 41(5) or 42(2). Precaudal vertebrae 27(1), 28(2) or 29(3), caudal vertebrae 12(2), 13(3) or 14(1).

Coloration in alcohol. Ground color of body and head tan. Dorsal area of head light brown. Ventral portion of head light yellow. Body scales of mid-dorsal row and six to eight adjacent longitudinal series light brown near focus with clear margins. Lateral surface of body with black midlateral longitudinal stripe from supracleithrum to ventral lobe of caudal fin, connected to the postorbital pigmentation of head; stripe 3 or 4 scales deep. Four transverse bars variably marked on body. First, anteriormost bar immediately posterior to head, near humeral region; second near vertical through distal tip of adpressed pectoral fin; third between vertical through pelvic-fin median portion and tip; fourth near vertical through anal-fin origin.

Dorsal fin with oblique black blotch extending from mid-distal portion of second unbranched ray towards base of posteriormost 2 or 3 branched fin rays. Pectoral and pelvic fins with few, scattered chromatophores. Anal fin either covered by sparse chromatophores (Fig. 2), or with conspicuous band from middle of anterior rays to base of last rays (Fig. 1). Adipose fin hyaline. Caudal fin with black stripe on its lower lobe, and chromatophores more concentrated on distal portion of lower lobe.

Coloration in life. Based on a picture of one paratype (INPA 43494), taken immediately after fixation (Fig. 2). Ground coloration of body and head plumbeous, gradually becoming more clear to white-silvery ventrally. Dorsolateral area progressively yellowish from adipose fin towards insertion of anteriormost dorsal caudal-fin procurrent ray. Black midlateral longitudinal stripe more conspicuous in life extending anteriorly to anterior portion of snout. Dorsal fin with oblique black blotch extending from its middle basal portion of fin through anterior distal portion. Area anterior to oblique blotch yellowish. Adipose fin yellowish. Pectoral-fin origin yellowish becoming gradually hyaline distally. Pelvic and anal fins hyaline. Caudal fin overall yellowish.

Distribution. Hemiodus tucupi is known from the lower Rio Xingu and its tributaries: Rio Iriri, Rio Bacajá and Rio Bacajaí, Amazon basin, Pará state, Brazil (Fig. 3).

Etymology. The specific name tucupi is given in reference to the in vivo coloration of Hemiodus tucupi, which presents pale yellow fins, in allusion to the similarly colored juice taken from the root of the manioc (Manihot esculenta Crantz), the “tucupi”. It is a widely used ingredient of the Amazonic cousine, present in several traditional dishes. A noun in apposition.

Conservation status. The Rio Xingu was recently impacted by the construction of the Belo Monte Dam at the Volta Grande area, drastically reducing its flow downstream, and changing the water dynamics upstream. Considering the distribution of H. tucupi, the Belo Monte Dam is a plausible impact for the species population by shifting the habitat both in the rapids and the flooded area. On the other hand, the species occurs in at least three tributaries of the Rio Xingu, two of them only indirectly affected by the Belo Monte Dam. Thus, Hemiodus tucupi could be classified as Least Concern (LC), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019).