Hemiodus langeanii, Beltrão & Zuanon, 2012

Beltrão, Hélio & Zuanon, Jansen, 2012, Hemiodus langeanii (Characiformes: Hemiodontidae), a new species from rio Amana, rio Maués-Açú drainage, Amazon basin, Brazil, Neotropical Ichthyology 10 (2), pp. 255-262 : 256-259

Hemiodus langeanii , new species

Figs. 1a , 2

Holotype. INPA 31564, 122.4 mm SL, Brazil, Pará State, Itaituba, Floresta Nacional do Amana reserve ( FLONA do Amana), rio Amana , igarapé Porquinho , 05°06’33.0’’S 57°32’08.0’’W, 29 April 2008, H. Beltrão.

Paratypes. (All specimens from Brazil, States of Pará and Amazonas) . INPA 31562 , 8 , 88.8-135.6 mm SL + 1 c&s, 110.5 mm SL (collected with the holotype) ; MZUSP 109438 , 2 , 115.5 - 126.9 mm SL ; MPEG 20035 , 2 , 118.5 - 133.2 mm SL . INPA 31563 , 6 , 89.5-126.9 mm SL, State of Amazonas , in the northern border of the FLONA do Amana, at right margin of rio Amana , 04°46’41.0’’S 57°28’25.0’’W, 6 May 2008, H. Beltrão .

Diagnosis. Hemiodus langeanii differs from its congeners by its high body (27.1-35.3%, mean 32.3% SL, vs. 18.8-28.5% in remaining species, except H. argenteus Pellegrin, 1908 , H. microlepis Kner, 1858 , H. orthonops Eigenmann & Kennedy, 1903 , and H. parnaguae Eigenmann & Henn, 1916 that have values that fall within the limits of variation of new species). Hemiodus langeanii shows a color pattern characterized by absence of conspicuous longitudinal stripe along the body or transverse bands of melanophores that help distinguish it from most species in the genus ( H. thayeria Böhlke, 1955 , H. ternetzi Myers, 1927 , H. tocantinensis Langeani, 1999 , H. quadrimaculatus Pellegrin, 1908 , H. vorderwinckleri (Géry, 1964) , H. huraulti (Géry, 1964) , H. sterni (Géry, 1964) , H. goeldii Steindachner, 1908 , H. atranalis (Fowler, 1940) , H. gracilis Günther, 1864 , H. semitaeniatus Kner, 1858 , H. immaculatus Kner, 1858 and H. jatuarana Langeani, 2004 ). Hemiodus langeanii differs from most similar species ( H. unimaculatus (Bloch, 1794) , H. amazonum (Humboldt, 1821) , H. argenteus , H. microlepis , H. orthonops and H. parnaguae ), with a rounded lateral blotch on the flank and a dark stripe at lower caudal lobe), by its large dark lateral spot equal to, or greater than, the eye diameter (vs. smaller in remaining species except for H. microlepis ) and lateral line scale counts 68-74 (vs. 94-123 in H. argenteus , 124-148 in H. microlepis , 86-99 in H. orthonops , 77-92 in H. parnaguae , and 51-60 in H. amazonum ). Finally, H. langeanii differs from H. unimaculatus (which overlaps in lateral line scale counts) by a higher number of scales between the lateral line and the pelvic-fin origin (9-10), with scales of similar sizes above and below the lateral line (vs. 4- 7, with scales below lateral line larger than those above it in H. unimaculatus ).

Description. Morphometrics and meristics in Table 1. Largest examined specimen 133.3 mm SL. Body relatively short, deep and slightly compressed laterally. Highest body depth at dorsal fin origin. Dorsal profile of body convex to adipose fin and slightly concave from that point to anteriormost dorsal procurrent caudal fin ray. Ventral body profile slanted from snout to origin of pectoral fin, strongly convex from that point to anal-fin, slightly concave between that point to anteriormost ventral procurrent caudal fin ray. Interorbital region slightly concave and greater than snout lenght. Mouth subterminal, not protractile, with 17* (n = 16) or 18 (n = 2) teeth with wide and convex crown harboring 11 cusps. Lower jaw edentulous and anteriorly rounded. Adipose eyelid well developed and covering almost entire eye, except for elongated vertical slit on median portion of pupil. Postorbital length longer than snout length. Branchiostegal rays 4 (n = 18). Gill rakers on epibranchial 34-38 (38*) and on ceratobranchial 47-50 (47*) of first gill arch (n = 4).

Scales cycloid and similar-sized throughout body. Lateral line with 68-74 (73*) perforated scales, 13-15 (14*) scales above and 9-10* below LL series. Cleithrum followed by 4 horizontally elongate scales forming slight elevation above axillar depression. Three scales forming pelvic fin axillary process, last one distinctly elongated; vertebrae 36 (n = 4).

Dorsal-fin rays ii, 9* (one specimen with ii, 10). Pectoral fin rays i, 18* (i, 17-19). Pectoral fin extending halfway to pelvic-fin origin. Pelvic-fin rays i, 10* (i, 11 in one specimen), tip of pelvic fin reaching little beyond halfway to anal-fin origin.Anal-fin rays ii, 10* (ii, 9-11).Anal-fin with distal margin concave. Principal caudal-fin rays 10, 9. Caudal fin with similar sized lobes. Adipose fin teardrop shaped and shorter than eye diameter.

Color in life. Overall body color silvery with dorsum darker. Eyes yellowish with dark chromatophores forming a bar, darker at upper portion of eye. All fins orange tinted. Caudal fin orange, darker in distal portion and with coloration more evident on lower lobe. Black longitudinal stripe along each caudal lobe, with stripe of lower lobe darker ( Fig. 2 ).

Color in alcohol. Overall body color pale brown to yellowish. Lateral spot black and connected to dark stripe of lower caudal lobe by inconspicuous dark midlateral band; in some specimens lateral band extending forward to dorsal portion of operculum. Upper portion of body side with 36 to 39 narrow vertically arranged V-shaped lines (chevrons). Pectoral and pelvic fins hyaline. Dorsal and anal fins with dark chromatophores almost to distal tips. Adipose fin with dark base and light distal edge. Eye with conspicuous bar passing through pupil.

Distribution. Known of the type locality in the rio Amana, rio Maués-Açu drainage, near the boundary of the States of Pará and Amazonas, Brazil ( Fig. 3 ).

Ecological notes. Specimens of Hemiodus langeanii were caught in slow-flowing stretches of the rio Amana and igarapé Porquinho (1.0- 2.5 m deep) and in artificial ponds (4.0-5.0 m deep and 40-70 m in diameter) resulting from goldmining activities. The rio Amana and its tributaries have clear water (not stained by humic acids) but turbid due to excess of fine suspended solids (clay) resulting from mining activities along river margins and/or bottom (dredging). Water at the collecting sites was turbid (vertical transparency 10-21 cm), slightly acidic (pH 6.4-6.8) with a temperature of 25.5-27.7ºC; dissolved oxygen of 6.5-7.3 mg / L and 80-92% of saturation (measurements made between 9:00-11:00 am). Observations of living individuals of Hemiodus langeanii in its habitat revealed that the new species shows benthopelagic habits and was often caught with other characiforms such as Pseudanos sp. , Hoplias malabaricus (Bloch, 1794) , Myloplus sp. and Serrasalmus eigenmanni (Norman, 1929) .

Popular names. In the Brazilian Amazon, species of the genus Hemiodus are referred to as Orana, Cubio, Charuto, and Flecheiro.

Etymology. Named in honour of Dr. Francisco Langeani (researcher at Instituto de Biociências, Letras e Ciências Exatas - Universidade Estadual Paulista “Júlio de Mesquita Filho”-UNESP, Brazil), for his highly relevant contributions to the knowledge of hemiodontid fishes.

Figures

Fig. 1. Lateral view of (a) Hemiodus langeanii, INPA 31564, holotype, 122,4 mm SL, rioAmana, rio Maués-Açú drainage, nearthe boundary of the States of Pará and Amazonas, (b) H. unimaculatus, INPA 25187, 178.0 mm SL (rio Madeira drainage) and (c) H. argenteus,INPA 25897,197.0 mm SL(rio Uatumã drainage).

Fig. 2. Lateral view of Hemiodus langeanii, INPA 31563, paratype, 106.3 mm SL, freshly collected.

Fig. 3. Map of northern South America showing distribution of Hemiodus langeanii(circle) inAmazon basin (05°06’33.0’’S 57°32’08.0’’W).