A new species of Hypostomus Lacépède , 1803 ( Siluriformes : Loricariidae ) from the rio Tocantins-Araguaia basin , Brazil

Hypostomus delimai is described from the rio Tocantins, Tocantins State, and from the rio Araguaia, Pará, and Tocantins States, Brazil. The new species is distinguished from all other Hypostomus species, except from H. carinatus, H. hoplonites, and H. watwata, by the presence of five to eight (mode seven) predorsal plates limiting posterior border of the supraoccipital bone (vs. one to three plates). It can be distinguished from H. carinatus, H. hoplonites, and H. watwata by having pale spots over darker background on body and fins (vs. dark spots over lighter background). The species was only found in the middle stretches of the rio Tocantins-Araguaia basin. The first collection of specimens assigned to the new species was done in the rio Tocantins before the construction of the Tucuruí dam. Recently additional material was collected in the rio Araguaia, in a habitat that soon will be flooded for the construction of the Santa Isabel hydroelectric power station.


Introduction
The family Loricariidae, with more than 800 valid species (Reis et al., 2003;Froese & Pauly, 2012), represents one of the largest fish families in the world.Seven subfamilies of Loricariidae are currently recognized: Delturinae, Hypoptopomatinae, Hypostominae, Lithogeneinae, Loricariinae, Neoplecostominae, and Otothyrinae (Reis et al., 2006;Chiachio et al., 2008).The subfamily Hypostominae was reviewed by Armbruster (2004), who excluded several genera formerly considered in the subfamily and proposed Ancistrinae to be a tribe (Ancistrini) within Hypostominae.Hypostomus Lacépède, 1803, with 128 species (Zawadzki et al., 2010;Martins et al., 2012), is the most species-rich genus of this group and one of the largest genera in the Neotropical region.Species of Hypostomus occur almost everywhere in tropical East Andean and southern temperate regions of South America and they colonize nearly any aquatic habitat, although preferring running waters (Montoya-Burgos, 2003).
Four species of Hypostomus were described from the rio Araguaia basin.Hypostomus asperatus Castelnau, 1855 has a large and flat head and spiny spotless body, although a drawing representation of the species shows some dark spots on the dorsal fin (Castelnau, 1855;fig. 2 plate 20).Hypostomus atropinnis (Eigenmann & Eigenmann, 1880) and H. goyazensis (Regan, 1904) are two species that do not have spots nor developed keels along lateral series of plates.Both species are from the rio Vermelho, a tributary to upper stretches of the rio Araguaia (Eigenmann & Eigenmann, 1880;Regan, 1904).More recently, Hypostomus faveolus Zawadzki, Birindelli & Lima, 2008, a honeycomb-spotted species was described from the rio Araguaia-Tocantins and rio Xingu basins (Zawadzki et al., 2008).
In recent surveys in the middle stretches of the rio Araguaia, four pale-spotted specimens of an undescribed species of Hypostomus were collected.Besides, these specimens showed an unusual combination of characters as a complex pattern of platelets limiting posterior border of the supraoccipital, keeled lateral series of plates, and a large interorbital width.Shortly after those collections, several additional specimens from the rio Tocantins collected during the construction of the Tucuruí Reservoir (1980's) were found at the fish collection of the Instituto Nacional de Pesquisas da Amazônia (INPA).The aim of the present work is to describe a new species of the genus Hypostomus based on those specimens.

Material and Methods
Measurements and counts of bilaterally symmetrical features were taken from the left side of the body, whenever possible.Nomenclature of body plates follows Schaefer (1997) and measurements follow Boeseman (1968), modified by Weber (1986), with addition of: lower lip widest width (at maxillary barbel insertion) and lower lip length (at midline between the dentaries, just posterior the dentary rami to the distal border of the lip).All measurements were taken point to point with digital caliper to the nearest 0.1 mm.process deep in lateral view, usually deeper than longer, its upper border convex.Supraoccipital generally with conspicuous median ridge; with narrow and relatively long posterior process limited by five to eight (mode seven) predorsal plates.Plates limiting supraoccipital as part of complex arrangement of platelets (Fig. 3).Dorsal and lateral surface of head and body covered with dermal plates, except for small unplated area on tip of snout and dorsal-fin base.ray curved inward; when adpressed surpassing anal-fin unbranched-ray base; its border slightly rounded.Anal fin i,4; when adpressed, distal tip of posterior rays reaching seventh or eighth plate posterior to anal-fin origin.Caudal fin i,7+7,i; slightly emarginated, with ventral lobe equal to slightly longer than dorsal lobe.
Color in alcohol.Ground color of dorsal surface of head and body grayish-brown.Head, dorsum and flanks covered with many pale spots against darker background.Pale spots dense, small, close to each other and less numerous, larger and more distant to each other from compound pterotic to caudal peduncle (Figs. 2 and 4).On flanks of some individuals pale spots with irregular format usually fused to each other, sometimes forming vermiculations (Fig. 1).Ventral region of head and abdomen slightly lighter than dorsal region in specimens up to 100.0 mm SL, in larger specimens ventral region of body similar to dorsal region.Some larger specimens with upper and lower lip dark.Dorsal, pectoral, pelvic, anal and caudal fins dark brown with pale round spots mainly over rays.Adipose fin dark brown with pale spots sometimes fused along spine (Figs. 1 and 5).

Color in life.
Color pattern similar to that observed in preserved specimens, except body and fins exhibiting greenbrown background and tan spots with green tinge (Fig. 2).Etymology.The specific epithet delimai is in honor of Flávio César Thadeo de Lima, Brazilian ichthyologist, due to his numerous contributions to Neotropical ichthyology.

Discussion
Hypostomus delimai is distinguished from its congeners by an unusual combination of characters, namely, five to eight plates limiting supraoccipital, pale spots and vermiculations over body and fins, keeled lateral series of plates, and a large interorbital width.The three nominal species of Hypostomus having more than three platelets limiting posterior border of the supraoccipital are H. carinatus, H. hoplonites, and H. watwata.Besides the different color pattern H. delimai differs from H. carinatus by having the caudal-fin lobes evenly pigmented (vs.ventral lobe darker than dorsal), and by having the caudal fin slightly emarginated (vs.caudal fin strongly emarginated); and from H. watwata by having the unbranched caudal-fin rays shorter and similar in length to the head length (vs.unbranched caudal-fin rays longer and similar in length to the predorsal distance), and by having shorter caudal peduncle, 25.9-29.7% of SL (vs.longer caudal peduncle, 31.2-35.7% of SL; data from Boeseman, 1968;table 15).
Hypostomus delimai is morphologically most similar to H. hoplonites, although they are differentiated by color pattern.Hypostomus delimai has dark brown background with pale spots on head and body, while H. hoplonites has pale background with dark brown spots (Fig. 5).The new species is further distinguished from H. hoplonites by a straight dorsal-fin distal border (vs.distal border convex), and by the dorsal and ventral unbranched caudal-fin rays similar in length (vs.ventral unbranched caudal-fin ray remarkably longer than dorsal one).Although not very common, considering the high number of species within the genus, overall morphological similarity between a pair of species but with reversion of the color pattern is sometimes observed as: the pale-spotted H. albopunctatus (Regan, 1908)  Considering the developed keels, the Amazonian species of Hypostomus with keels along the lateral series of plates are mainly known from the H. cochliodon species-group, such as H. ericius Armbruster, 2003 andH. oculeus (Fowler, 1943), or belong to the H. plecostomus species-group, such as H. plecostomus and H. faveolus.The new species can easily be differentiated from H. ericius and H. oculeus by its viliform bicuspid teeth vs. the cochleariform teeth shared among members of the H. cochliodon group.The new species can be differentiated from the Hypostomus cf.plecostomus specimens from the Amazon basin by having pale spots instead of dark ones, hypertrophied rows of odontodes on keels of the lateral series of plates vs. moderate rows of odontodes on keels, and a large interorbital width (46.4-54.0% of HL) vs. moderate (36.3-47.6% of HL;data from Boeseman, 1968; Table 1).Zawadzki et al. (2008) described a pale-spotted species, Hypostomus faveolus, from the upper stretches of the Tocantins, Araguaia and Xingu rivers.Hypostomus delimai is mainly distinguishable from H. faveolus by having five to eight (mode seven) plates limiting the posterior region of the supraoccipital vs. one to three large interorbital width (46.4-54.0% of HL) vs. moderate (36.2-46.9% of HL; data from Zawadzki et al., 2008; Table 1), and a roundish to vermiculate pattern of the pale spots vs. a marbled (honey-combed) pattern.
Considering that Hypostomus delimai was collected only in two stretches of the rio Tocantins-Araguaia basin before impoundment processes (Tucuruí Reservoir of rio Tocantins and Santa Isabel Reservoir of rio Araguaia), its adaptability to lentic conditions is questionable.To date, there is not any reference of impact of hydroelectrics dams on the behavior of fast water dwelling loricariids, which are now forced to live in these new lentic environments.An effect of dam constructions on the reproductive success and recruitment of species formerly inhabiting lotic environments has been studied in other Neotropical fish in other river systems (Agostinho et al., 2007;Dei Tos et al., 2009).Changes in several biotic factors such as food resources (Hahn et al., 1997;Rodriguez-Ruiz, 1998), reproduction sites (Suzuki & Agostinho, 1997), and presence or abundance of prey and/or predators (Gilliam et al., 1993;Gilliam & Fraser, 2001;Petry et al., 2010), can negatively influence the population dynamics of rheophilic fish inhabiting reservoirs.Those negative impacts could also affect the populations of H. delimai; but for effective conservation first a thorough study of the biology of this species is necessary.
Distribution and habitat.The species was found only in middle stretches of the rio Tocantins-Araguaia basin (Fig.4).Records of the new species were done before the construction of Tucuruí dam in the rio Tocantins and in the rio Araguaia, in a habitat that soon will be flooded by the construction of the Santa Isabel dam.The rio Araguaia has about 2,627 km long, and its headwaters are located near the Emas National Park, southeast of the Goiás State, Brazil.The rio Araguaia flows northeast to a junction with the rio Tocantins near the town of São João do Araguaia in the State of Pará.These rivers have turbid water, rocky and sandy substrate, and variable remnant riparian vegetation.The new species was found cooccurring, with Squaliforma cf.emarginata (Valenciennes, 1840), Hypostomus faveolus, Hypostomus cf.plecostomus (Linnaeus, 1758), H. pyrineusi(Miranda Ribeiro, 1920), and another putative undescribed species of Hypostomus.
and the dark-spotted H. heraldoi Zawadzki, Weber & Pavanelli, 2008, both sharing the exclusive character of unbranched pelvic-fin spines equal to or longer than the pectoral-fin spines; the dark-spotted H. denticulatus Zawadzki, Weber & Pavanelli, 2008 and the pale-spotted H. multidens Jerep, Shibatta & Zawadzki, 2007, both sharing the exclusive character of symmetrical bicuspid teeth.The inverse color phenomenon can also be seen in the dark-spotted H. plecostomus and the honeycomb-colored H. faveolus, both very similar species from the rio Amazon basin.
Based on holotype and 21 paratypes.Counts and measurements in Table1.Head broad and slightly compressed.Body width at cleithral region slightly greater than head depth and approximately equal to head length.Snout and anterior profile of head weakly rounded in dorsal view.Snout in lateral profile rising from horizontal at approximately 45º.Dorsal profile nearly straight rising from snout tip to interorbital area, then rising slightly convex to dorsal-fin origin; sloped downward from dorsal-fin origin to region of dorsal procurrent caudal-fin rays, then elevating again to caudal-fin origin.Caudal peduncle somewhat ellipsoid in cross-section, dorsally and ventrally flattened.
Eye moderate in diameter (14.1-17.1% of HL), dorsolaterally positioned.Interorbital area wide and flat in frontal view.Mesethmoid forming inconspicuous median ridge on dorsal region of snout.Weak ridge on dorsal surface of head, from nares to upper margin of eyes, and from here to compound pterotic.Cheek plates with odontodes usually small, but sometimes distinctively larger on posterior border.Cleithral

Table 1 .
Predorsal region flattened, with paired moderate ridges.Trunk covered by five lateral series of dermal plates.Dorsal series of plates keeled from dorsal-fin origin to adipose-fin origin, then weakly keeled until upper procurrent caudal-fin rays.papilla with distal portion usually fringed.Lips wide and round.Outer edge of upper lips with odontodes.Lower lip far from reaching gill opening, its inner surface covered with numerous small papillae, larger proximally.Maxillary barbel moderate in size, slightly shorter than orbital diameter.Teeth slender, with elongated main cusp and smaller lateral cusp.Intermandibular tooth row angle approximately from 100° to 120°.Lower surface of head totally covered by platelets except area just beneath lower lip.Pectoral bridge and abdomen totally covered by platelets except small area at base of left and right pelvic-fin unbranched rays, respectively.Dorsal fin II,7; moderate in size; spine flexible; its border almost straight; posteriorly reaching spine of adipose fin.Adipose-fin spine well developed, curved inward, with distal tip usually reaching anteriormost dorsal procurrent ray.Pectoral fin I,6; spine not flexible, slightly curved, with rounded tip, and usually with hypertrophied odontodes, largest on distal portion in largest specimens; when adpressed almost reaching middle of pelvic-fin spine.Pelvic fin i,5; unbranched Morphometric data and counts of Hypostomus delimai.SD = Standard Deviation.