Tometes camunani ( Characiformes : Serrasalmidae ) , a new species of phytophagous fish from the Guiana Shield , rio Trombetas basin , Brazil

A new species of Serrasalmidae, Tometes camunani, is described from the upper drainages of the rio Trombetas basin, Pará State, Brazil. The new species is distinguished from its congeners by having neurocranium with a slight concavity at the level of the frontal bone (vs. concavity absent, dorsal profile of neurocranium straight). It can be further distinguished from its congeners by having teeth with central cusp taller and acute (vs. central cusp shorter and with rounded edge in T. trilobatus), a terminal mouth (vs. upturned mouth in T. lebaili), and 12-26 prepelvic spines (vs. 0-9 in T. makue). The new species is strictly rheophilic like other species of Tometes, and occurs exclusively in the rapids of shield rivers, complex and fragile biotopes that are threatened by anthropogenic activities. An identification key to the species of the Myleus group is provided.


Introduction
Tometes Valenciennes, 1850 is a genus of large-sized and strictly herbivorous serrasalmid fishes which reach approximately 500 mm SL and a weight of up to 4 kg (Jégu & Keith, 2005).All valid species of Tometes are known from leftbank tributaries of the lower Amazon basin, northeastern coastal rivers of the Guiana Shield, middle and upper rio Negro, and right-bank tributaries of the upper rio Orinoco (Jégu et al., 2002a;Jégu, 2003).Species of Tometes are strictly rheophilic and exclusively inhabit rocky rapids associated with rupestral seedlings of Podostemaceae, their main source of food (Jégu et al., 2002b;Jégu, 2003).Given their habitat hyperspecificity (Brito et al., 2007), species of Tometes are especially vulnerable to the loss of lotic systems, and therefore are greatly threatened by the construction of hydroelectric dams (Junk & Mello, 1990;Jégu & Keith, 2005).In addition, rheophilic serrasalmids (e.g., species of Tometes, Myloplus, and Mylesinus) are very important to the traditional culture of local communities (Pagezy & Jégu, 2002, 2003, 2010).Valenciennes (1850) proposed the genus Tometes, based on its incisiform teeth.Ten years later, based only on information from the literature, Kner (1860) synonymized Tometes trilobatus, type-species of Tometes Valenciennes, 1850, with Myleus setiger, type-species of Myleus Müller & Troschel, 1844 (Jégu & Santos, 2002;Jégu et al., 2002c).However, Jégu et al. (2002c) revalidated both the genus Tometes and its type species after the examination of the type series of Tometes, plus additional specimens attributed to the genus.
Tometes, Myleus, Mylesinus Valenciennes, 1850, andOssubtus Jégu, 1992, comprise a monophyletic assemblage based on morphological data (Jégu, 2004).Considering the same taxa, except the monotypic Ossubtus xinguense, Ortí et al. (2008) confirmed those previous results using molecular data, and also proposed the term Myleus group.Currently, Tometes comprises three valid species, the type species T. trilobatus Valenciennes, 1850, T. makue Jégu, Santos & Belmont-Jégu, 2002, and T. lebaili Jégu, Keith & Belmont-Jégu, 2002.The species of Tometes described herein occurs in sympatry with three other rheophilic serrasalmids, Mylesinus paraschomburgkii Jégu, Santos & Ferreira, 1989, Myleus setiger Müller & Troschel, 1844, and Myloplus rhomboidalis (Cuvier, 1818) in the upper reaches of the rio Trombetas basin, at the site that is planned for construction of the Cachoeira Porteira hydroelectric dam.An identification key to the species of the Myleus group is also provided.Jégu et al. (2002b, c).Measurements were taken point to point to the nearest 0.1 mm with digital calipers, and counts were taken under a stereomicroscope; both were taken from the left side whenever possible.Meristic data are given in the description.The range of counts is followed by the value observed on holotype in parentheses.Measurements of the body are given as percentages of Standard Length (SL), and subunits of the head are given as percentages of Head Length (HL).Counts of vertebrae and supraneurals were obtained from examination of two skeletonized (skel.)specimens (MPEG 23448 and MPEG 23449) and radiographs of ten alcohol preserved specimens: MPEG 23440, MPEG 23442, MPEG 23445, MPEG 23446 (3 of 6), MPEG 23447, MPEG 23450 (1 of 2), MPEG 23451 (1 of 2), and ZUEC 7066.Vertebral counts included the Weberian apparatus as four additional vertebrae, and the fused PU1+U1 of the caudal region counted as a single vertebrae.Vertebral counts are categorized into: predorsal vertebrae, which are all vertebrae anterior to the vertical through the first dorsal-fin pterygiophore; postdorsal vertebrae, all vertebrae posterior to the vertical through the last dorsal-fin pterygiophore; the number of vertebrae between the last dorsal-fin pterygiophore and first anal-fin pterygiophore; and the total number of vertebrae.Osteological terminology follows Weitzman (1962).The entire gastrointestinal tract (GIT) from the esophagus to the anus was removed and measured (= GITL ± 1 mm) in eight specimens: MPEG 23448(1), MPEG 23449(1), MPEG 23450(2), MPEG 23451(2), and MPEG 23452(2), 90.8-382.0mm SL.The relative length of the GIT (= RLGIT) was calculated as RLGIT=GITL/SL.Stomach contents were preserved in 70% ethanol solution and examined under a stereomicroscope to identify food items to the lowest taxon possible.

Measurements and counts follow
Institutional Description.Morphometric data is presented in Table 1.Body extremely compressed, overall aspect of body profile ovoid.
Highest body depth at the level of the dorsal-fin origin.Dorsal head profile convex from mouth to vertical line through anterior portion of orbit, from latter point to supraoccipital base with a slight concavity (readily visible in radiography or skeletonized fish), supraoccipital spine straight to slightly convex, and approximately straight from supraoccipital tip to dorsal-fin origin.Dorsal-fin base scarcely convex; body profile straight from posterior end of dorsal-fin base to adipose-fin origin.Ventral profile of head and body (i.e., from lower lip to vertical through anterior portion of orbit and from the latter point to anal-fin origin) slightly convex.Caudal peduncle relatively short, profile of lower caudal peduncle slightly concave.Snout broadly rounded.Mouth terminal to scarcely subterminal, jaws equally sized.Premaxillary teeth in labial row contacting teeth in lingual row.Five teeth in labial row, two teeth in lingual row (Fig. 2c).Premaxilary and dentary teeth incisiform, relatively robust and shorter when compared with the teeth of Ossubtus and Mylesinus, which are slender and taller.Premaxillary teeth 1-3 in labial row, each with sharp edge; teeth 1 and 2 separated by gap (Fig. 2c,d).Premaxillary teeth 4 and 5 in labial row shorter and broader than remaining teeth and with sigmoid edge (Fig. 2c,d).Dentary teeth 5, bito tricuspid, with the anterior cusp larger than posterior cusp; posterior cusp externally overlapping anterior cusp of the next tooth (Fig. 2a).Pair of symphyseal dentary teeth always present behind the main series of teeth.Maxillary edentulous.
Premaxillary lacking interdigitations at symphysis.Ascending premaxillary process elongated, moderately pointed and oblique in relation to antero-posterior axis of bone (Fig. 2d,e).Lateral premaxillary process short, subrectangular and protruding in relation to fifth tooth in labial row to one-third size of tooth (Fig. 2c).Lateral premaxillary process with a concavity where maxillary is inserted (Fig. 2c).Transversal process aligned with fifth tooth in labial series and protruding to one-fifth its size (Fig. 2c).Four replacement teeth trenches on premaxillary (Fig. 2e).Slender dentary, slightly arched, with 4 or 5 bony lamellae at symphysis (Fig. 2a).Antorbital club-shaped, wide anteriorly and lacking sensory canal.Supraorbital with serrated margins on inner and posterior portions.Infraorbitals 1, 5 and 6 with unbranched sensory canal, 2 and 3 with branched sensory canal, and 4 with canal shaped like an inverted Y.
Neurocranium high, triangular, and elongated.Mesethmoid elongated, pointed and triangular anteriorly.Ethmoidal wings elongated, slender antero-posteriorly, positioned on anterior half of mesethmoid.Neurocranium presenting a slight concavity at the level of the frontal.Parietal club-shaped, narrower anteriorly, increasing slightly in width posteriorly.Supraoccipital spine well  developed, thin, dorsal portion slightly curved.Broad orbital region.Supraorbital with anteroventral margin slightly convex and posteroventral axis slightly downturned.Orbitosphenoid with two laterally compressed bony lamellae, anterior process widened distally and upturned.Orbitosphenoid posteroventral process narrow and projecting ventrally.Ventral margin of orbitosphenoid not reaching parasphenoid.Parasphenoid lacking midventral keel, and with a ventral aperture forming two thin projections parallel to each other across the ventral margins of the prootic and basioccipital.Pterotic triangular, with posterior process directed downward.Sphenotic thin with concave ventral margin; anterior portion wide, narrowing posteriorly from middle portion of bone (Fig. 2b).
The gut of T. camunani is long and elaborately coiled.The relative length of gastrointestinal tract (RLGIT=GITL/ SL) ranges between 4.2 and 5.5 times in SL (mean 4.9).

Color in alcohol.
General coloration of body brownish-yellow, darker on dorsal portion.Dorsal, anal and caudal fins hyaline in proximal portion, darker towards margin.Caudal fin with a distal, wide, dark, diffuse band.Adipose fin uniformly brown.Pectoral and pelvic fins hyaline.Juvenile specimens up to 100 mm SL with a round dark blotch at the humeral region (Fig. 3).

Color in life.
Based on observations of freshly preserved specimens: general body color silver, dorsal and anal fins dark-brownish, caudal-fin with a distal, wide, dark band.During the reproductive period, irregularly-shaped red spots evident over flanks, in supracleithrum region and on the anal-fin, mainly in mature males.
Sexual dimorphism.Sexually mature males of Tometes (> 210 mm SL) are characterized by the presence of an additional anal-fin lobe (Jégu et al., 2002c).In T. camunami, the second lobe is centered on branched anal-fin rays 14 to 16.The dorsalfin rays of mature males of T. camunami are also elongated, forming filaments.Irregularly-shaped reddish blotches are present on the body in mature females, but are more conspicuous in mature males.
Based on the presence of the second anal-fin lobe, the smallest mature male of Tometes camunani observed measured 210 mm SL, which is similar to the size of the smallest recorded mature male of T. makue (Jégu et al., 2002b).In contrast, a second analfin lobe is only evident in specimens of Tometes trilobatus and T. lebaili at about 300 mm SL (Jégu et al., 2002a,c).In some mature males of Tometes, the distal portions of the rays of the second anal-fin lobe have a pair of stiff, laterally curved hooks, which is similar to the condition observed in Mylesinus paraschomburgkii (Jégu et al., 1989: fig. 8).Anal-fin rays with stiff hooks were observed in specimens of Tometes trilobatus, T. makue, and T. lebaili at about 400 mm SL (Jégu et al., 2002a,b,c).Similarly-sized mature males of Tometes camunani (MPEG 23448, 382 mm SL;MPEG 23440, 384 mm SL), however, lack stiff laterally curved hooks on second anal-fin lobe.
Etymology.Species refers to "camunani", its common name in the Wai-Wai language.The Wai-Wai inhabit the upper rio Trombetas basin, and consider the species of great cultural importance.The common name is also employed by local quilombolas (i.e., inhabitants of settlements founded by escaped slaves of African origin), who capture the fish using as bait the fruit of the camu-camu tree (Myrciaria dubia, Myrtaceae).
Ecological notes.The diet of the two smallest specimens examined (MPEG 23449 and MPEG 23450; 90.8 and 133 mm SL, respectively) was composed mainly of fragments of Podostemaceae and benthic macroinvertebrates (Leptophlebiidae, Simuliidae and Chironomidae).The largest specimens examined (MPEG 23448;MPEG 23450;MPEG 23451;MPEG 23452;n = 6, 175-382 mm SL) consumed mainly leaves of Podostemaceae, and fragments of grass and whole seeds of Myrtaceae and Fabaceae.Oxyuroid nematodes (Rondonia rondoni) were also found in the gastrointestinal tract of all dissected specimens.

Discussion
All genera of the Myleus group occur exclusively in shield drainages, and are rheophilic and phytophagous, feeding mainly on Podostemaceae (Jégu, 2004).Tometes camunani occurs in association with swift-flowing rapids and rocky outcrops in clear water rivers of the upper rio Trombetas.During the dry season, schools of large specimens (about 300 mm SL) were observed swimming against the current along very shallow stretches of rapids (depth < 0.35 m).
Given the habitat hyperspecificity of Tometes camunani to river stretches with rapids in the rio Trombetas basin, it seems that the slow-flowing lower reaches of this basin and the Rio Amazonas channel are barriers to its dispersal.Based on personal observations of the last author around Cachoeira Porteira during the 2007 low-water period, larval and small juveniles of Mylesinus and Tometes are restricted to within 200 m downstream of the rapids.A high concentration of larval and juvenile specimens of Mylesinus and Tometes was observed within the rapids among leaves of Podostemaceae, suggesting positive rheotropism from a larval stage.As a consequence, the species is likely sensitive to the impacts caused by the construction of hydroelectric dams.Like its congeners and several other serrasalmid genera, T. camunani has a typical "shield" distribution pattern (i.e., restricted to shield areas of northern cis-Andean South America; Lima & Ribeiro, 2011).Considering camunani is poorly understood at present time.Future studies involving molecular analysis of T. camunani and other fishes typical of shield areas are needed to evaluate the roles of dispersal and vicariance in the distributional patterns observed across rivers draining the Brazilian and Guiana Shields.