Geographic distribution of Hemigrammus ora ( Ostariophysi : Characiformes : Characidae ) in the Amazon basin , Brazil

New records of Hemigrammus ora Zarske, Le Bail & Géry, 2006, previously believed to be endemic to the French Guiana drainages, are confirmed for Brazilian drainages. The species is reported from the Tocantins-Araguaia system and lower Amazon River. Morphometric and meristic data, previously undescribed morphological traits related to caudal-fin squamation and anal-fin hooks, and geographic variation are presented for the species.

In a recent expedition to the headwater streams of the Araguaia River in the states of Mato Grosso and Goiás, Brazil, specimens of Hemigrammus were collected, and after of examination, they were identified as Hemigrammus ora Zarske, Le Bail & Géry, 2006.Hemigrammus ora is a small characid species originally described from low land rivers in the French Guiana.Material deposited in scientific collections, identified as Hemigrammus sp., has revealed that the species was previously collected in some other localities in the Araguaia-Tocantins River basin and other tributaries of the lower Amazon basin.
In this study, meristic and morphometric data were obtained following FINK & WEITZMAN (1974), with the addition of the following features: head depth, measured at the vertical through the posterior tip of the supraoccipital process; dorsalfin base length; longest anal-fin ray length; anal-fin base length; and dorsal to adipose fin distance, measured from the posterior end of dorsal-fin base to origin of the adipose fin.The measurements, snout and upper jaw lengths, were also taken according to the methodology of GÉRY (1972), following ZARSKE et al. (2006), herein emphasized by an asterisk (*).Measurements were per-formed with a caliper to the nearest 0.05 mm on the left side of the specimens.Body measurements are presented as percents of standard length (SL), and measurements on the head are presented as percents of head length (HL) and standard length, for comparison with the original description of H. ora.Counts of supraneurals, gill rakers on the first branchial arch, branchiostegal rays, vertebrae, and procurrent caudal-fin rays were taken on five cleared and stained (c&s) specimens prepared according to other Hemigrammus species (ZARSKE et al. 2006).Additionally, ZARSKE et al. (2006) quoted as diagnostic of H. ora the arrangement of the cusps of the premaxillary teeth of the inner row, in a crescent line; 21 to 24 branched anal-fin rays; 32 to 33 lateral line scales; 10 to 15 perforated scales on the lateral line; body depth 2.94 to 3.44 in SL; and head length 3.42 to 3.96 in SL.
The toothless maxilla found in H. ora is an uncommon condition among the species of Hemigrammus, as well as its shape (not illustrated in the original description) (Fig. 5).Most species of Hemigrammus have at least one maxillary tooth, and the maxilla is mostly flat along its axis, with a short anterior cylindrical rod-like process medially directed, which is connected through ligaments to the premaxilla and lateral process of the mesethmoid.In H. ora, the maxilla is proportionally reduced in length when compared with any other species of Hemigrammus.It is cylindrical along most of its axis, and only the posterior portion is lamellar.Hemigrammus ora has scales on the caudal fin covering one-third of the dorsal lobe and half length to two-thirds of the lower lobe, a condition found in most species of Hemigrammus (see CARVALHO et al. 2010, fig. 3b).This feature was not mentioned in the original description, but the presence of caudal fin scales can be noticed in the picture of the paratype (ZARSKE et al. 2006: 20, fig. 1).Morphometric and meristic data of H. ora specimens from the Tocantins-Araguaia Rivers, low Amazon River, and Xingu River basins are presented in Tables I and II.Measurements and counts from these specimens overlap the diagnostic and descriptive data presented in the original description of H. ora.The only discrepant value was the snout length* 7.7-10.6%SL (versus 3.9-7.0%SL).Among the counts, the only information that diverges from the original description is the number of small dentary teeth, posterior to the first four large teeth.Instead of eight to ten small conical teeth, the five cleared and stained specimens presented three small teeth, and in some instances, the tooth just after the first four was tricuspid.
Regarding the presence of hooks on the anal-fin rays, ZARSKE et al. (2006: 21) briefly mentioned the absence of "hooklets on the first rays of anal fin" of H. ora.LIMA & SOUSA (2009) remarked that they were uncertain about the presence of anal-fin hooks in H. ora, due to the fact that their descriptions were based on a few specimens.Herein, the presence of hooks was evidenced on the anal fin of males.Some (up to 28.7 mm SL) have small bony hooks on all branched pelvic-fin rays, and along the lengths of the last unbranched to the eighteenth branched anal-fin rays.The hooks are small, thin, dorsally arched, and their number varies from seven, on the anteriormost ray, to one, on the posteriormost hook-bearing ray.The size and distribution of hooks on the anal-fin rays of H. ora, differ from the pattern described by LIMA & SOUSA (2009) to their more restrict "Hemigrammus ocellifer species group".LIMA & SOUSA (2009) characterized in this group based on the presence of a single medium-sized hook per anal-fin ray, distributed in the same height of each ray, from the last unbranched to the sixth to seventh branched anal-fin rays.However, the distribution and morphology of the anal-fin hooks in H. ora resembles the pattern that LIMA & SOUSA (2009: fig.6) assigned to Hemigrammus schmardae (Steindachner, 1882).Despite the anal-fin hooks, no other sexual dimorphic feature was found in H. ora.No gill glands were found on the macroscopic examination of the first gill arch of mature male specimens (BURNS & WEITZMAN 1996).ZOOLOGIA 28 (4): 545-550, August, 2011 The specimens of H. ora herein examined present two main morphological differences when compared with the type specimens: a lower number of small dentary teeth posterior to the first four large teeth (3 versus 8-10); and a longer snout (7.7-10.6 versus 3.9-7.0%SL*).Additional material of H. ora from the French Guiana was not found in fish collections.Therefore, we were not able to provide a more extensive investigation concerning those differences.In spite of that, the specimens from Brazil fit the diagnosis elaborated by ZARSKE et al. (2006) based on specimens from the French Guiana, with which they share the color pattern (with distinct humeral and caudal spots), and the morphology of the maxilla, features absent from other species of Hemigrammus.Therefore, we consider the previously mentioned differences between the specimens from Brazil and French Guiana as corresponding to geographic variation.
Hemigrammus ora was described from specimens from the Pripri Yiyi River, a coastal drainage from French Guiana.It was also recorded for the Sinnamary basin based on the geographical range presented by PLANQUETTE et al. (1996) for Hemigrammus aff.schmardae, a misidentification of H. ora (according to ZARSKE et al. 2006).The species was considered to be putatively endemic to those drainages.The geographic distribution of Hemigrammus ora is herein extended to the lower Amazon tributaries, upper Xingu and Tocantins-Araguaia Rivers basins (Fig. 6).Based on these new records, we hypothesize that the species has a continuous distribution from its type locality in French Guiana to the lower Amazon River tributaries, until the upper Tocantins-Araguaia River basin.This distribution pattern, from the French Guiana low land rivers to the lower Amazon River and some Brazilian Shield rivers, is observed in other freshwater species, such as Acnodon spp.

Figure 6 .
Figure 6.New records of H. ora (dots) in Brazil.The type locality of H. ora is represented by a star in French Guiana.Each dot may represent more than one locality.

Table I .
Morphometric data of H. ora, Amazon system, Brazil.Measures taken according to GÉRY (1972) are followed by an (*).

Table II .
Meristic data of H. ora, Amazon system, Brazil.