Anostomoides passionis, Geraldo Mendes dos Santos & Jansen Zuanon, 2006

Geraldo Mendes dos Santos & Jansen Zuanon, 2006, Anostomoides passionis, a new fish species from rio Xingu, Brasil (Characiformes: Anostomidae)., Zootaxa 1168, pp. 59-68 : 61-67

[[ Anostomoides passionis , new species (continued) ]]

Diagnosis

Anostomoides passionis n. sp. is distinguished from the other two congeneric species by the lower lateral line scale count (38-39 versus 39-41 in A. atrianalis and 42-44 in A. laticeps ); premaxillary teeth with straight and smooth borders, without cusps (vs. bicuspidate to somewhat tricuspid in the other two species); and by the color pattern (brownish-grey with two round to heart-shaped dark blotches on the side and deep red fins, vs. three transverse dark bands on the side in A. laticeps and absence of dark blotches or bands on the side in A. atrianalis ).

Description

Refer to Figs. 1 and 2 for a general view of the holotype and one of the paratypes, and to Table 1 for measurements and body proportions. Body deep and laterally compressed. Dorsal profile gently sloped from snout to dorsal fin base; slightly slanted posteroventrally at dorsal fin base, slightly convex between end of dorsal fin base and origin of adipose fin, then gently concave to caudal fin base. Ventral body profile gently curved from tip of lower jaw to pectoral fin insertion, slightly convex to almost straight to anal opening, slanted posterodorsally at anal fin base and somewhat concave at caudal peduncle. Caudal peduncle almost rectangular, slightly longer than high. Post pelvic region compressed but without forming keel.

Dorsal fin with upper margin slightly convex when fully spread; median dorsal fin rays approximately two times longer than first and last rays. Dorsal and adipose fins well separated, anterior portion of adipose fin base partially covered with scales. Pectoral fin wide, with convex margin, its tip reaching midway to base of pelvic fin. Pelvic fins wide with round edges, located slightly in advance of mid-body, and well separated from each other when spread. Anal fin with border slanted posterodorsally, its tip surpassing level of hypural joint when adpressed. Caudal fin deeply forked with long and wide lobes with rounded tips. Dorsal fin ii, 10; pectoral fin i, 15-16; pelvic fin i, 8 and anal fin ii, 8-9.

Head stout and approximately conical, laterally compressed and covered with thick skin. Snout conical and relatively long with nasal openings set close together and separated by thin fold of skin. Anterior nare a short tube with posterior flap; posterior nare round with lamellae clearly visible inside. Interorbital distance large (ca. 2.4 times in head length). Eye with free orbital rim, relatively small (contained ca. 5.2 times in head length) and placed low on side of head (orbit’s lower edge located below main longitudinal body axis). Mouth terminal to slightly upturned, with lips fleshy and thick, covered internally with numerous papillae. Lower jaw shorter and set behind anterior margin of upper jaw with mouth closed. Gill rakers short and fleshy, numbering 17-20 on first branchial arch, of which 7-8 are located on epibranchial and 10-12 on hypobranchial.

Teeth incisiform, with borders almost straight, excavated on the inner (lingual) side. Symphyseal teeth larger, wider and showing a slightly convex border, the following ones becoming smaller posteriorly, with truncate border and sometimes with small lateral saliencies forming incipient cusps (Fig. 3). Four teeth in each premaxillary and four in each dentary.

Scales large and cycloid. Lateral line straight with 38-39 perforated scales, the pores ramified and composed of 2-4 divergent, usually independent rami. Six to 6.5 series of scales between the dorsal fin origin and the lateral line and 5.5-6.0 series to the pelvic fin origin. Sixteen series of scales around caudal peduncle; 11-13 irregularly set scales along the space between the dorsal and adipose fins.

Color pattern in alcohol. Background color brownish grey, slightly darker at dorsum. Scales with dark edges and central portion yellowish, forming an incipient reticulate pattern on the body. Two dark blotches on the side, round to heart-shaped, over the lateral line series of scales (one, more conspicuously located at the level of posterior half of dorsal fin, and another at anal fin level); these blotches occupy 2-3 scales horizontally as well as vertically. Caudal fin uniformly yellowish to light grey; anal fin grayish with darker interradial membrane; adipose fin with central portion dark grey, base and free edge yellowish; pelvic fin grey with yellowish edges; dorsal and pectoral fins uniformly light grey.

Live color pattern. Dorsal area olive grey, ventral portion lighter and yellowish. Two black, round to heart-shaped blotches over the lateral line scales, one placed at the level of the anterior portion of dorsal fin, and another at anal fin level. Scales with base and free edge darker than the central area, producing a conspicuous reticulated pattern. Fins red to dark orange, suffused with dark melanophores at the base of dorsal and caudal fins, tip of anal fin and central portion of adipose fin (Fig. 2).

Distribution

Presently known only from rio Xingu, State of Pará.

Ecological notes

All specimens of A. passionis collected in rio Xingu were found in areas with moderate to strong current (up to 0.80 m*sec-1) and bottom substrate composed of sand, pebbles and scattered rocks of various sizes. Partially submerged boulders composed the main landscape at all collecting sites (Fig. 3). On one occasion two specimens were collected side-by-side in a gill net, which suggests that this species may form small groups, at least during the dry season. Local fishermen say that A. passionis may form groups of up to a hundred individuals during the early rainy season, when ripe females are commonly caught.

During snorkeling sessions conducted in the dry season, one of us (JZ) observed a single large specimen of A. passionis swimming among dark recesses among submerged boulders, at a depth up to 2 m. The fish moved slowly among the rocks, foraging in feeding bouts of three to four bites directed to the ceilings of small caves under the boulders or at crevices among rocks. The biting produced a loud rasping sound, clearly audible underwater. Stomach contents of two specimens of A. passionis caught during the low water season were composed mainly of fragments of sponges. On another occasion, one fish was observed in a mixed group of several anostomid species ( Leporinus tigrinus Borodin , L. julii Santos, Jegu & Lima , L. brunneus Myers , L. friderici (Bloch) and Leporellus vittatus (Valenciennes )). Other anostomid fishes observed occupying the large spaces under and among boulders were Leporinus megalepis Guenther , Sartor respectus Myers & Carvalho , Pseudanos sp., Anostomus ternetzi Fernandez-Yepez and Synaptolaemus cingulatus Myers & Fernandez-Yepez . Smaller fishes, mainly individuals of the tetragonopterin Astyanax dnophos Lima & Zuanon , pike cichlids ( Crenicichla spp.) and armored suckermouth catfishes (Loricariidae) also shared the rocky shelters in the rapids.

Anostomoides passionis is locally known as “piau do sarão.” Piau is a common popular name for anostomids, and “ sarão ” is the vernacular name of a plant species of the family Mirtaceae, common in the seasonally flooded margins of small rocky islands in rio Xingu. According to the local fishermen, A. passionis feeds on the fruit of these plants during the early flooding season.

Etymology

From the Latin passio, meaning a feeling, in allusion to the round to heart-shaped dark blotches on the side of the fish, as well as the deep red color of its fins.

Discussion

The genus Anostomoides was proposed by Pellegrin (1908) based on the type species A. atrianalis , described from three specimens collected in 1887 by Chaffanjon in the río Orinoco, Venezuela. Later, Eigenmann (1912) described Schizodontopsis laticeps , based on four specimens collected in British Guiana (Crab Falls and Gluck Island), included subsequently in Anostomoides as A. laticeps . According to Pellegrin’s (1908), Anostomoides is an intermediate genus between Leporinus and Anostomus with a distinct dentition: the upper jaw bears compressed teeth, the median ones bicuspidate and the lateral ones somewhat tricuspid; lower jaw teeth also compressed with straight cutting edges, truncate, not denticulate, as in Leporinus . The teeth in Anostomus are aligned sideto-side, whereas in Leporinus the teeth are arranged in a “stair-like” pattern, with the second tooth placed slightly under the anterior one and so on. Anostomoides presents a “reversed” pattern of teeth arrangement, where each tooth partially covers the anterior one ( Géry, 1961).

Myers (1950) proposed a diagnostic key for the genera of Anostomidae but did not include the genus Anostomoides , arguing that the data supplied by Pellegrin did not present relevant information, despite concluding that the genus proposed by that author was distinct enough to be considered valid. Géry (1961) considered Myers’s (1950) work to be a useful contribution to the knowledge of the anostomids, rendering it one of the best-known fish taxa among South American characins at the time, although the omission of the genus Anostomoides in the identification key was pointed out as a problem. From this standpoint, and based on the three specimens analyzed by Pellegrin, Géry (1961) redescribed Anostomoides atrianalis Pellegrin, 1908 , considering Anostomoides a valid genus after comparing it to Leporinus , Anostomus , Synaptolaemus , and Laemolyta .

According to Mago Leccia (1970), A. atrianalis is one of the 27 anostomid species occurring in Venezuela and in the Orinoco basin. The species is considered rare both in collections and in nature. Anostomoides atrianalis is known only from río Orinoco, in Venezuela, while A. laticeps has been reported in British Guiana (Eigenmann, 1912) and various rivers of the Amazon basin such as the Tocantins (Santos et. al, 1984; Santos & Jégu, 1989), Uatumã (Santos & Jégu, 1996), Jamari (Santos, 1991), Xingu (Zuanon, 1999), Araguaia, Negro, Purus, and Tapajós (pers. obs.). These records indicate that A. laticeps is widespread in the main black- and clear-water tributaries of the Amazon River but does not occur - or is rare - in the white water rivers.

Géry (1961, 1977) and Libert (1996/7) considered Anostomoides to be a sister group of Laemolyta , based on the large adult size (up to 350 mm), compressed body and slightly upturned mouth. Nevertheless, in contrast to species of Laemolyta , which possess delicate and multicuspidate premaxillary teeth and dentary teeth with a straight border, species of Anostomoides have strong incisiform teeth in both jaws with incipient cusps on only a few teeth. In some specimens these cusps are more evident, while in others they are almost imperceptible.

In contrast to the other two species of Anostomoides , A. passionis possesses teeth with straight, smooth borders, without cusps; only occasionally do the intermediate premaxillary teeth show a small salience at the margin but without forming a true cusp. The absence of cusps in the upper jaw teeth seems to reveal similarities of A. passionis with species of the genus Leporinus . However, the slanted and slightly upturned mouth, the fringed lips and the high and compressed body constitute a set of characteristics placing the new species in the genus Anostomoides . Further phylogenetic studies may shed some light on the intrafamilial relationships of the anostomid genera and help to ascertain the proper positioning of the species of the genus Anostomoides .