Anostomoides passionis

biology_ecology

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 o

Anostomoides passionis, a new fish species from rio Xingu, Brasil (Characiformes: Anostomidae).

description

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

Anostomoides passionis, a new fish species from rio Xingu, Brasil (Characiformes: Anostomidae).

diagnosis

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).

Anostomoides passionis, a new fish species from rio Xingu, Brasil (Characiformes: Anostomidae).

discussion

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 rio 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 (Gery, 1961). Myers (1950) proposed a diagnostic key for the genera of Anostomidae but did not include the genus Anostomoides, arguing that the data

Anostomoides passionis, a new fish species from rio Xingu, Brasil (Characiformes: Anostomidae).