Astyanax xavante

biology_ecology

Habitat and ecological notes. Astyanax xavante inhabits crystalline water streams with flow from 0.05 to 0.70 m 3 / s. There is a reduced number of pools along these watercourses, but there are many rapids and accentuated falls, some up to 30 m high. The bottom of the rapids is generally composed of stone and gravel-stone. Sand and small silt and clay fractions prevail at the bottom of the pools. In general, the rapids are typical of mountain streams with fast-flowing water and gravel, rocky, and sandy bottoms. The banks are covered by riparian forest which prevents most light penetration and have little or no marginal herbaceous vegetation. There are many exposed roots from erosion and many tree trunks, branches and submerged leaves, in various stages of decomposition. The fishes preferentially occupy the water surface and the spaces among roots and branches. They usually form schools with up to two dozen individuals, but schools with about 150 individuals have also been observed. They are more abundant in the upper and middle courses of the córrego Avoadeira, and their frequency decreases downstream. Astyanax xavante is seemingly the only species inhabiting above the cachoeira Pé

Astyanax xavante, a new species of characid from middle rio Araguaia in the Cerrado region, Central Brazil (Characiformes: Characidae)

description

Description. Morphometric and meristic data of holotype and paratypes presented in Table 1. Larger specimen 59.6 mm SL. Body compressed and elongate; larger depth in about two to three scales ahead of dorsal-fin origin. Preventral and predorsal areas rounded. Dorsal and ventral body portions unequal, first shallower when verified by imaginary horizontal line passing through buccal opening. Dorsal profile straight between snout and occipital process; slightly convex from this point to base of dorsal-fin origin; straight from there to caudal-fin, slightly concave at limits of dorsal and adipose fins. Ventral profile smoothly convex from snout up to slightly behind pectoral-fin origin; straight from that point to anal-fin origin; straight at base of anal fin and straight from there to caudal fin. Mouth terminal and horizontal. Snout smaller than eye diameter. Upper jaw slightly longer than lower jaw. Upper jaw larger than orbital diameter. Dorsal-fin origin at middle or posterior to middle of standard length; when adpressed its distal extremity reaches fourth scale anterior to adipose-fin origin; distal border smoothly rounded; ii, 9 rays. Caudal fin naked and forked, with symmetric o

Astyanax xavante, a new species of characid from middle rio Araguaia in the Cerrado region, Central Brazil (Characiformes: Characidae)

diagnosis

Diagnosis. From the species assigned to the Araguaia-Tocantins basin, Astyanax xavante differs readily by having humeral spot vertically elongated vs. horizontally oval in A. argyrimarginatus, A. asuncionensis, A. goyacensis, A. kullanderi, A. novae, A. unitaeniatus, and other undescribed forms of the Astyanax bimaculatus species complex; fewer lateral-line scales, 34 - 37 vs. more than 48 in A. elachylepis and A. symmetricus; larger body depth, 35.5 - 40.2 vs. 25.0 - 28.6 % of SL in A. gracilior; more anal-fin rays, 23 - 26 vs. 18 - 19 in A. scintillans; and fewer maxillary teeth, 1 - 3 vs. 4 - 7 in A. guianensis. Astyanax xavante is distinguished from all other congeners by the following combination of characters: two vertical, brown humeral spots, a brown stripe on the flank, a black spot on the middle caudal-fin rays, 19 to 23 branched anal-fin rays, 34 to 37 perforated scales on lateral line, larger body depth (35.5 - 40.2 % of SL) in about two to three scales ahead of dorsal-fin origin, head length 28.4 - 31.2 % of SL, head not massive, interorbital width 34.5 - 39.4 % of HL, snout not abruptly tapered, distance from snout to origin of dorsal fin 50.0 - 56.0 % of SL, one to t

Astyanax xavante, a new species of characid from middle rio Araguaia in the Cerrado region, Central Brazil (Characiformes: Characidae)

distribution

Geographical distribution. Known from the type locality, córrego Avoadeira, a middle rio Araguaia tributary located in the Parque Estadual da Serra Azul, Barra do Garças, Mato Grosso. Serra Azul is located in the extreme south of the Serra do Roncador, at the beginning of the great Central Brazilian Plateau, whose direction is mainly south-north.

Astyanax xavante, a new species of characid from middle rio Araguaia in the Cerrado region, Central Brazil (Characiformes: Characidae)