Acestrocephalus nigrifasciatus, Menezes, 2006

Menezes, Naércio A., 2006, Description of five new species of Acestrocephalus Eigenmann and redescription of A. sardina and A. boehlkei (Characiformes: Characidae), Neotropical Ichthyology 4 (4), pp. 385-400 : 395-397

Acestrocephalus nigrifasciatus , new species Fig. 12

Holotype. MCP 30420 (83 mm SL), Brazil, Mato Grosso: Porto dos Gaúchos, rio Arinos, rio Tapajós basin, 11º31’51"S, 57º25’8"W, by R. E. Reis, L. R. Malabarba, E.H.L. Pereira, V. A. Bertaco & A. R. Cardoso, 19 Jan 2002.

Paratypes. MCP 39930, 9 , 64-93 mm SL, taken with holotype . MZUSP 62845 , 1 , 85 mm SL, Brazil, Mato Grosso, rio Juruena, about 1 kilometer above mouth of rio Arinos , by F.A. Machado et al., 25-26 July 1997 ; MZUSP 62847 , 1 , 63 mm SL, ilha do Túlio, rio Arinos about 3 kilometers before emptying into rio Juruena , by F.A. Machado et alii, 24-25 July 1997 .

Diagnosis. Acestrocephalus nigrifasciatus has the same color pattern ( Fig. 12 ) and eye size ( Fig. 4 ) of A. sardina ( Fig. 3 ), distinct from all other species of Acestrocephalus . A. nigrifasciatus , however, has more scale rows above (13-14 vs 10-12) and below (12-13 vs 10-12) lateral line. The muscular hiatus of the pseudotympanum in A. nigrifasciatus ( Fig. 5e ) is longer and narrower than that of A. sardina ( Fig. 5a ) and the fibers of the obliquus inferioris muscle are not visible as in the latter species.

Description. Morphometrics of holotype and additional specimens presented in Table 12. Body moderately large (SL=64.0-93.0 mm). Body form, dorsal and ventral body profiles, shape of snout and mouth and extension of maxilla as in A. sardina .

Dorsal fin rays ii, 9 in all specimens, n=12, including holotype. Posterior most ray unbranched, n=12. Adipose fin present. Anal-fin rays iv,28 (iv or v, usually iv unbranched, branched rays mean=29, range 27-31, n=12, posterior ray split to its base and counted as 1). Moderately developed anal-fin lobe including anterior unbranched rays and first 6-7 branched rays.Anal fin of six sexually mature males with bilateral hooks on posterior anterior branched rays. One specimen (MCP 30420, 79 mm SL) has the first 15 branched rays bearing hooks. Number of hooks per ray decreasing from anterior most to posterior most rays (8 hooks on first, 17 on second, 7 on seventh, 3 on 13th and 1 on 15th). Pectoral-fin rays i,15 (anterior unbranched rays i, n=12, branched rays mean 14.6, range 14-15, n=12). Posterior tips of longest pectoral-fin rays reaching slightly beyond pelvic-fin origin. Pelvic-fin rays i,7, n=12. No hooks on pelvic-fin rays of sexually mature males. Distal tips of longest pelvic-fin rays reaching anterior border of anus. Principal caudal-fin ray count 10/9, n=12.

Lateral line complete, perforated scales 74 (mean=72.6, range 70-75, n=12). Scale rows above lateral line 13 (men=13.4, range 13-14, n=12). Scale rows below lateral line 13 (mean=12.6, range 12-13, n=12). Scale rows around caudal peduncle 23 (mean=23.1, range=23-24, n=12).

Shape, size and arrangement of teeth on premaxilla, maxilla and dentary as in A. sardina . Outer row small conical teeth on premaxilla 7 (mean=7.2, range 6-8, n=12). Maxillary teeth 41 (mean=42.4, range 40-46, n=12), with no clear tendency to increase in number with an increase in standard length ( Fig. 6 ). Posterior row dentary teeth 31 (mean=30.1, range 27-34, n=12). Inner row dentary teeth 11 (mean=10.2, range 8-12, n=12).

Vertebrae 37 (mean=37.4, range 37-38, n=11). Total number of gill rakers on first gill-arch 8 (mean=7.2, range 7-8, n=12).

Muscular hiatus of pseudotympanum ( Fig. 5f ) reduced, much longer than deep, exposed first pleural rib scarcely visible, second pleural rib slightly more visible, but obliquus inferioris muscle fibers entirely covered by ventral fibers of obliquus superioris.

Color in alcohol. Similar to that of A. sardina , but dark lateral body stripe broader along entire length (compare Figs. 3 and 12 ) darker anteriorly; diffuse dark blotch on mental area of lower jaw less conspicuous.

Distribution. Acestrocephalus nigrifasciatus is known from the rios Arinos and Juruena, and rio Tapajós basin ( Fig. 8 ) in the state of Mato Grosso.

Etymology. The first part of the species name niger is Latin for black and the second part fasciatus is also derived from the Latin word “fascia” meaning band or stripe, in reference to the dark lateral body stripe of this species. Both names are adjectives.

Figures

Fig. 12. Acestrocephalus nigrifasciatus, MCP 30420, holotype, mature male, 83 mm SL, rioArinos, rio Tapajós drainage.

Fig. 4. Scatter plot of eye diameter on head length for specimens of Acestrocephalus sardina, A. boehlkei, A. pallidus, A. nigrifasciatus and A. acutus. Acestrocephalus sardina and A. nigrifiasciatus have larger eye diameters than the other species suggesting the recognition of two species groups with respect to this character (see diagnoses of A. sardina and A. nigrifasciatus).

Fig. 3. Acestrocephalus sardina, MZUSP 81209, 93 mm SL, immature female, rio Tiquié, rio Negro drainage.

Fig. 5. Schematic drawings of external view of muscles covering the anterior portion of the swim bladder inA – Acestrocephalus sardina (MZUSP 29241); B – A. boehlkei (MZUSP 38699); C – A.maculosus (MNRJ 12657); D – A. stigmatus (MZUSP 10422); E – A. nigrifasciatus (MCP 30420); F – A. acutus (MNRJ 17612); G – A. pallidus (MZUSP 73471).Anterior towards left; 1 plr (first pleural rib); 2 plr (second pleural rib); os (obliquus superioris); ls (lateralis superficialis); oi (obliquus inferioris). Not drawn to scale.

Fig. 6. Scatter plot of number of maxillary teeth on standard length for specimens of Acestrocephalus sardina, A. boehlkei. Acestrocephalus nigrifasciatus, A. pallidus, and A. acutus. The figure is not intended to show species differences therefore regression lines were not drawn and regression analyses were not performed. The primary purpose is to express the tendencies of the number of teeth on the maxilla to increase according to an increase in standard length. For the species represented by large number of specimens the data points are widely scattered.

Fig. 8. Map of northern and central South America showing the geographic distribution of the species of Acestrocephalus. Some symbols may represent more than one locality.