Acestrocephalus maculosus, 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 : 390-392

Acestrocephalus boehlkei Menezes, 1977 Fig. 9

Acestrocephalus boehlkei Menezes, 1977: 186 , fig. 1 (original description, type locality: Río Punino , tributary of Río Payamino (Napo River system), above Coca, Ecuador).

Material examined. MCZ 51473, holotype, 135 mm SL (radiograph examined), Ecuador: Río Punino, tributary of Río Payamino, Río Napo system, by T. Roberts and Parker, 25-27 November 1971 ; MZUSP 12993-94 , 2 , paratypes 85-116 mm SL, taken with holotype ; MZUSP 12995 , 1 paratype, 40 mm SL, Río Payamino and tributary 3-4 miles upriver from mouth of Río Payamino into Coca , by T. Roberts, Garcia, Parker and Herrera , 20 November 1971 ; MZUSP 38699 , 2 , 76-87.5 mm SL, Napo: Río Aguarico in Quarumo, Río Napo system, 0º1’S, 76º37.5’W . MZUSP 12996- 98 , 3 , paratypes, 59-85 mm SL, Peru, Huanuco: backwater near Pueblo Novo flowing into Río Tulumayo, by Catherwood Expedition , 27 September 1955 .

Diagnosis. Acestrocephalus boehlkei , A. maculosus sp.n. and A stigmatus sp.n. are the only species of the genus bearing a dark spot at the humeral region ( Figs. 9 , 10 , and 11). Acestrocephalus boehlkei , however, has more anal-fin rays (34-36) than A. maculosus (25-27) and A. stigmatus (29-31) and more scale rows around caudal peduncle (25) than A. maculosus (23) and A. stigmatus (22-23). See tables 4 and 5. Additionally, A. boehlkei differs at once from A. maculosus and A. stigmatus in number of perforated lateral line scales (74-78 vs 70-73 in A. stigmatus and 71-73 in A. maculosus ) and in number of small conical teeth between anterior and posterior canines of outer row premaxillary teeth(10-12 vs 7-9 in both A. stigmatus and A. maculosus (see Tables 6 and 7). The muscular hiatus of the pseudotympanum in A. boehlkei ( Fig. 5b ) is also wider than those of A. maculosus ( Fig. 5c ) and A. stigmatus ( Fig. 5d ).

Description. Morphometrics of holotype and additional specimens presented in table 8. Meristic and morphometric data based on all examined lots of this species because no statistical differences found among them. Body moderately large (SL=31.5-135.0 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=21, including holotype. Posterior most ray unbranched, n =21. Adipose fin present. Anal-fin rays v,34 (iv or v, usually v unbranched, branched rays mean=34.5, range 33-36, n=21, posterior ray split to its base and counted as 1). Slightly developed anterior anal-fin lobe including anterior unbranched rays and first 9-10 branched rays. Anal fin of three sexually mature males with bilateral hooks on posterior part of anterior branched rays. In a specimen 87.5 mm SL (MZUSP 38699) hooks present on anterior 11 branched rays and number of hooks per ray vary considerably: first branched ray with 9, third with 17, sixth with 24 and eleventh with 8. Pectoral-fin rays i,14 (anterior branched ray i in all specimens, n=21), branched rays mean 14.6, range13-16, n=21. Posterior tips of longest pectoral-fin rays reaching beyond pelvic-fin origin. Pelvic-fin rays i,7, n=21. No hooks on pelvic-fin rays of sexually mature males. Distal tips of longest pelvic-fin rays extending to or slightly beyond posterior border of anus, but not reaching anal-fin origin. Principal caudal-fin ray count 10/9, n=21.

Lateral line complete, perforated scales 74 (mean=76.1, range 74-79, n=21). Scale rows above lateral line 13 (mean=13.5, range 13-15, n=21). Scale rows below lateral line 12 (mean=12.1, range 12-13, n=21). Scale rows around caudal peduncle 25 in all specimens, n=9.

Shape, size and arrangement of teeth on premaxilla, maxilla and dentary as in A. sardina . Outer row small conical teeth on premaxilla 12 (mean=10.1, range 9-12, n=21. Maxillary teeth 44 (mean=37.6, range 32-44, n=21), increasing in number according to increase in standard length ( Fig. 6 ). Posterior row dentary teeth 33 (mean=26.3, range 20-33, n=21), increasing in number ontogenetically ( Fig.7). Inner row dentary teeth 11 (mean=12, range 10-14, n=21).

Vertebrae 39 (mean=39.6, range 39-41, n=9). Total number of gill-rakers on first gill-arch 6 (mean=6.1, range 6-8, n=21).

Arrangement of muscles limiting muscular hiatus of pseudotympanum and degree of exposition of first and second pleural ribs as in A. sardina (compare figs. 5a and 5b).

Color in alcohol. Body light brown to pale yellowish, darker dorsally. Dorsal head and snout more densely pigmented with dark chromatophores compared to lateral part of head. Lateral body stripe broader from below dorsal-fin origin to below adipose-fin origin, narrower from dorsal-fin origin anteriorly to upper opercle and on caudal peduncle, dark color sometimes obscured by guanine. Lateral stripe starts from behind upper opercle extending posteriorly to caudal-fin base where connecting to oblong dark blotch posteriorly extending to middle caudal-fin rays. Irregularly shaped, vertically elongated dark blotch at humeral region over anterior lateral body stripe, vertically above anterior pectoral fin. Mental area of lower jaw with diffuse dark blotch, sometimes unconspicuous or even absent. Small black dot at origin of dorsal-fin origin, extending to first unbranched dorsal-fin ray base. Dorsal, anal, and caudal fin dusky with scattered dark chromatophores along fin rays and membranes. Pectoral and pelvic fins pale with fewer dark chromatophores than other fins.

Distribution. Upper Amazon River basin in tributaries of Río Napo, Ecuador and of Río Putumayo, Peru ( Fig. 8 ).

Remarks. Lasso & Taphorn (1992) reported A. boehlkei from the Ventuari River, Apure River system, in the upper Río Orinoco, but emphasized that the record should be confirmed. Lasso et al. (2004), in referring to this record added that the specimens probably belong to A. ginesi Lasso & Taphorn (= A. sardina ) or to a species not yet described. Lasso & Taphorn (2000) compared meristic data with specimens from the Río Ventuari to data taken from specimens of A. ginesi (= A. sardina ) and suggested that the former have more branched anal-fin rays and lateral-line scales than the latter (35-38 vs 29-36 and 73-76 vs 63-71 respectively). In two specimens (MZUSP 37268) from the Río Suripa, a tributary of Río Apure, Barinas, Venezuela, the number of anal-fin rays (36 and 37) and maxillary teeth (35 and 38) are outside the range of values for A. sardina (28-33 and 40-53 respectively) and differ from A. boehlkei by having more posterior dentary teeth (32 and 34 vs 20-33 in A. boehlkei ) and fewer small conical teeth in the outer row on the premaxilla (8 and 9 vs 9-12 in A. boehlkei ). This strongly suggests that the specimens from the Apure River system in Venezuela, tentatively identified as A. ginesi (= A. sardina ) and A. boehlkei probably belong to an undescribed species.

Figures

Fig. 9. Acestrocephalus boehlkei, MZUSP 12993, paratype, 85 mm SL, mature male, Río Punino, Río Napo drainage.

Fig. 10. Acestrocephalus maculosus, MZUSP 53974, holotype, 79 mm SL, immature female, córrego Água Parada, rio Tocantins 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.