A New Species of Characidium Reinhardt (Characiformes, Crenuchidae) with a Distinctively Dimorphic Male
We herein describe Characidium satoi, new species, only known from its type locality at Rio Curral das Éguas, a small tributary of Rio Abaeté, in the Rio São Francisco basin, Brazil. It can be distinguished from its congeners by the following characteristics: area between the pelvic fin and the origin of anal fin moderate to strongly convex in lateral view; presence of irregular and discontinuous bars, forming dorsal blotches separated from ventral V-, W-, or diamond-shaped marks; and the first anal-fin radials inserted between the fifth and sixth caudal vertebrae. The juveniles and mature females of Characidium satoi, new species, have smooth fin rays, while mature males have hooks on pelvic and, in some specimens, pectoral and dorsal fins. Moreover, females and immature males have irregular bars on dorsum and fuzzy vertical bars on body; during the breeding season, males develop uniformly darker pigmentation on body and head, lacking any distinctive vertical bar on body. This seasonal color dimorphism is reported in the family Crenuchidae for the first time.
Landmarks on body (left) and head (right) of Characidium used for taking morphometric data: (1) tip of snout; (2d, v) posteriormost tip of dorsal or ventral caudal-fin lobe, respectively; (3) middle of vertical line that passes through the posterior edge of hypurals; (4) posterior tip of opercle bone; (5) origin of pectoral fin (=base of anterior pectoral-fin ray); (6) tip of the third unbranched pectoral-fin ray; (7) origin of dorsal fin; (7′) contralateral spot on belly to origin of dorsal fin, for the body depth at the origin of dorsal fin; (8) tip of the second dorsal-fin ray; (9) insertion of the dorsal fin; (10) origin of pelvic fin; (11) tip of the unbranched pelvic-fin ray; (12) anus; (13) origin of anal fin; (13′) contralateral spot on dorsum to origin of anal fin, for the body depth at the anal-fin origin; (14) tip of second anal-fin ray; (15) tip of longest anal-fin ray; (16) insertion of anal fin; (17) origin of adipose fin; (18) distal tip of adipose fin; (19 and 19′) origin of dorsal and ventral anterior procurrent caudal-fin ray, respectively; (20) anterior, soft margin of eye; (21) posterior, soft margin of eye; (22) ventral, soft margin of eye; (23) posterior tip of maxilla; (24) anterior rim of anterior naris; (25) anterior rim of posterior naris; (26) posterior prolongation of dermal fold that overlays the maxilla when mouth is closed; (27) lateral margin of frontal bone, at its greatest concavity. Continuous line indicates the body limits, and dotted line indicates bones only seen by transparence of skin; abbreviations are: op, opercle bone; sop, subopercle bone.
Characidium satoi, new species: (A) holotype, MZUSP 114614, 50.7 mm SL, female, in dorsal, lateral, and ventral views; (B) paratype, MZUSP 95289, 48.5 mm SL, dimorphic male in dorsal, lateral, and ventral views; (C) paratype, MZUSP 11464, 52.8 mm SL, female in dorsal and lateral views; (D) paratype, MZUSP 11464, 50.0 mm SL, female, in dorsal and lateral views, and (E) same as (D), live specimen. All specimens from Córrego Curral das Éguas, Três Marias, Minas Gerais (18°07′13″S 45°24′52″W).
Topographic map of the Rio São Francisco basin; only states within the drainage are indicated. The Upper São Francisco is highlighted, with indications for type locality of Characidium satoi (triangle), sites mentioned in text (circles), and major rivers. State acronyms are as follows: AL, Alagoas; BA, Bahia; DF, Distrito Federal; GO, Goiás; MG, Minas Gerais; SE, Sergipe; PE, Pernambuco.
The caudal peduncle of a cleared-and-stained specimen of Characidium satoi (MZUSP 95289, 44.6 mm SL), showing the relative position of anal-fin insertion in relation to the first caudal vertebrae (asterisk) and the anus (arrow).
Contributor Notes
Associate Editor: R. E. Reis