Plagioscion auratus (Castelnau 1855)

Lilian Casatti, 2005, Revision of the South American freshwater genus Plagioscion (Teleostei, Perciformes, Sciaenidae)., Zootaxa 1080, pp. 39-64 : 50-53

Plagioscion auratus (Castelnau 1855)

(Fig. 5)

Johnius auratus Castelnau 1855 : 12, pl. 4, fig. 2 (type-locality: Río Ucayali, Peru).

Sciaena aurata , Günther 1860: 287 ( new combination).

Corvina monacantha Cope 1866 : 402 (type-locality: Panamaribo, Suriname).

Plagioscion auratus , Jordan and Eigenmann 1889: 383 (revision).

Plagioscion monacanthus , Fowler 1919: 131.

Plagioscion monacantha , Travassos and Rego-Barros 1971: 61.

Material examined. Type specimens: MNHN 7622, holotype of Johnius auratus (198.0 mm SL), Río Ucayali, Amazon basin, Peru ; ANSP 11519, holotype of Corvina monacantha (166.2 mm SL), near Panamaribo, Suriname .

Non-types (54 specimens). Venezuela: Río Orinoco basin: AMNH 217675 (1) , CAS 50803 (1) , ANSP 149490 (1) , ANSP 53382 (1) , AMNH 8235 (2) , CAS 78510 [CM 7513 a] (1) , CAS 78509 [IU 13897] (1) , AMNH 73016 (2) ; Suriname: ANSP 11555 (1) ; French Guyana: MNHN 1981-542 (1) ; Brazil: Río Amazonas basin: USNM 52584 (1) , FMNH 59045 (1) , CAS 78518 [IU 5101] (1) , CAS 12128 [SU 22128] (3) , MCZ 10865 (1) , INPA 12896 (1) , INPA 605 (14, 1 C & S) , AMNH 3890 (2) , MCZ 10848 (3) , MCZ 10849 (2) , AMNH 3921 (1) , MPEG 3463 (3) , MZUSP 45943 (2) , MCZ 10850 (1) , MCZ 10855 (1) , MCZ 10853 (1) , INPA 10427 (1) , MCZ 10861 (1) , INPA 12934 (1) , CAS 147819 [SU 47819] (1) .

Diagnosis. A species of Plagioscion with the following combination of characters: anus distant from anal-fin origin (1.9-3.3 in HL); horizontal diameter of orbit 5.0-6.2 in HL; interorbital width wide (3.4-3.9 in HL); pectoral fin short, when depressed its tip not reaching vertical through anus; second anal-fin spine long (1.8-2.5 in HL); lower half of soft dorsal-fin covered with scales (usually 1-5 longitudinal series); second dorsal-fin with 32-38 (usually 34) soft rays; gill rakers 18-23. Plagioscion auratus also has the haemal spine of the first caudal vertebra expanded, with a posteroventral process that overlaps the anterodorsal portion of the first anal-fin pterygiophore, a condition unique to this species in the genus Plagioscion , albeit also present in the genera Haemulon , Polydactylus , Dendrophysa , Kathala , Larimus , and Pachypops .

Description. Morphometric and meristic data are presented in Table 2. Body elongated; maximum body depth at origin of dorsal fin. Dorsal profile of body convex. Ventral profile flattened from prepelvic region to anal-fin origin. Snout blunt in lateral view, short, as long as horizontal diameter of orbit. Mouth terminal, oblique in lateral view. Teeth conical, not visible externally; premaxilla with outer row of larger teeth and several inner rows of smaller teeth; dentary with 2 or 3 outer rows of smaller teeth and 1 inner row of larger teeth. Posteriormost tip of premaxillary bone reaching vertical through posterior margin of orbit. Eye round and small, horizontal diameter of orbit shorter than length of second anal-fin spine. Interorbital septum dorsally developed. Nostrils dorsolateral; anterior circular, posterior crescent-shaped, close to anterior margin of orbit. Laterosensory canal on head externally visible on lacrymal, suborbital, and preopercle. Preopercle margin smooth. Tip of opercle located posterior to vertical through pectoral-fin base. Posterior margin of postemporal bone covered with small ctenoid scales, appearing as bony flap above dorsal limit of gill slit. Gill rakers developed. Scales ctenoid, except for cycloid scales on snout, lachrymal, second to fourth infraorbitals, and preopercle. Lateral line extends to posterior margin of caudal fin, anterior one-third concave. Lateralline scales complex, formed of single basal larger scale covered by 4 or 5 smaller ones. Anal, pectoral, and pelvic fins with 1 or 2 rows of small ctenoid scales along their bases, and with few scales on basal half of membranes. Caudal fin almost completely covered by scales. Spinous dorsal-fin low, longest spine falls short of soft dorsal-fin origin when depressed. First dorsal-fin spine very small. Notch present between spinous and soft dorsal fins. Origin of soft dorsal-fin located along vertical through pectoral-fin tip. Anal fin truncate; first anal spine reduced and second long and strong, longer than half of longest soft ray. Caudal fin rhomboidal, with median rays longer in juveniles. Pectoral-fin falcate, falling short of vertical through tip of pelvic fin. Pelvic-fin origin located slightly behind vertical through pectoral-fin origin. First soft pelvic-fin ray longest, reaching anus. Gas bladder fusiform, with anterior pair of horn-shaped appendages.

Color in alcohol. Body dark-tan. Lighter individuals occasionally can be found in lots of dark specimens. Fins with brown chromatophores, resulting in a dark aspect. Axillary dark blotch present.

Distribution. Plagioscion auratus is known from the Río Orinoco and Río Amazonas basins, in Venezuela and Brazil, and the rivers of Suriname and French Guyana (Fig. 3). Travassos (1960) cited this species from the Río São Francisco, but I failed to locate specimens of this species among sciaenid samples examined from that drainage.

Remarks. Corvina monacantha was described by Cope (1866), based on one specimen from Suriname. Examination of the morphometrics, meristics (Table 2) and color pattern of the holotype of Corvina monacantha makes it clear that this species is a junior synonym of P. auratus .