Plagioscion squamosissimus (Heckel 1840)

Lilian Casatti, 2005, Revision of the South American freshwater genus Plagioscion (Teleostei, Perciformes, Sciaenidae)., Zootaxa 1080, pp. 39-64 : 42-49

Plagioscion squamosissimus (Heckel 1840)

(Fig. 2)

Sciaena squamosissima Heckel 1840 : 438, pl. 30, figs. 26-28 (type-locality: Río Negro and Río Branco, Brazil).

Johnius crouvina Castelnau 1855 : 11, pl. 5, fig. 1 (type-locality: Río Araguaia and Río Crixas, Brazil).

Johnius amazonicus Castelnau 1855 : 12, pl. 4, fig. 1 (type-locality: Río Amazonas, Brazil).

Sciaena amazonica , Günther 1860: 284 ( new combination).

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

Pseudosciaena surinamensis Bleeker 1873 : 458, pl. 21, side figure (type-locality: Suriname).

Plagioscion squamosissimus , Jordan and Eigenmann 1889: 381 (revision).

Plagioscion auratus iquitensis Nakashima 1941 : 67 (type-locality: Iquitos, Peru).

Plagioscion squamosissimus iquitensis Nakashima 1941 : 68 (type-locality: Iquitos, Peru).

Plagioscion casattii Aguilera & Aguilera 2000 : 61, fig. 1 (type-locality: Río Orinoco, Venezuela).

Material examined. Type specimens: NMW 92124, holotype of Sciaena squamosissima (485.0 mm SL, dry), Río Negro and Río Branco ; MNHN 7504, holotype of Johnius amazonicus (197 mm SL), Río Amazonas ; MNHN 7503, holotype of Johnius crouvina (370 mm SL), Río Crixas, tributary to Río Araguay, Brazil ; RMNH 5995, holotype of Pseudosciaena surinamensis (88.2 mm SL), Suriname ; DZSJRP 5482 [ MBUCV -V - 29491], two paratypes of Plagioscion casattii (255.0-258.0 mm SL), Río Orinoco, obtained in Cuidad Bolívar market, State of Bolívar, Venezuela .

Non-types (335 specimens). Venezuela: Río Orinoco basin: USNM 233372 (2) , USNM 233374 (2) , AMNH 217658 (2) , MCZ 59662 (1) , USNM 233381 (2) , CAS 50802 (2) , USNM 233320 (2) , AMNH 217714 (1) , ANSP 149502 (1) , USNM 233317 (2) , USNM 260103 (1) , ANSP 165490 (1) , USNM 258256 (1) , ANSP 165363 (2) , ANSP 160182 (2) , ANSP 160207 (1) , ANSP 166569 (2) , ANSP 166607 (2) , ANSP 160897 (1) , ANSP 160330 (2) , ANSP 163024 (2) , ANSP 160897 (1) , ANSP 160181 (1) ; Guyana: Essequibo River basin: FMNH 59291 (1) , AMNH 72895 (1) , AMNH 220499 (1) ; Suriname: RMNH 18127 (2) , RMNH 16258 (2) , USNM 226087 (2) , USNM 226088 (1) , AMNH 54739 (2) , USNM 226085 (1) , MNHN A4098 (1) ; Colombia: Río Metica basin: ANSP 139819 (1) , ANSP 135570 (2) , ANSP 140329 (1) , ANSP 135568 (2) , ANSP 135571 (2) , ANSP 139820 (2) ; Ecuador: Río Napo basin: FMNH 101965 (2) , FMNH 101966 (2) ; Peru: Río Napo basin: INPA 12893 (1) ; Río Marañon basin: USNM 167716 (1) , CAS 78515 [IU 16149] (2) , ANSP 139091 (2) , ANSP 139092 (1) , ANSP 139098 (1) , CAS 78514 [IU 16150] (1) , ANSP 139094 (1) , INPA 12900 (1) , INPA 12894 (1) , INPA 12985 (1) , MZUSP 15314 (1) , INPA 12993 (1) , ANSP 139090 (1) , CAS 78511 [16147], (2) , CAS 78516 [IU 16146] (1) , ANSP 96044 (3) ; Bolivia: Río Mamoré- Guaporé basin: FMNH 107240 (1) , MNHN 1988-1960 (3) , MNHN 1988-1063 (1) , MNHN 1988-1961 (3) , CAS 17251 (2) , USNM 222887 (2) , USNM 305798 (1) , AMNH 40165 (1) , MNHN 1988-1962 (1) , USNM 305796 (1) ; Brazil: Río Amazonas basin: MZUSP 34080 (2) , INPA 5020 (1) , INPA 3162 (3) , INPA 3156 (1) , INPA 3162 (2) , MZUSP 34128 (1) , ANSP 149942 (1) , INPA 3161 (2) , INPA 3163 (1) , MZUSP 34127 (1) , INPA 12937 (2) , MCZ 10870 (1) , MCZ 10871 (1) , INPA 6543 (2) , INPA 12933 (1) , INPA 12939 (1) , MZUSP 34121 (1) , INPA 12369 (3) , INPA 12925 (3) , MZUSP 34122 (3) , MZUSP 34078 (2) , MZUSP 48971 (2) , MZUSP 6605 (2) , CAS 78513 [IU 16148] (1) , MZUSP 5865 (2) , MZUSP 6753 (2) , MZUSP 27596 (2) , MCZ 10863 (1) , MZUSP 27615 (1) , MZUSP 14382 (1) , MZUSP 14378 (2) , MZUSP 14682 (2) , MZUSP 36106 (1) , MZUSP 36113 (1) , MZUSP 36111 (1) , MZUSP 2511 (1) , INPA 8951 (1) , INPA 602 (2) , MZUSP 45942 (3) , USNM 316882 (2) , INPA 12920 (2) , INPA 12920 (2) , INPA 10463 (1) , INPA 2728 (2) , INPA 11991 (2) , INPA 5528 (1) , INPA 12919 (5) , INPA 2729 (1) , MZUSP 5988 (1) , INPA 8178 (2) , INPA 8276 (3) , MZUSP 14690 (1) , MZUSP 14379 (1) , MZUSP 49617 (1) , USNM 94661 (1) , MZUSP 7028 (3) , MZUSP 14689 (2) , MZUSP 14683 (1) , MNHN 1998-0276 (8) , MZUSP 45948 (2) , MCZ 10867 (1) , MCZ 10866 (1) , INPA 12910 (1) , INPA 12905 (2) , INPA 12898 (2) , INPA 12915 (2) , INPA 12914 (2) , INPA 12907 (2) , MZUSP 47443 (3) , MZUSP 9442 (1) , MZUSP 45941 (1) , MZUSP 34085 (3) , MZUSP 12120 (2) , MZUSP 45939 (2) , CAS 78512 (1) , MZUSP 5672 (2) , MZUSP 5693 (2) , MZUSP 34131 (1) , MZUSP 9585 (1) , CAS 32053 (2) , CAS 32052 (1) , CAS 156733 [SU 56733] (1) , MZUSP 14685 (1) , USNM 163774 (1) , INPA 7136 (2) , MZUSP 3611 (2) , MCZ 10856 (1) , MCZ 10852 (1) , MCZ 4576 (2) , MCZ 36204 (1) , MCZ 10847 (2) , MCZ 10846 (1) , MZUSP 14384 (1) , MNRJ 2141 (6) , MZUSP 51080 (2) , MZUSP 14375 (2) , MZUSP 51083 (1) , MZUSP 51081 (2) , MZUSP 51079 (1) , MZUSP 51082 (1) , MZUSP 34132 (1) , MZUSP 36882 (2) , MZUSP 35994 (1) , RMNH 16257 (1) , CAS 148677 (2) , INPA 12066 (1) , INPA 12927 (1) , MCZ 10851 (1) , MCZ 46860 (1) , MZUSP 50535 (1) , MZUSP 53016 (1) , MZUSP 50133 (2) , INPA 10452 (1) , INPA 11990 (1) , INPA 10458 (1) , MZUSP 34089 (2) , MZUSP 34125 (2) , MZUSP 34079 (2) , MZUSP 34081 (1) , INPA 10447 (2) , MZUSP 34082 (1) , INPA 10459 (1) , MZUSP 53720 (2) , MZUSP 53719 (1) , MZUSP 14684 (2) , MNRJ 12737 (1) , MNRJ 13239 (3) , MNRJ 12610 (3) , MNRJ 12906 (1) , MZUSP 40398 (1) , MZUSP 40575 (1) , MZUSP 40767 (1) , MZUSP 40904 (2) , MZUSP 40861 (1) ; Río São Francisco basin: MNRJ 15328 (2) ; Río Paraná basin: MZUSP 40049 (1) , MZUSP 21654 (2) , MZUSP 21145 (3) , LIRP 1148 (2) .

Additional material. Río Trombetas basin: MZUSP 45945 (1) , MZUSP 34130 (1) , MZUSP 45944 (6) , MZUSP 14681 (2) , MZUSP 45946 (1) ; Río Tapajós basin: MZUSP 34131 (1) ; Río Xingu basin: MZUSP 45947 (6) , MPEG 1667 (1) .

Diagnosis. A species of Plagioscion with the following combination of characters: anus close to anal-fin origin (anus to anal-fin length 3.4-5.6 in HL); horizontal diameter of orbit 3.8-5.4 in HL; interorbital width narrow (2.8-4.8 in HL); pectoral fin short (3.8-4.7 in SL); second anal-fin spine short (mean 3.9 in HL); lower half of soft dorsal-fin covered with scales (usually 1-5 longitudinal series); large conical teeth in the inner series of premaxilla.

Description. Morphometric and meristic data are presented in Table 1. Body elongate; maximum body depth at origin of dorsal fin. Dorsal profile convex. Ventral profile flattened from prepelvic region to anal-fin origin. Snout blunt in lateral view, short, and as long as horizontal diameter of orbit. Mouth terminal, oblique in lateral view. Teeth conical, visible externally in many specimens; 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. Orbit lateral; eye round, its horizontal diameter usually as long as second anal-fin spine. Interorbital septum dorsally developed. Nostrils positioned dorsolaterally, close to anterior margin of orbit, their shape circular anteriorly and crescentic posteriorly. 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, and appearing as bony flap above dorsal limit of gill slit. Gill rakers well developed. Scales ctenoid, except for cycloid scales on snout, lacrymal, second to fourth infraorbitals, and preopercle. Lateral line extending to posterior margin of caudal fin, the anterior 1/3 concave. Lateral-line scales complex, formed of a single basal larger scale covered by 4 or 5 smaller scales. Anal, pectoral, and pelvic fins with 1 or 2 rows of small ctenoid scales along their bases, and with few scales on basal one-half of membranes. Caudal fin almost completely covered by scales. Spinous dorsal-fin low, the longest spine, when depressed, falling short of origin of soft-dorsal fin. 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 anal spine short and thin, length of the latter longer than horizontal diameter of orbit. Caudal fin rhomboidal, with median rays longer in juveniles. Pectoral fin falcate, with tip of fin falling short of vertical through tip of pelvic fin. Pelvicfin origin situated slightly behind vertical through pectoral-fin origin. First soft pelvic-fin ray longest, but falling short of anus. Gas bladder fusiform, with anterior pair of hornshaped appendages.

Color in alcohol. Head and dorsal portion of trunk yellowish-tan, lighter and silvery ventrally. On very rare occasions individuals can be darker. Opercle with irregular concentration of dark chromatophores. Fins hyaline; dorsal fin membrane with irregularly distributed brown chromatophores. Axillary dark blotch present.

Distribution. Plagioscion squamosissimus was originally limited to the Río Orinoco and Río Amazonas basins and rivers of the Guianas. Recently it has been introduced into the Paraná-Paraguay-Uruguay River system, the Río São Francisco basin and reservoirs of northeastern Brazil (Agostinho and Júlio Jr., 1999, Sato and Godinho, 1999) (Fig. 3).

Remarks. Plagioscion squamosissimus was described by Heckel (1840), based on specimens collected by Natterer in the Río Negro and Río Branco, Amazon basin, Brazil. Although the synonymy of Johnius amazonicus , J. crouvina and P. squamosissimus iquitensis dates from earlier authors, synonymization of Pseudosciaena surinamensis with P. squamosissimus is proposed for the first time in the present study. The holotype of Pseudosciaena surinamensis is a member of the group within Plagioscion in which the anus is separated from the anal-fin origin by a short distance (3.8 times in HL), which also includes P. squamosissimus and P. ternetzi . The holotype of Pseudosciaena surinamensis differs from Plagioscion ternetzi in having 31 dorsal-fin soft rays (vs. 34-37, usually 35). By contrast, characters for the holotype of Pseudosciaena surinamensis fall within the range of characters for Plagioscion squamosissimus , most notably the interorbital width and length of the second anal-fin spine (Fig. 3), which are the species’ two most diagnostic features. For these reasons Pseudosciaena surinamensis is herein considered a junior synonym of P. squamosissimus .

None of the type specimens of Plagioscion auratus iquitensis Nakashima were available for examination. However, some features in the original description (body dark tan, orbital diameter 4.64 in HL, second anal-fin spine length 3.25 in HL, interorbital width equal to orbital diameter) suggest that this species could be assigned either to P. auratus or to P. squamosissimus . The body color of P. auratus iquitensis resembles P. auratus , whereas orbital diameter, second anal-fin spine length, and interorbital width are more comparable to those found in P. squamosissimus . The majority of specimens of P. auratus are dark tan, but occasional individuals of P. squamosissimus can be unusually dark, and may approach the condition typical of P. auratus . The diameter of the orbit is 5.0-6.2 in HL in P. auratus and 3.8-5.4 in P. squamosissimus ; thus, the value of 4.64 times in HL in P. auratus iquitensis falls within the range of values for P. squamossimus . The second anal-fin spine length is 1.8-2.5 in HL in P. auratus and 2.6-6.0 in P. squamosissimus ; thus, the 3.25 times in HL reported for P. auratus iquitensis again falls within the range in P. squamossimus . Finally, the interorbital width is 3.4-3.9 in HL in P. auratus and 2.8-4.8 in P. squamosissimus ; thus, the value of 4.64 times in HL for P. auratus iquitensis again falls within the range of P. squamosissimus . Based on the above, Plagioscion auratus iquitensis is considered a junior synonym of P. squamosissimus . The second taxon described by Nakashima (1941) from Peru, P. squamosissimus iquitensis has features that completely overlap those of P. squamosissimus (body silvery, orbital diameter 4.0 in HL, second anal-fin spine length short, orbital diameter 1.16 in interorbital width [= interorbital width 3.8 in HL]), and is also considered a synonym of P. squamosissimus .

Plagioscion casattii was recently described (Aguilera & Aguilera, 2000) based on measurements taken on fresh specimens from the Río Orinoco basin. The authors pointed out the following differences between this nominal species and P. squamosissimus : lower number of gill rakers 15-18 (versus 20-25 in P. squamosissimus ), second anal spine length 4.0-6.3 in HL (versus 3.9 in P. squamosissimus ), interorbital width 4.8-5.3 times in HL (versus 4.3 in P. squamosissimus ), and tip of pelvic fin not reaching anus, with a mean distance that goes 6.5-10.0 times in SL (versus 3.2 in P. squamosissimus ). However, these supposed differences could not be confirmed by me from examination of two preserved paratypes of P. casattii (DZSJRP 5482, previously MBUCV-V-29491). Comparing paratypes of Plagioscion casattii with a sample of 94 specimens of P. squamosissimus (Table 1), I observed that the former have 19 gill rakers (versus 18-26 in P. squamosissimus ), second anal spine length 3.4-4.3 in HL (versus 2.6-6.0 in P. squamosissimus ), interorbital width 4.2-4.6 times in HL (versus 2.8-4.8 in P. squamosissimus ), and tip of pelvic fin not reaching anus by a distance that fits 9.1 times in SL (versus tip of pelvic fin not reaching anus by a distance that fits 6.0-24.8 times in SL in P. squamosissimus ). In view of the complete, or nearly complete, overlap of these values with P. squamosissimus , P. casattii is herein considered a junior synonym of P. squamosissimus .

The second anal-fin spine length in HL reveals differences among Plagioscion species; however, this proportional value is highly variable in P. squamosissimus , and the ranges overlap those seen in almost all remaining congeners (Fig. 3). The high variability in many morphometric features of P. squamosissimus (see Table 1) has almost certainly been an important factor in the recognition of species that are here considered synonyms (see Synonymy). Probably the main factor contributing to this variation is the broad geographic distribution of P. squamosissimus . Similar situations have been documented for other South American freshwater species with broad continental occurrences, such as Hoplias malabaricus (Oyakawa, 2003) and Rhamdia quelen (Silfvergrip, 1996).

Several lots of specimens listed as "additional material" in the list of non-types, from the Río Trombetas, Tapajós, and Xingu, show two characters (i.e., horizontal diameter of orbit; number of gill rakers) that differ somewhat from other specimens identified as P. squamosissimus . These specimen lots consequently are segregated from other lots in the list. Orbital diameter is 3.4-4.0 in HL in these specimens and 3.8-5.4 times in P. squamosissimus (U=83.0, p<0.0001]), and gill rakers number 15-18 in these specimens and 18-26 in P. squamosissimus (U=33.5, p<0.0001). Despite their statistical significance, overall there is overlap in these two characters among specimens from throughout the overall geographic range of P. squamosissimus , and there appear to be no other morphological differences that serve to distinguish specimens from these three drainages from specimens elsewhere. Although it was originally intended to describe these populations as a new species, I have now adopted a more conservative approach, and these specimens are tentatively referred to P. squamosissimus until such time as new and more sophisticated diagnostic techniques become available.