Steindachneridion doceanum (Eigenmann & Eigenmann, 1889)

Garavello, Julio Cesar, 2005, Revision of genus Steindachneridion (Siluriformes: Pimelodidae), Neotropical Ichthyology 3 (4), pp. 607-623 : 613-615

Steindachneridion doceanum

(Eigenmann & Eigenmann, 1889)

Figs. 5-6

Steindachneria doceana Eigenmann & Eigenmann, 1889: 30 , syntypes MCZ 23792, 23793 and 23794 (examined). Type locality: rio Doce , Brazil; Eigenmann & Eigenmann, 1890: 204 (types); Eigenmann & Eigenmann, 1891: 31 (ref.); Eigenmann, 1910: 391 (ref.); Ribeiro, 1911: 299 (458) (ref.); Van der Stigchel, 1947: 67 (Rio de Janeiro).

Steindachneridion doceana: Gosline, 1945: 51 (ref.); Fowler, 1951: 603 (ref.); Burgess, 1989: 282; Lundberg et al., 1991: 842; Oliveira & Moraes Junior, 1997: 3; Lundberg & Littmann in Reis et al., 2003: 443.

Diagnosis. Steindachneridion doceanum differ from the remaining species of genus by the following combination of characters: supraoccipital bone process almost in contact with anterior nuchal plate; premaxillary tooth plates large, grooved medially and distally sharp; vomerine tooth plate oval, deeply grooved medially or divided in juvenile specimens; 18 to 20 gill rakers on first branchial arch; pectoral, adipose and pelvic fins large; pelvic fin long, concealing the anus. Lips protruded; maxillary barbel short, reaching to base of unbranched pectoral-fin ray. Color pattern marbled, combining dark brown large bowed lines with ground yellowish lines in a light brown ground color. Caudal peduncle low, its depth 26.1 to 30.9% of HL; head depth low, comprising 55.8 to 79.6% of head width; head width small, 21.9 to 23.2% of SL.

Description. Morphometric data presented in Table 1; maximum body length 420 mm SL. Snout slender; snout tip almost elliptical in dorsal view; snout length 12.9 to 13.1% of SL; anterior pair of nostrils inserted more widely spaced apart than posterior pair; each pair of nostrils protruding on dorsal snout profile. Head long in dorsal view and depressed in lateral view; head low its depth 55.8 to 79.6% of head width; and 21.9 to 23.2% of SL; head length 28.3 to 29.3% of SL. Dorsal profile of head increasing in an almost straight line from tip of snout to nuchal plate; slightly elevated at the orbital region; supraoccipital process almost in contact with anterior nuchal plate. Eyes dorsally placed midway between snout tip and opercular opening; orbit large, orbital diameter 10.3 to 11.7% of HL and 30.4 to 35% of interorbital distance.

Opercular opening large and strongly curved; branchial membranes joining before forming a narrow isthmus; eight branchiostegal rays progressively reduced in size; 18-20 gillrakers on first branchial arch. Lower region of head with an arrow like and shallow gular fold; deep grooves at posterior margin of lower jaw. Mouth terminal; mouth width 49.1 to 52.0% of HL; lower jaw shorter than upper jaw; lips thick; posterior postcleithral process short, reaching vertical line passing through terminus of supraoccipital process. All barbels, narrow and depressed; maxillary barbel short, reaching or only slightly surpassing the median region of pectoral fin when adpressed; a pair of short mental and post-mental barbels on each side. Tooth plates of premaxillary and dentary ramus with villiform teeth; premaxillary tooth plate slender, with median groove and abruptly narrowing and curved inward distally; single vomerine tooth plate grooved medially in adults; vomerine tooth plate divided into two small elliptical plates almost in contact at median region of vomer in juveniles; both vomerine tooth plates circumscribed by premaxillary tooth plate; and single elongate and distally sharp dentary tooth plate.

Body profile slight convex between posterior nuchal plate and origin of adipose fin; dorsal-fin base slanted; region between dorsal and adipose-fin origin slightly concave; dorsal profile of caudal peduncle deeply concave from end of adipose fin to origin of caudal-fin. Predorsal length long, 38 to 40% of SL. Ventral profile of body almost straight and slanted from tip of snout to end of opercular bone, slightly convex at middle inferior head and abdominal region, flat on pelvic-fin insertion; base of anal fin straight and posteriorly slanted; preanal distance 69.3 to 71.6% of SL; lower caudal peduncle profile slightly concave; adipose fin large and convex. Caudal peduncle at vertical through posterior tip of anal fin approximately rounded in crossed section. Dorsal-fin rays i,7(6); dorsal-fin base inserted in dorsal space between vertical through pectoral-fin terminus and anal-fin origin; dorsal fin locking mechanism present. Pectoral fin long, tip of fin surpassing vertical through dorsal-fin insertion; rays i,9(10); distal margin rounded; pectoral spine short and not pungent, both margins devoid of serrae. Pelvic-fin long, its tip not pungent and reaching anal-fin insertion; pelvic-fin rays i,5; its distal margin slightly rounded; pelvic-fin when adpressed concealing anus and reaching anal-fin origin. Anal-fin rays i,8(9), its distal margin rounded. Caudal peduncle low, its depth 7.7 to 9% of SL. Caudal fin slightly notched, with dorsal lobe slightly larger than ventral, fin tip slightly pointed; principal caudal-fin rays, i,15,i.

Body and head except orbital region covered with thick skin. Ventral surfaces of pectoral and pelvic girdle entirely covered by skin; supraoccipital process short and covered by thin skin, very near the anterior nuchal plate. Posterior postcleithral process short and entirely covered by skin.

Color in alcohol. Ground color of head, dorsum and lateral region of body light gray and ventral region yellowish; dorsal and lateral portions of head and trunk with maze dark brown lines forming like a marbled color pattern, combined with light gray ground color extending onto all fins; lower region of head and abdomen yellowish. Eyes dark. Dorsal, pectoral, pelvic, anal and adipose fins uniformly light gray and with lines forming marbled pattern on rays and membranes; adipose fin with several dark brown lines; caudal fin with dark lines on base of each lobe, gray distally.

Distribution. Known from the rio Doce basin, Brazil ( Fig 1 ).

Material examined. Espírito Santo State: MCZ 23794 (syntype), 307 mm SL, rio Doce between Linhares and Aimorés, 1865 . Minas Gerais State: MZUSP 87988 , 1, 420 mm SL, Ponte Nova, rio Piranga, tributary of rio Doce , 28 May to 5 June 1995 . MZUSP 87989 , 1, 310 mm SL , Santa Cruz do Escalvado, rio Doce , 24 Nov to 4 Dec 1995 .

Figures

Fig. 5. Lateral and dorsal views of S. doceanum. MZUSP 87988, 420 mm SL, Ponte Nova, rio Piranga, tributary of rio Doce, Minas Gerais, Brazil.

Fig. 6. Lateral view of S. doceanum, syntype. MCZ 23794, 307 mm SL, rio Doce between Linhares andAimorés, Espírito Santo, Brazil.

Fig. 1. Southeastern South America with the geographical distribution of Steindachneridion species. Each symbol may represent more than one sample.