Steindachneridion punctatum (Miranda Ribeiro, 1918)

Garavello, Julio Cesar, 2005, Revision of genus Steindachneridion (Siluriformes: Pimelodidae), Neotropical Ichthyology 3 (4), pp. 607-623 : 616-617

Steindachneridion punctatum ( Miranda Ribeiro, 1918) Fig. 8

Steindachneria scripta var. punctata Miranda Ribeiro, 1918: 642 (text).

Steindachneridion punctata: Figueiredo & Costa Carvalho, 1999:692 (ref.).

Diagnosis. Steindachneridion punctatum differs from its congeners by the following combination of characters: supraoccipital process distant from anterior nuchal plate nearly one orbital diameter; premaxillary tooth plates large, united, medially grooved and curved distally; a single vomer dental plate oval, not grooved and distally circumscribed by premaxillary tooth plate in each side; 12 to14 gill rakers on first branchial arch; lips thin; maxillary barbel short, reaching or only slightly surpassing the opercular opening. Caudal peduncle depth high, 32.0 to 36.1% of head length; head depth shorter than head width (63.4 to 88.4%); and head width moderately large, 21.4 to 24.8% of SL; caudal fin slightly notched, dorsal and ventral lobes equal. Ground color of head and trunk light gray, abdomen yellowish with numerous small circular and semicircular dark brown blotches and dots irregularly scattered on head, trunk, rays and membrane fins.

Description. Morphometric data presented in Table 2; maximum body length 697 mm SL. Snout long and robust; snout tip roughly rounded in dorsal view; each pair of nostrils protruding on dorsal snout profile; anterior pair of more widely spaced apart than posterior pair. Head short and high in dorsal view, tip of snout nearly rounded in dorsal view and slightly depressed in lateral view; head depth shorter than its width 63.4 to 88.4%; head depth 15.1 to 21.7% of SL; head length 28.4 to 30.8% of SL. Dorsal profile of head almost straight from tip of snout to supraoccipital process; slightly depressed between from this point to anterior nuchal plate; supraoccipital process distant from the nuchal plate by nearly one orbital diameter long. Eyes dorsally placed and inserted in midway from snout tip and opercular opening; orbit moderate small, its diameter 8.6 to 11.7% of HL and 26.4 to 36.5% of interorbital distance.

Opercular opening large and with branchial membranes joining at narrow isthmus; eight branchiostegal rays reduced in size; 12 to14 gill rakers on first branchial arch. Lower region of head with arrow-like, shallow gular fold; deep grooves at lower jaw distal margin. Mouth large and terminal; mouth width 43.4 to 48.0% of HL; lower jaw shorter than upper jaw; thin lips; posterior postcleithral process short, reaching vertical line through distal supraoccipital process; all barbels narrow and depressed; maxillary barbel short, when adpressed reaching or only slightly surpassing the opercular opening; a pair of short mental and post-mental barbels on each side. Tooth plates of premaxillary and dentary provided with villiform teeth; premaxillary tooth plates large, united and grooved at middle, narrowing and curved inward distally; single vomer dental plate not grooved, almost elliptical in adults and juveniles, circumscribed by the premaxillary tooth plate; dentary tooth plate thin, single and distally sharp.

Body profile slightly convex from distal head to dorsal-fin origin; dorsal-fin base and posterior region almost straight; base of adipose fin slanted; dorsal profile of caudal peduncle slightly concave from end of adipose fin to caudal-fin origin. Predorsal length 41.3 to 44.1% of SL. Ventral profile of body straight inclined from tip of snout to end of opercular bone, slightly convex at middle abdominal region, slanted on pelvic and almost straight at anal-fin insertion; lower caudal peduncle profile slightly concave; cross section of caudal peduncle at vertical through posterior tip of anal fin approximately rounded. Dorsal-fin rays i,7(6); first two rays moderately spinous; dorsal-fin base inserted in the dorsal space between vertical through pectoral-fin terminus and anal-fin origin; dorsal fin locking mechanism present. Pectoral fin short and pectoral spine not pungent; fin tip reaching vertical through first dorsal-fin ray; pectoral-fin rays i,9(10), distal margin straight inclined and both margins of unbranched pectoral ray devoid of serrae. Pelvic-fin short; i,5 rays; tip of unbranched pelvic-fin ray not pungent; when adpressed surpassing the anus, but not reaching the anal-fin origin; posterior margin of pelvic-fin slightly rounded; Anal-fin rays i,8(9,10), posterior margin semicircular. Preanal distance 69.5 to 74.6% of SL. Caudal peduncle low its depth 9.8 to 11.1% of SL. Caudal fin slightly notched, with both lobes same sized, fin tip roughly rounded; 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 covered by thin skin, reaching vertical through distal opercular opening. Posterior postcleithral process short and entirely covered by skin.

Color in alcohol. Ground color of head, dorsum and lateral regions of body light gray and ventral region whitish; dorsal and lateral portions of head and trunk with small black and or dark brown circular or semicircular blotches; blotches shorter than one orbital diameter, irregularly scattered; lower region of head and abdomen yellowish; juveniles with lateral small dark brown dots on dorsal surface of body. Eyes dark. Dorsal, pectoral, pelvic, anal and adipose fins uniformly dark gray, small dark brown dotted on rays and membranes; adipose fin with several black or dark brown dots; caudal fin with dark spots on base of each lobe, but distally uniformly dark gray.

Distribution. Known from the upper rio Paraná, and rio Uruguay basin, Brazil ( Fig. 1 ).

Material examined. Rio Grande do Sul State : Holotype, MNRJ 1167, 330 mm SL, rio Uruguay, Itaqui; E. Garbe, 1914. MCP 12634, 1, 437 mm SL and MCP 12635, 1, 363 mm SL, rio Pelotas , Esmeralda, on the road Garibaldi to Pinhal da Serra , 11 Dec 1988. MCP 12628, 1, 428 mm SL, rio Uruguay, Barracão at confluence of Pelotas and Canoas rivers, 10-11 Dec 1988. MCP 12847, 1, 245 mm SL, Campos Novos , rio Canoas , on the road Abdon Batista to A. Garibaldi, 22-23 Jan 1989. São Paulo State: MZUSP 23093 , 2 , 330 and 414 mm SL, ilha Solteira , rio Paraná , Sep 1965. MZUSP 87985 , 1, 632 mm SL, Jaguara , rio Grande , Cachoeira Mata-Doutor, downstream of Jaguara hydroeletric power dam, 24-30 Jun 1988.

Figures

Fig. 8. Lateral and dorsal views of S. punctatum. MZUSP 87985, 632 mm SL, Jaguara, rio Grande, Cachoeira Mata-Doutor, downstream of Jaguara hydroeletric power dam, São Paulo, Brazil.

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