Pimelodus britskii, Garavello & Shibatta, 2007

Garavello, Julio Cesar & Shibatta, Oscar Akio, 2007, A new species of the genus Pimelodus La Cépède, 1803 from the rio Iguaçu basin and a reappraisal of Pimelodus ortmanni Haseman, 1911 from the rio Paraná system, Brazil (Ostariophysi: Siluriformes: Pimelodidae), Neotropical Ichthyology 5 (3), pp. 285-292 : 287-290

Pimelodus britskii , new species

Figs. 4 and 5

Pimelodus ortmanni (part) Haseman, 1911: 379-380 (rio Iguaçu, Porto União da Vitória, current União da Vitória, Paraná State, Brazil); Severi & Cordeiro, 1994: 65 (figure); Azpelicueta, 1995:75 (reference); Nakatani et al., 2001: 277 (diagnosis; figure).

Pimelodus sp. : Garavello et al., 1997:76 (rio Iguaçu, Salto Segredo dam); Renesto et al., 2000: 810, fig. 2 (rio Iguaçu, Salto Caxias).

Holotype. FMNH 105098 , (ex FMNH 54241 and CM 2858 ) 297.0 mm SL, rio Iguaçu , Porto União da Vitória, (current União da Vitória), Paraná, Brazil, 27 Dec 1908, J. D. Haseman.

Paratypes. Brazil: Paraná: FMNH 105099 (ex FMNH 54241 and CM 2857 ), 1, 275.0 mm SL, rio Iguaçu, Porto União da Vitória ( União da Vitória ), 27 Dec 1908, J. D. Haseman; LISDEBE 1965, 10, 9.4- 21.3 mm SL, Candoi, rio Cavernoso , tributary of rio Iguaçu , upriver of Salto Santiago dam, near 10 km west from Candoi city, 20-26 Sep 1998, J. C. Garavello & A. S. Soares ; MZUEL 4725 , 3 , 273- 300 mm SL, rio Iguaçu, UHE Nei Braga, Salto Segredo , 13-14 Nov 2001, M. L. Orsi ; MZUSP 50037 , 37 , not measured, rio Iguaçu, downriver of Salto Osório dam at Quedas do Iguaçu , 30 Oct-6 Nov 1989, J. C. Garavello et al .; MZUSP 50038 , 91 (19, 86.9-221.3 mm SL), rio Iguaçu, downriver of Salto Osório dam at Quedas do Iguaçu , 30 Oct- 6 Nov 1989, J. C. Garavello et al .; MZUSP 50039 , 119 , not measured, rio Iguaçu, downriver of Salto Osório dam at Quedas do Iguaçu , 14-17 Jan 1990, J. C. Garavello et al .; MZUSP 50040 , 29 , not measured, rio Iguaçu, União da Vitória , 6 Mar 1979, Surhema collectors ; MZUSP 50042 , 15 (1, 94.9 mm SL), rio Iguaçu, downriver of Salto Santiago dam between Laranjeiras and Chopinzinho , 5-10 Nov 1990, J.C. Garavello et al .; MZUSP 50043 , 4 , not measured, rio Iguaçu , Porto Lupion, 1979/1980, Surhema collectors ; MZUSP 50046 , 1 , not measured, rio Iguaçu, downriver of Salto Osório dam at Quedas do Iguaçu , 13-15 Nov 1980, Surhema collectors . Santa Catarina: MZUSP 50044 , 11 (5, 186.6- 204.9 mm SL), rio Timbó, rio Iguaçu tributary at Colônia São Pedro , Porto União , 20-21 Nov 1986, J.C. Garavello et al .; MZUSP 50045 , 5 , not measured, rio Timbó, rio Iguaçu tributary at Colônia São Pedro , Porto União , 19-20 Nov 1986, J.C. Garavello et al .; MZUSP 50047 , 7 (1, 245.0 mm SL), rio Timbó, rio Iguaçu tributary at Colônia São Pedro, Porto União ; MZUSP 50041 , 17 , not measured, rio Timbó, tributary of rio Iguaçu at Colônia São Pedro , 18-19 Nov 1980, J.C. Garavello et al .

Diagnosis. Pimelodus britskii differs from its congeners, in its color pattern having circular dark brown blotches usually smaller than one orbital diameter regularly scattered along the trunk (vs. irregular series of dots in P. coprophagus, P. grosskopfi, P. paranaensis , P. navarroi, and P. pictus; small, densely placed oval or circular dots on anterior region of trunk, becoming inconspicuous or disappearing on caudal peduncle in P. absconditus , P. fur , P. heraldoi , and P. ortmanni , stripes along the body in P. albicans , P. albofasciatus, P. ornatus , and P. tetramerus ; uniform gray coloration or with very weak dark dots on anterolateral region in P. altissimus , P. argenteus , P. atrobrunneus , P. blochii , P. brevis, P. jivaro, P. microstoma, P. pohli, and P. punctatus; blotches larger than one orbital diameter in the trunk in P. maculatus , P. mysteriosus , and P. platicirris ). Pimelodus britskii also differs from P. ortmanni in having body depth at posterior cleithral process greater than head length (vs. depth always shorter than head length); lips not prominent (vs. fleshy and prominent lips circumscribing mouth opening); and maxillary barbel reaching or surpassing vertical drawn through median of adipose fin (vs. maxillary barbel reaching but not surpassing vertical drawn through median of adipose fin).

Description. Morphometric data presented in Table 1. Dorsal profile inclined from tip of snout to dorsal fin origin, slightly concave to almost straight between dorsal and adipose fin, concave at caudal peduncle region. Dorsal fin anterior to vertical through midline of body; predorsal length 2.3 to 2.6 (mean 2.4) times in SL. Body depth anterior to dorsal fin greater than its width at the posterior cleithral process. Head outline nearly trapezoidal in dorsal view, wedge-like in lateral view. Predorsal plate V-shaped, anterolaterally surpassing supraoccipital bone; predorsal plate and supraoccipital process conspicuously covered by skin. Orbit large, 1.1 times in interorbital distance; frontal fontanel origin between posterior nares not reaching vertical through posterior margin of orbit; mouth inferior, lower mandible shorter than superior; lips thin. Villiform teeth in premaxillary and dentary tooth plates; premaxillary tooth plates undivided at symphysis, semicircular margins, slightly curved posteriorly. Dentary tooth plate elongate, distally pointed, divided at symphysal region. Teeth absent in vomer and ectopterygoid bones; gill rakers long, slender. Barbels narrow, elongate; maxillary barbel reaching or surpassing vertical drawn through median of adipose fin, it may reach fork of caudal fin in juveniles; external mental barbel generally reaching pectoral fin, sometimes reaching pelvic-fin origin; ventral profile slightly convex from mouth to end of anal fin, concave at caudal peduncle. Body depth at posterior cleithral process greater than head length. Pectoral fin typically reaching vertical through base of fourth dorsal-fin ray, occasionally reaching only base of third dorsal-fin ray; pelvic fin reaching vertical through origin of adipose fin when depressed. Anal fin nearly triangular, slightly concave along distal margin; anal fin shorter than head length. Caudal fin bifurcated, upper lobe longer than lower. Cleithral process short, nearly triangular, not reaching vertical through origin of dorsal fin, occasionally reaching vertical through median predorsal plate. Unbranched dorsal-fin ray elongated, anterior margin smooth, posterior margin covered with hooks at 2/3 of distal region. Unbranched pectoral-fin ray elongated, aculeate, small hooks on anterior margin of its base; retrorse hooks on approximate one third of distal region of posterior margin. Dorsal fin rays II,6; pectoral fin I,9-10; pelvic fin i,5; anal fin iii, v, 7-10; caudal fin i,7,8,i. Gill-rakers 20-24 on first left branchial arch.

Color in alcohol. Dorsal region grayish, ventral region light brown; dark brown blotches, usually smaller than one orbital diameter, widely separated, arranged in three (rarely four) longitudinal series in trunk; dark brown dots in snout, opercle, infraorbital, parietal and supraoccipital regions. One series of small dark brown dots above and below lateral line, dorsal surface of body, in juveniles; series typically absent in adults. Eyes dark. One to three dark brown circular blotches on posterior cleithral process; dark brown dots on dorsal fin rays and membranes; pectoral, pelvic, anal, and adipose fins uni- formly grayish; dark brown dots rarely in adipose fin; dark dots on both lobes of caudal fin; brown pigment sometimes dotting only upper lobe.

Distribution. Distributed broadly throughout the rio Iguaçu basin ( Fig. 3 ).

Etymology. The name Pimelodus britskii is given in honor of the eminent ichthyologist Dr. Heraldo Antonio Britski, of Museu de Zoologia da Universidade de São Paulo, in recognition for his significant contributions to Neotropical systematic ichthyology.

Morphometric analysis. The size-free canonical variate analysis readily discriminated populations of P. ortmanni , P. britskii from rio Iguaçu and P. maculatus from the río de La Plata and rio Paraná basins ( Fig. 6 ), previously diagnosed on the basis of its color pattern. The eigenvalues and their loadings appear in Table 2. The first canonical axis (CAN1) readily separates all three species, while the second canonical axis (CAN2) distinguishes the specimens of P. britskii from the samples of P. ortmanni and P.maculatus , which have similar scores on CAN2. Pimelodus maculatus has a greater caudal peduncle depth, pectoral girdle width, interorbital and predorsal distance than does P. ortmanni . Pimelodus ortmanni has a larger distance between the bases of the anal and caudal fins, adipose fin length and distance from dorsal to adipose fin. The sample of P. britskii was discriminated from P. ortmanni and P. maculatus on CAN1 and CAN2. Pimelodus ortmanni was discriminated from P. britskii by a longer dorsal-fin base length and greater distance between the terminus of dorsal-fin and anal-fin origin; there are also differences in adipose-fin length. Pimelodus britskii has a larger distance between the orbit and opercular opening, predorsal distance and snout length (Table 2).

Figures

Fig. 4. Lateral view of Pimelodus britskii, FMNH 105098, holotype, 297.0 mm SL, rio Iguaçu, União da Vitória.

Fig. 5. Lateral view of Pimelodus britskii, MZUSP 50037, paratype262.0 mm SL, rio Iguaçu, downstream from Salto Osório dam at Quedas do Iguaçu.

Fig. 3. Geographical distribution of Pimelodus ortmanni and Pimelodus britskii from Rio Iguaçu. Each symbol may represent more than one sample.

Fig. 6. Scatter plot resulting from the size-free canonical variate analysis of P. britskii (squares), P. ortmanni (diamonds) and P. maculatus (triangles).