Propimelodus araguayae, Rocha & de Oliveira & Rapp Py-Daniel, 2007

Rocha, Marcelo S., de Oliveira, Renildo R. & Rapp Py-Daniel, Lúcia H., 2007, A new species of Propimelodus Lundberg & Parisi, 2002 (Siluriformes: Pimelodidae) from rio Araguaia, Mato Grosso, Brazil, Neotropical Ichthyology 5 (3), pp. 279-284 : 280-284

Propimelodus araguayae , new species

Figs. 1, 2a

Holotype. INPA 26119, 127.1 mm SL, Brazil, Mato Grosso, Barra do Garças, rio Araguaia , 15°50’15”S 51°58’43”W, 15 Jun 2006, Humberto P. Rego.

Paratypes. INPA 26120 (8, 124.6- 131.9 mm SL) (2 cs, 121.5 mm SL), collected with the holotype . INPA 26121 (5, 114.1- 137 mm SL) (1 cs, 115 mm SL), Brazil, Mato Grosso, Barra do Garças, rio Araguaia , 15°50’15”S 51°58’43”W, 12 May 1992, Paulo C. Venere et al .

Diagnosis. Propimelodus araguayae can be distinguished from its congeners by: a conspicuous black dot on the dorsal-fin (vs. absent) ( Figs. 1-2); large eyes, 29.7-34.8% of head length and 62.7-74.7% of snout length (vs. 14.5-21.1% of head length and 31-44% of snout length in P. caesius and 9.5-19.7% of head length and 17-38% of snout length in P. eigenmanni ); anal-fin lobe present (vs. absent); tip of anterior medial process of basipterygium at the same level of the tip of the anterior lateral process (vs. anterior lateral process extending beyond the tip of the anterior medial process); premaxillary bone with three irregular rows of teeth (vs. 4-5 in P. caesius and 5-8 in P. eigenmanni ); total vertebrae count 43-44 (vs. 47-48 in P. caesius and 45-46 in P. eigenmanni ); gill rakers on first branchial arch 28-33 (vs. 20-23 in P. caesius and 19-20 in P. eigenmanni ).

Description. Morphometric data presented in Table 1. Maximum size 136 mm SL. Head profile convex from tip of the snout to posterior margin of orbit, then gently concave to nuchal plate. Dorsum profile almost horizontal from dorsal spine to adipose fin origin. From this point, profile falls in straight line and becomes slightly concave at end of adipose fin until caudal-fin base. Ventral profile gently inclined from mouth to pectoral-fin origin, convex along abdomen, straight from pelvic to anal-fin origin, then rising in a concave curve to caudal-fin base.

Dorsum of head covered with thin skin. Anterior nostril located immediately anterior to maxillary barbel base; anterior nostril tubular, dorsally oriented. Posterior nostril slightly closer to eye than to anterior nostril; posterior nostril rim with thin hyaline membrane elevated anteriorly and curving half way around aperture, incomplete posteriorly; aperture ovoid with its long axis oblique to longitudinal body axis. Distance between anterior nostrils smaller than distance between posterior nostrils. Anterior cranial fontanelle tapering anteriorly, opened from mesethmoid to frontals, terminating at or slightly anterior to posterior margin of eye. Posterior cranial fontanelle reduced to ovoid or circular foramen at center of supraoccipital. Supraoccipital process strong, wider at its base, reaching and interdigitating with anterior nuchal plate. Very large eye centered laterodorsally, with free orbital rim. Eye ovoid, horizontal diameter greater than interorbital width. Mouth ventral; corner of mouth posterior to maxillary barbel insertion; premaxillary bone with three irregular rows of conical and depressible teeth ( Fig. 3) exposed in ventral view. Upper lip expanded and visible ventrally. Fleshy rictal fold in pocket behind corner of mouth below insertion of maxillary barbel.

Cephalic lateral sensory canals thin; cutaneous canal branches dendritic and sometimes anastomosing on sides and top of head and on nuchal area. Lateral line canal complete, straight, terminating half way middle caudal-fin rays. Lateral line canal surrounded by superficial tubular ossicles, with few ventrally-oriented branches. Three anteriormost lateral line ossicles somewhat enlarged and associated with lateral edge of transverse processes of Weberian vertebrae. Dendritic cutaneous canal branches spreading across tympanic area.

Dentary with three rows of teeth near symphysis narrowing posteriorly to two rows. No teeth present on metapterygoid.

Three pairs of barbels. Maxillary barbel inserted close to anterior nostril and reaching beyond caudal-fin base.All mental barbels inserted at same level and approximately halfway distance from mandibular simphysis to gular fold apex. Inner mental barbel almost reaching insertion of pelvic fin. Tip of outer mental barbel reaching beyond insertion of anal fin.

Gill membranes free supported by 8-9 branchiostegal rays. Gill rakers well-ossified, sharp and slender: 28-33 (n=3).

Dorsal fin with eight dorsal-fin lepidotrichia: spinelet, spine, and six soft, branched rays. Dorsal spine straight, slender, without anterior dentations or anterior distal serrae, and bearing small terminal filament. Dorsal spine plus its own terminal filament about same size as first branched ray. Posterior margin of dorsal spine with sparse, small, sharp, and retrorse or erect dentations. Adipose fin long, inserted close to last dorsal-fin ray; its profile convex; its base length 35.8-39.0% of SL.

Pectoral fin with one spine and nine branched rays; first soft ray slightly longer than pectoral spine. Pectoral spine strong, sharp; posterior margin with numerous retrorse dentations regularly spaced; anterior margin with weak or no distal serrae but small antrorse dentations along middle third of spine. Posterior cleithral process triangular, short and sharply pointed. About 1/3 length of depressed pectoral spine.

Pelvic fin with six rays, first simple, second longest; inserted below penultimate dorsal-fin ray. Pelvic-fin margin gently convex nearly truncate. Extension of anterior medial process of basipterygium is approximately at same level as anterior lateral process.

Anal fin concave with nine branched and three simple rays; first and second branched rays more elongate with external tips expanded, forming well developed lobe. Last two anal-fin rays joined, articulating with single expanded pterygiophore.

Caudal fin deeply forked with slender, pointed lobes; without filament on tip of lobes; upper caudal-fin lobe usually longer. Fifteen branched caudal-fin rays. Total vertebrae 43- 44. First pair of ribs on sixth vertebra.

Urogenital papilla located in shallow depression immediately behind anus between pelvic fins about midway along length of inner fin rays. No apparent sex dimorphism. Distance from anus to anal-fin origin longer than caudal peduncle.

Color in alcohol. Body color light brownish to grey. White, unpigmented stripe ventral to lateral line. Nuchal plates covered with melanophores. Black spot on middle nuchal plate, extending onto base of dorsal-fin spinelet; adjacent nuchal plates also pigmented but not as dark. Dorsal fin with black coloration extending along four anteriormost branched rays, becoming more conspicuous on interradial membranes. Coloration extends up about halfway on first two rays, and fades gradually until fourth ray. Pectoral, adipose, anal, pelvic, and caudal fins hyaline.

Distribution. This species is known only from the middle rio Araguaia. These specimens were collected in Barra do Garças, Mato Grosso State, Brazil ( Fig. 4).

Etymology. The specific name (a noun in the genitive case) refers to the rio Araguaia (old spelling Araguaya).

Discussion. The presence of a robust palatine with a crest in the ectopterygoid joint, a synapomorphy for the genus Propimelodus , strongly suggests a close relationship of P. araguayae with P. eigenmanni and P. caesius ( Fig. 5), all showing the same condition of the ectopterygoid and endopterygoid bones. However, P araguayae is distinguished from its congeners by the features cited in the diagnosis, such as eye size, black dot on dorsal fin and anal-fin lobe ( Fig. 2).

The black dorsal-fin spot in P. araguayae shows a condition very different from that in P. eigenmanni , with a plain dorsal fin, and P. caesius , with a darkening on the distal tips of the first dorsal fin-rays ( Fig. 2).

The other two described Propimelodus species have an undeveloped anal fin lobe, thus differing from P. araguayae that has a well developed lobe, formed by the enlargement of the first two branched anal-fin rays. This developed condition is shared with Exallodontus aguanai . However, Exallodontus has a remarkable dentition, unique among Pimelodidae .

The number of total vertebrae is low in P. araguayae (43- 44) in comparison to the other described Propimelodus (45- 46 in P. eigenmanni and 47-48 in P. caesius ). According to Lundberg & Parisi (2002), low vertebral counts can be found in species of the “ Pimelodus -group” Pimelodus , Iheringichthys , Parapimelodus , and Duopalatinus peruanus .

Propimelodus araguayae also shares with its congeners an elongated pelvic symphysis developed between expanded membranous bone medial to the anterior limbs of the basipterygium. According to Parisi et al. (2006) these feature also occurs in Exallodontus , Pimelodus altissimus , Duopalatinus peruanus , Cheirocerus , and most members of the Calophysus -group ( Calophysus , Luciopimelodus , Pinirampus , Pimelodina ). However, in P. araguayae , the extension of the anterior medial process of the basipterygium is approximately at the same level as the anterior lateral process while in P. eigenmanni and P. caesius the anterior medial process surpasses the anterior lateral process ( Fig. 6).

Parisi et al. (2006) located additional feature shared by P. caesius , P. eigenmanni , and P. altissimus , that is the lateral margins of the posterior and middle nuchal plates, and the dorsal margin of the posterior cleithral process sharply jagged or serrated. However this condition was not found in Propimelodus araguayae .

The presence of nearly vertical neural spines of the posterior precaudal and anterior caudal vertebrae with distally expanded tips was also observed in Propimelodus araguayae , a condition found in Propimelodus eigenmanni , Exallodontus aguanai (Lundberg & Parisi, 2002) and Pimelodus altissimus .

This new species is presently known only from the middle part of the rio Araguaia, Mato Grosso State ( Fig. 4). Propimelodus eigenmanni and P. caesius are commonly found in white, sediment-rich waters and have never been found in the rio Araguaia.

Since its discovery in river channels, Propimelodus species was thought to be restricted to this peculiar environment and it has been usually captured with bottom trawl nets. However, the Araguaia species was captured by hook and line, at the banks of the rio Araguaia, near marginal macrophytes. This species is abundant in the middle course of the rio Araguaia, near Barra do Garças, the type locality, and it is used as food by local people.

Propimelodus eigenmanni is distributed in the Amazon drainage, between the lower rio Madeira and Belém ( Fig. 4), as well as in some Guyana rivers. Propimelodus caesius has the largest range of distribution of the genus, and has been collected from Peru to Belém in the Amazon mainstrem and the lower reaches of its principal tributaries.

It seems that P. araguayae might be endemic to the rio Araguaia. The intensive collecting effort of the Calhamazon Project (1993-1996) did not report this species in the large rivers of the Amazon. Recent expeditions on the middle to lower course of the rio Araguaia did not produce any Propimelodus araguayae , indicating a possible restricted distribution above the rio das Mortes mouth, in the middle course of Araguaia.