Prochilodus lacustris Steindachner 1907

Prochilodus lacustris Steindachner, 1907

Prochilodus lacustris Steindachner, 1907:152 (page 1 of separate) [type locality: See von Parnagua unde der nahegelegenen, Lagoa da Missão; Lagoas bei Sa. Filomena und am Rio Medonho einem Nebenflusse des Parnahyba (= Brazil, Piauí, Lagoa de Parnaguá, Lagoa da Missão, Santa Filomena and Rio Medonho, tributary to Rio Parnaíba), restricted herein to Brazil, Piauí, Lago de Parnaguá, Rio Gurguéia system].—Eigenmann, 1910:424 [in listing of South American fishes].—Fowler, 1950:220 [literature compilation]; 1975: 359 [literature compilation; common name].—Mago-Leccia, 1972:47 [use of caudal-fin pigmentation to discriminate groups of species].—Nomura, 1984: 54 [Brazil, common name].—Petrere, 1989:8 [economic importance].

Prochilodus argenteus [not of Agassiz, 1829].—Steindachner, 1915:21 [in part, incorrect synonymy of P. lacustris into P. argenteus].—Géry, 1977:222 [in part; not P. lacustris as synonym of P. argenteus].—Nomura, 1984:54 [Brazil, common name].

Prochilodus nigricans [not of Agassiz, 1829].—Nomura, 1984:54 [Brazil, common name].

DIAGNOSIS.—The pattern of dark, irregular, wavy, bar-like patterns on the caudal-fin lobes in Prochilodus lacustris discriminates that species from P. argenteus, P. britskii, P. costatus, P. hartii, P. lineatus, P. magdalenae, P. reticulatus, and P. vimboides, which have hyaline caudal fins. Within the group of five Prochilodus species with dark, irregular caudal-fin bars, P. lacustris differs from P. mariae in the number of scales along the lateral line (46 to 51, 47 most frequent with 51 in 2 of the 50 specimens examined for this feature, versus 52 to 64, 52 in only 1 of the 77 specimens examined for this feature, respectively), the number of scales along the middorsal series between the posterior of the dorsal-fin base and the adipose-fin origin (14 to 18, 16 most frequent, versus 17 to 23, 18 and 19 most frequent, respectively), and the number of dark, wavy, horizontal stripes ventral of the lateral line (6 or 7 versus 7 to 10, respectively); from P. brevis in the number of horizontal rows of scales between the pelvic-fin insertion and the lateral line (8 to 11, with 9 most frequent and 8 infrequent, versus 6 to 8, with 7 most frequent and 8 infrequent, respectively; Figure 36), the number of scales along the lateral line (46 to 51, 47 most frequent and 46 in only 17% of examined specimens, versus 41 to 48, 43 most frequent and 46 to 48 infrequent, respectively; Figure 37), and the number of vertebrae (41 to 43, with 42 most frequent and 41 in only 1 of 13 specimens examined for this feature, versus 40 to 42, with 42 and 41 most frequent and 42 in only 2 of 30 specimens examined for this feature, respectively; Figure 38); from P. rubrotaeniatus in the form of the scales (with only radial subdivisions versus having complex pattern of variable subdivisions), the number of horizontal rows of scales between pelvic-fin insertion and lateral line (8 to 11, 9 most frequent and 8 in only 8 of 51 specimens, versus 6 to 8, 6 most frequent and 8 in only 2 of 36 specimens, respectively); from P. nigricans in the form of the scales (with only radial subdivisions versus having complex pattern of variable subdivisions), the number of scales along the lateral line (46 to 51, 47 most frequent, versus 44 to 51, 49 most frequent, respectively), the number of horizontal rows of scales between the pelvic-fin insertion and the lateral line (8 to 11, 9 most frequent, versus 7 to 9, 8 most frequent, respectively), the number of median predorsal scales (15 to 22, 16 most frequent, versus 13 to 20, 17 most frequent, respectively), and the number of vertebrae (41 to 43, 42 most frequent, versus 40 to 45, 43 most frequent).

DESCRIPTION.—Morphometric and meristic data for Prochilodus lacustris presented in Table 10. Body comparatively high, transversely compressed. Greatest body depth at dorsal-fin origin. Dorsal profile of head gently concave. Predorsal profile of body convex. Body profile posteroventrally inclined along dorsal-fin base, straight from posterior of dorsal-fin base to adipose-fin origin, and concave along caudal peduncle. Predorsal portion of body with moderately developed median ridge. Postdorsal region of body transversely obtusely rounded. Ventral profile of body convex from tip of lower jaw to posterior of anal-fin base. Ventral profile of caudal peduncle concave. Prepelvic region transversely flattened proximate to pelvic-fin insertion. Distinct median keel present between pelvic-fin insertion and anus.

Head profile pointed. Mouth terminal. Snout length greater than horizontal width of orbit. Nares of each side of head close to each other; anterior nares circular, posterior nares crescent shaped. Adipose eyelid present but only slightly developed anteriorly, and with major part of eye uncovered. Lips fleshy, moderately developed, and forming oral disk when protracted.

Functional teeth in two rows in each jaw. All teeth movably implanted in flesh that overlies jaws. All teeth of similar size, with exposed portion spoon shaped except when worn down. Inner tooth series in each jaw with 13 to 20 teeth on left side of upper jaw and 7 to 10 teeth on left side of lower jaw. Outer row of teeth in each jaw with approximately 78 teeth on each side of upper jaw and approximately 75 teeth on each side of lower jaw in lectotype. Upper and lower lips bordered by numerous globular, fleshy papillae.

Scales spinoid. Scales in middorsal series between posterior of dorsal-fin base and adipose-fin origin similar in form to those of adjoining regions of body. Lateral line with 46 to 51 (42.9% of specimens with 47) pored scales; 9 to 13 (42.0% of specimens with 10) horizontal rows of scales between dorsal-fin origin and lateral line; 8 to 11 (49.0% of specimens with 9) horizontal rows of scales between pelvic-fin insertion and lateral line; 7 to 9 (60.0% of specimens with 8) horizontal rows of scales between anal-fin origin and lateral line; 15 to 22 (32.7% of specimens with 16) median predorsal scales; 14 to 18 (33.3% of specimens with 16) scales in middorsal series between posterior of dorsal-fin base and adipose-fin origin; 16 to 25 (24.5% of specimens with 22) horizontal rows of scales around caudal peduncle.

Dorsal fin preceded by small, but well-developed, anteroventrally bifurcate, procumbent spine somewhat triangular in lateral view. Dorsal-fin rays (including procumbent spine) iii,10 [iii,10]; anal-fin rays iii,8 or 9, or ii,8 or 9 (iii,8 most frequent) [iii,8]; pectoral-fin rays i,13 to 16 (i,14 most frequent) [i,14]; pelvic-fin rays i,7 to 9 (i,8 most frequent) [i,8]; principal caudal-fin rays 10/9 [10/9].

Vertebrae 41 to 43 (72.7% of specimens with 42).

Dorsal fin truncate and gently pointed distally; posterior unbranched and anterior branched rays longest and subequal. Dorsal-fin origin located closer to tip of snout than to caudal-fin base. Greatest length of adipose fin approximately four-fifths of horizontal width of orbit. Adipose-fin origin located along vertical that passes through posterior one-third of anal-fin base. Pectoral fin distally pointed. Tip of adpressed pectoral fin extending posteriorly to, or almost to, pelvic-fin insertion. Pelvic fin falcate. Pelvic-fin insertion located along vertical that passes through posterior one-third of dorsal-fin base. Tip of adpressed pelvic fin extending posteriorly approximately four-fifths of distance between pelvic-origin insertion and anus. Axillary scale present, its length approximately one-third of greatest length of pelvic fin. Posterior unbranched and anterior branched anal-fin rays longest and subequal. Caudal fin moderately bifurcate.

COLORATION IN ALCOHOL.—Ground coloration silvery yellow or brownish yellow, with dorsal portion of body and head darker. Lateral surface of body with approximately 8 to 18 (most frequently 13) dark, irregular, diffuse patches between head and caudal fin; patches with overall approximate form of narrow isosceles triangles, with apexes positioned in middle of ventrolateral portion of body and bases on dorsomedial region of body. Patches well developed in small specimens but indistinct or absent in large individuals. Lateral surface of body with approximately 13 to 18 (most frequently 14) dark, wavy, horizontal stripes along dorsal and ventral margins of exposed portions of scales. Approximately 5 to 8 (most frequently 5) dark, wavy stripes above lateral line, and 7 to 10 (most frequently 8) dark, wavy stripes below. Field of black and brown chromatophores forming dark mark of irregular shape on upper one-half of opercle.

Dorsal fin with 5 or 6 (most frequently 5) dark, irregular stripes starting along anterior margin and extening across fin approximately parallel to fin base. Adipose fin with small dark marks and dorsal border dusky. Pectoral, pelvic, and anal fins hyaline to dusky. Caudal fin with 2 to 5 (most frequently 3) [4] irregular or wavy, vertical bars formed by groups of dark chromatophores. Iris yellowish silver, with diffuse dusky areas on dorsal and ventral portions.

DISTRIBUTION.—Prochilodus lacustris is only known from the Rio Mearim and Rio Parnaíba basins, northeastern Brazil (Figure 43, triangles).

COMMON NAME.—Curimatã (Brazil).

COMPARISONS.—The combination of the presence of distinct, dark, caudal-fin pigmentation, the possession of cruciform but not elaborate subdivisions of the scales, and various meristic and morphometric features unequivocally distinguish Prochilodus lacustris from all of its congeners with the exception of P. brevis. The number of horizontal rows of scales between the pelvic-fin insertion and the lateral line demonstrate only a limited degree of overlap between P. lacustris and P. brevis, with P. lacustris having 8 to 11 scales in that series with only 8 of 51 specimens from which that count was taken having 8 scales, whereas P. brevis has 6 to 8 scales in that series with only 3 of the 59 specimens from which that count was taken having 8 scales in that series (see also Figure 36). The two species, both endemic to northeastern Brazil, also demonstrate distinctly different, albeit overlapping, ranges in the number of lateral-line scales (Figure 37). Because of the cited differences in these features and the allopatry of the populations, they are considered to be distinct species herein.

MATERIAL EXAMINED.—59 specimens (53, 57.2–324.3 mm SL).

BRAZIL. Maranhão: Rio Medonho, NMW 56618, 2 (2, 134.9–159.3). Caxias, NMW 56621, 1 (103.6). Rio Grajaú, MZUSP 5064, 9 (9, 57.2–111.0), MZUSP 20693, 2 (cleared and counterstained for bone and cartilage). Lago de Viana, Viana, MZUSP 36460, 4 (4, 168.0–250.0). Piauí: Lago de Parnaguá, Parnaguá, Rio Gurguéia system, NMW 56623, 1 (59.1); NMW 56674:1, 1 (123.1, paralectotype of Prochilodus lacustris) [1R]; NMW 56674:2, 1 (100.1, paralectotype of Prochilodus lacustris) [IR]; NMW 56674:3, 1 (85.0, paralectotype of Prochilodus lacustris) [1R]; NMW 56674:4, 1 (124.6, lectotype of Prochilodus lacustris) [1R]; NMW 56674:5, 1 (118.6, paralectotype of Prochilodus lacustris) [1R]. Teresina, MZUSP 36452, 11 (10, 148.6–198.8); NMW 56712:1–3, 3 (2, 189.4–264.2); NMW 56713, 2 (2, 155.1–227.6). Teresina, Rio Parnaíba, MZUSP 4634–37, 4 (4, 63.6–201.0); MZUSP 5104, 6 (6, 58.0–82.2). Barra do Longá (near Buriti do Lopes), Rio Parnaíba, MCZ 46810, 3 (1, 85.0–87.0) [2R]. Lagoa da Missão, NMW 56609:1–3, 3 (3, 205.3–324.3). Campo Maior, Rio Sorubim, tributary of Rio Longá, Fazenda Água Limpa, near highway BR 343, MZUSP 74953, 3 (3, 105.0–108.0).