Cyphocharax gangamon Vari 1992

Cyphocharax gangamon

DIAGNOSIS.—Cyphocharax gangamon is distinguished from its congeners by the combination of 27 or 28 scales to the hypural joint in the longitudinal scale series including the lateral line, the development of pores along the entire lateral line in all but juvenile specimens, the 28 to 30, typically 29 or 30 vertebrae, the relative length of the postorbital portion of the head (0.35–0.41 of HL), the relative length of the head (0.31–0.34 of SL), the relative width of the orbit (0.32–0.37 of HL), the absence of multiple series of longitudinal dark stripes or small dark spots in longitudinal rows on the body, the absence of a discrete patch of dark pigmentation on the dorsal fin, the presence of a patch of dark pigmentation on the midlateral surface of the caudal peduncle not preceded by 4 or 5 large midlateral dark spots on the body, the absence of a stripe of dark pigmentation across the middle rays of the caudal fin in moderate to large-sized specimens, the reticulate pattern of dark pigmentation on the body in adults, and the possession of 9 branched dorsal-fin rays.

DESCRIPTION.—(Meristics and morphometrics based just on type series; see under “Remarks” and Table 11 with respect to second evidently conspecific population from Rio Arinos, Mato Grosso.) Body moderately elongate, moderately compressed laterally in all examined specimens. Dorsal profile of head moderately convex from margin of upper lip to vertical line through posterior nostril, straight from that line to posterior of head. Dorsal profile of body smoothly curved from tip of supraoccipital spine to origin of dorsal fin; straight and posteroventrally slanted at base of dorsal fin, straight or gently convex from base of last dorsal-fin ray to caudal peduncle. Dorsal surface of body with moderately developed median keel anterior to dorsal fin, smoothly rounded transversely posterior to fin. Ventral profile of body gently curved from tip of lower jaw to caudal peduncle. Prepelvic region somewhat flattened transversely, with median series of scales of size comparable to those on adjoining portions of body. Moderately developed median keel posterior to pelvic fin origin. Secondary obtuse keels on that portion of body not evident.

Greatest body depth at origin of dorsal fin, depth 0.35–0.40 [0.40]; snout tip to origin of dorsal fin 0.50–0.55 [0.54]; snout tip to origin of anal fin 0.80–0.84 [0.84] (see also “Remarks” and Table 11 with respect to data for population from Rio Arinos); snout tip to origin of pelvic fin 0.55–0.59 [0.56]; snout tip to anus 0.75–0.81 [0.78]; origin of dorsal fin to hypural joint 0.52–0.58 [0.55] (see also “Remarks” and Table 11 with respect to data for population from Rio Arinos). Distal margin of dorsal fin rounded; last unbranched and first branched rays approximately three times length of ultimate ray. Distal margin of pectoral fin barely rounded, length of pectoral fin 0.19–0.25 [0.25], extends to or nearly to vertical line through origin of pelvic fin. Distal margin of pelvic fin rounded; length of pelvic fin 0.22–0.27 [0.27], reaches beyond anus and nearly to origin of anal fin. Caudal fin forked. Adipose fin well developed. Anal fin emarginate, anteriormost branched rays twice length of ultimate ray. Least depth of caudal peduncle 0.13–0.14 [0.13] (see also “Remarks” and Table 11 with respect to data for population from Rio Arinos).

Head profile rounded anteriorly, overall profile of head pointed; head length 0.31–0.34 [0.31]; upper and lower jaws equal, mouth terminal; snout length 0.26–0.30 [0.29]; nostrils of each side separated by distance approximately equal to longitudinal width of anterior nostril, anterior nares transversely ovoid, posterior tear-drop shaped with aperture not closed by thin flap of skin separating nares; orbital diameter 0.32–0.37 [0.33]; adipose eyelid largely absent, slightly developed anterior to orbit; length of postorbital portion of head 0.35–0.41 [0.41]; gape width 0.18–0.23 [0.22]; interorbital width 0.41–0.46 [0.43].

Lateral-line scales from supracleithrum to hypural joint 27 or 28 [28]; 8 scales of lateral line pored in specimens of about 25 mm SL, number of scales increasing in larger specimens, all scales pored in specimens greater than 32 mm SL, canals in pored lateral-line scales straight; 2 or 3 series of scales in horizontal series continuous with lateral line extend beyond hypural joint onto caudal-fin base; 4 to 5 (4 rare) [5] scales in transverse series from origin of dorsal fin to lateral line (see also “Remarks” and Table 11 with respect to data for population from Rio Arinos); 4 or 4 [4] scales in transverse series from lateral line to origin of anal fin.

Dorsal-fin rays ii,9 [ii,9]; anal-fin rays ii,7 [ii,5]; pectoral-fin rays 13 to 15 [13]; pelvic-fin rays i,7 or i,8 (i,7 in only 1 paratype) [i,8].

Total vertebrae 28 (3), 29 (32), 30 (2) (see also “Remarks” and Table 12 with respect to data for population from Rio Arinos).

COLOR IN ALCOHOL.—Type-specimens largely lacking guanine on scales, overall ground coloration light brown, with slightly silvery sheen. Upper lip, snout, and dorsal portion of head and opercle with field of small, scattered, dark chromatophores; lower jaw with field of small, dark chromatophores, most intense along margin of lower lip. Margins of scales along lateral, dorsolateral, and dorsal surface of body outlined by series of small dark chromatophores, forming reticulate pattern (Figure 72); more diffuse pattern of small dark chromatophores on dorsal portion of body giving it overall dusky appearance. Deep-lying dusky stripe running along midlateral surface of body from point under base of dorsal fin to posterior of caudal peduncle. Posterior portion of dusky stripe overlain by rotund to somewhat vertically ovoid dark spot on midlateral surface of posterior portion of caudal peduncle and basal portion of middle rays of caudal fin. Fin-rays of dorsal, caudal, and anal fins distinctly outlined by series of small, dark chromatophores. Scattered small dark chromatophores on pelvic and pectoral fins. Adipose fin dusky.

Character A B

MORPHOMETRICS

Standard Length 25.1–46.8 29.7–52.3

1. Snout to anal-fin origin 0.80–0.84 0.84–0.87

2. Snout to anus 0.75–0.81 0.80–0.83

3. Caudal peduncle depth 0.13–0.14a 0.13–0.15b

MERISTICS

Scale rows between dorsal-fin origin and lateral line 4–5c 4

a Most specimens with 0.13, average for all type-specimens 0.134.

b Most specimens with 0.14 or 0.15, average for measured specimens 0.146.

c 4 rare, most type specimens with 5 or 5 scales.

Population of Cyphocharax gangamon from Rio Arinos system much lighter in overall pigmentation (Figure 73). Reticulate pattern on lateral and dorsolateral surfaces of body barely apparent, largely hidden by residual guanine on scales. Spot of dark pigmentation on midlateral surface of caudal peduncle less intense and more diffuse, more vertically developed than in comparable sized specimens from the type locality.

DISTRIBUTION.—Rio Tapajós of Rio Amazonas basin (Figure 74, localities 1 and 2; see also comments under “Remarks” below).

ETYMOLOGY.—The species name, gangamon, from the Greek for net, refers to the reticulate pattern on the lateral and dorsal surfaces of the body in the species.

MATERIAL EXAMINED.—15 specimens (15, 25.1–46.8).

HOLOTYPE.—BRAZIL. Pará: Rio Tapajós, Monte Cristo, Lago da Santa Clara (approx. 4°04′S, 55°38′W), collected by EPA under direction of P.E. Vanzolini, 6 Dec 1970, MZUSP 22037, 1 (46.8).

PARATYPES.—BRAZIL. Pará: Rio Tapajós, Monte Cristo, Lago da Santa Clara (approx. 4°04′S, 55°38′W), 14 specimens collected with holotype: MZUSP 41752, 8 (25.2–34.0); USNM 309290, 6 (25.1–31.0; 1 specimen cleared and counterstained for cartilage and bone).

NON-TYPE MATERIAL EXAMINED.—257 specimens (25, 29.7–52.3).

BRAZIL. Pará: Rio Tapajós, Monte Cristo, Lago da Santa Clara (approx. 4°04′S, 55°38′W), collected with holotype, MZUSP 41753, 25. Mato Grosso: Rio Arinos, Porto dos Gauchos, floodplain pool (approx. 11°30′S, 57°20′W); USNM 267991, 116 (25, 29.7–52.3); MZUSP 41754, 116.

Bacia do Rio Tapajós