Diagnosis: Xenocharax crassus is distinguished from Xenocharax spilurus by the presence of a large black mark located anteriorly on the dorsal fin, vs. absence; a small, round, black spot at the posterior half of the caudal peduncle and covering a total of 4 to 6 scales, ±2 to 3 scales in horizontal and vertical direction alike, vs. a large ovoid spot covering a total of about 35 to 46 scales, ±8 to 10 scales in horizontal and vertical direction alike; and a wider mouth, 29-34% of head length vs. 24-29% (Ref. 114931). In addition, for the specimens of similar sizes, X. crassus has a shorter dorsal-adipose distance than X. spilurus; further, most X. crassus specimens have 6 supraneurals vs. 7 in X. spilurus (Ref. 52343, 114931).
Description: A large, robust species; body laterally compressed, relatively high, head length 28.0-33.2% of standard length, proportionally longer in smaller specimens; interorbital width broad, but overlapping range of X. spilurus; mouth terminal and wide; premaxillae with two rows of short, stout, bicuspid teeth, 32-38 in outer row; maxillae, each with 5-9 bicuspid teeth along anterodorsal margins and lower jaw with three rows of bicuspid teeth, 31-37 in outer row (Ref. 52343, 114931). Dorsal-fin origin in advance of vertical through pelvic-fin insertion; pelvic-fin origin below anterior half of dorsal-fin base approximately at level of 5th to 8th fin ray; adipose scaled basally (Ref. 114931). Scales: 74 lateral line scales, 26 transversal scales (Ref. 52343).
Colouration: In life, body generally greyish, darker dorsally over dorsal midline from head to caudal peduncle; flanks with 11-14 faint vertical bars extending from upper to lowerflanks only slightly below lateral line; in addition, flanks of some specimens variously spotted with darkly pigmented scales randomly arrayed over lower flanks below lateral line; small, round, black spot on posterior half of caudal peduncle at level of lateral line and covering a total of 4 to 6 scales, ± 2 to 3 scales in horizontal and vertical direction alike; dorsal fin dark with a large black mark anteriorly, extending over basal quarter to half of fin; pectoral and pelvic fins translucent yellowish; anal and caudal fins dark yellowish (Ref. 114931). In preservation, head and body dark brown dorsally, becoming pale yellow ventrally; opercle with large blackish blotch covering ventral region; vertical black bands clearly visible on flanks; ventral surface of head and body light yellowish-white; small, round, black spot visible at base of caudal peduncle; dorsal fin yellowish with dark patch anteriorly; pectoral, pelvic, anal and caudal fins yellowish-white to transparent with faint brownish pigmentation along or in-between rays (Ref. 114931).