Diagnosis: Distichodus polli can easily be distinguished from D. affinin, D. altus, D. decemmaculatus, D. hypostomatus, D. kolleri, D. noboli, D. notospilus and D. teugelsi, by its higher number of lateral line scales anterior to the hypural joint, 63-70 vs. 37-49, except 53-60 in D. hypostomatus; and from D. engycephalus and D. nefasch by its lower number of lateral line scales, 63-70 vs. 73-86 in D. engycephalus and 80-110 in D. nefasch (Ref. 122090). It can be distinguished from D. antonii, D. brevipinnis, D. lusosso, D. mossambicus, D. petersii and D. rostratus by its inferior mouth vs. terminal; moreover, it can be distinguished from D. antonii by its number of scales between the dorsal fin and the lateral line, 13-16 vs. 10-12, around the caudal peduncle, 23-26 vs. 20-23, and on the lateral line anterior to the hypural joint, 63-70 vs. 52-64; it is further distinguished from D. lusosso by its short snout vs. elongate, and a brown-greenish overall life colour pattern with 11-16 black vertical bars on the flanks on specimens smaller than about 165 mm standard length, vs. orange to reddish life body colouration with 6-8 black vertical bars (Ref. 122090). It can be distinguished from D. rufigiensis by its higher number of drosal-fin rays, 23-27 vs. 19-20 (Ref. 122090). It differs from D. maculatus, D. sexfasciatus, D. atroventralis, D. ingae and D. kasaiensis by its brown-greenish overall colour pattern with 11-16 black vertical bars for specimens smaller than about 165 mm standard length vs. numerous large round spots at all sizes in D. maculatus, 6-9 black vertical bars at all sizes and reddish colour in life in D. sexfasciatus, and 6-9 black vertical bars at all sizes in D. atroventralis, D. ingae and D. kasaiensis (Ref. 122090). Distichodus polli is most similar to D. fasciolatus, D. langi and D. schenga; it differs from D. fasciolatus by having the ventral borders of infraorbitals I and II aligned vs. ventral border of infraorbital I situated dorsal to the ventral border of infraorbital II, its higher number of pelvic-fin rays, 11 vs. 10, and a short anal-fin base, 9.4-10.4% of standard length vs. 11.3-13.7%; in addition, their colour pattern also differs; living and preserved specimens of D. polli have a black pelvic fin vs. orange pelvic fin in living and pale to beige fins in preserved specimens of D. fasciolatus, a caudal fin with a well-marked whitish hyaline distal band vs. a black distal band in D. fasciolatus, and a well-marked black hypural spot in specimens of less than about 110.0 mm standard length vs. never a black hypural spot in D. fasciolatus; furthermore, D. polli can be distinguished from D. langi by its blunt snout vs. pointed; the upper border of the posterior portion of the maxilla not overlapping or being overlapped by the ventral border of infraorbitals I and II vs. posterior portion covered by or covering the ventral border of infraorbitals I and II; and its fewer pored scales on the caudal fin posterior to the hypural joint, 3-9 vs. 14-20; besides, D. polli has narrow vertical black bars on its body, generally spanning two scales each vs. usually spanning three scales in D. langi; finally, D. polli can be distinguished from D. schenga by its height of the dorsal fin, 21.5-26.6% of standard length vs. 29.1-41.6%, the length of the longest ray of the upper lobe of the caudal fin, 25.0-31.7% of standard length vs. 32.8-41.0%, and the caudal fin with hyaline border in live specimens vs. a blackish border (Ref. 122090).

Description: Body weakly elongated and laterally compressed; dorsal profile straight from distal tip of snout up to above nostrils and convex from this point onwards to anterior base of dorsal fin; body profile between dorsal fin and adipose fin straight; region between adipose and caudal fin slightly concave; ventral profile straight from mouth to posterior border of branchiostegal membrane concave from this point to anal-fin insertion; area between anal and caudal fins weakly convex (Ref. 122090). Body covered with numerous small ctenoid scales extending over proximal two-thirds length of caudal fin and adipose fins (Ref. 122090). Mouth inferior in specimens of all sizes; two rows of teeth on both jaws, outer and inner rows with bicuspid teeth (Ref. 122090). Dorsal fin with slightly convex distal edge; its origin clearly anterior to pelvic-fin origin and near vertical through tip of longest pectoral-fin ray; dorsal fin origin located at about equal distance between tip of snout and caudal fin base or slightly closer to caudal fin base than to tip of snout; adipose fin insertion at equal distance from dorsal-fin end and caudal-fin base or slightly closer to caudal base than to dorsal-fin end; caudal fin forked with tips of upper and lower lobes slightly rounded; longest ray of upper lobe slightly longer than that of lower lobe; anal fin with slightly concave distal margin; its height larger than its base length; anterior rays longer than posterior ones, and when inclined towards caudal peduncle not reaching caudal-fin insertion; pectoral fin of same length or slightly longer than pelvic fin; distal end of pectoral fin reaching or not vertical through dorsal-fin origin and situated at mid-distance from pectoral-fin and pelvic-fin insertions; pelvic-fin insertion situated at vertical through anterior half of dorsal-fin base, its tip rarely reaching anterior border of anus (Ref. 122090).

Colouration: Preserved specimens brownish on flanks and dorsum of head and body; and light brownish to beige on ventral half of head and body; vertical dark brown bars and large black spot on caudal peduncle; largest specimens lacking black spot on caudal peduncle, suggesting that spot present in specimens smaller than 125.0 mm standard length fades during growth; adipose fin hyaline distally, with a small black stripe on distal border; pelvic and anal fins black; anal fin sometimes with a hyaline band in the distal part; caudal fin light brown with hyaline distal border, which is darker in largest specimens (Ref. 122090). Colour in life: body colour dark brown-greenish above lateral line, becoming lighter below lateral line and whitish on belly; flanks with 11 to 16 vertical black bars and large black spot on caudal peduncle; dorsal fin dark grey on its proximal third and hyaline on its distal two thirds, with numerous small black spots between fin rays; adipose fin dark grey on proximal two thirds, with a hyaline band towards its distal end, sometimes bordered by a narrow black distal band; pectoral and pelvic fins hyaline on distal third and blackish over their proximal two thirds with pelvic fin being darker than pectoral fin; anal fin yellowish-black on proximal half and hyaline on its distal half; caudal fin yellowish-black over its proximal two thirds and whitish, hyaline over distal third (Ref. 122090).