Diagnosis: Enteromius thespesios belongs to the group of Enteromius species from the Congo basin of which the last unbranched dorsal-fin ray is weakly ossified, flexible and lacking serrations along its posterior edge (Ref. 122753). It can be easily distinguished from all other members of this group by the following unique combination of characters: two pairs of barbels vs. no barbels in Enteromius aspilus, E. baudoni, E. brazzai, E. carens, E. erythrozonus, E. haasianus, E. jae, E. stigmatopygus and E. toppini and a single pair of barbels in Enteromius brevidorsalis, E. candens, E. hulstaerti, E. nigrifilis, E. owenae, E. papilio and E. syntrechalepis; one prominent dark vertical bar situated behind gill-opening vs. a series of 10-15 black vertical bars on body in E. fasciolatus; no spots on flanks vs. well-defined spots on flanks in E. atromaculatus, E. barotseensis, E. camptacanthus, E. castrasibutum, E. collarti, E. lornae, E. lukusiensis, E. neefi, E. stanleyi, E. tetrastigma, E. trispilomimus and E. urostigma; a series of crescent-like spots along lateral line vs. a well-marked continuous black band running from snout to caudal fin base in E. ablabes, E. luluae, E. kessleri, E. lamani, E. macrops and E. radiatus; lateral line complete vs. lateral line incomplete in E. brachygramma and E. lujae; 23-26 lateral line scales vs. 21 in E. okae, 21-22 in E. pygmaeus, 20-22 in E. stigmasemion, 27-29 in E. bifrenatus, 30 in E. caudosignatus, 29-32 in E. cercops, 28 in E. citrinus, 32-33 in E. deguidei, 29-33 in E. innocens, 27-30 in E. kamolondoensis, 30-32 in E. lineomaculatus, 28-29 in E. marmoratus, 32-33 in E. mocoensis, 33-37 in E. motebensis, 31-33 in E. poechii, 27-30 in E. quadrilineatus, 27-29 in E. taeniopleura and 29-35 in E. unitaeniatus; and 11-12 circumpeduncular scales vs. 8-10 in E. amanpoae, 10 in E. humeralis and 8 in E. lufukiensis (Ref. 122753). Enteromius thespesios differs from E. tshopoensis by a long dorsal-fin length, 27.1-35.6% of standard length, vs. shorter, 22.3-24.0% of standard length, and by a large body depth, 29.4-34.1% of standard length, vs. smaller, 18.0-20.4% of standard length; it differs from E. validus by a dorsal fin without a conspicuous black tip vs. dorsal fin with a conspicuous black tip, a small eye diameter, 25.5-33.1% of head length, vs. larger, 37.2-46.9% of head length, and a small body depth, 22.2-24.6% of standard length, vs. larger, 26.3-35.5% of standard length (Ref. 122753). Finally, E. thespesios besides its high number of circumpeduncular scales, 11-12 vs. lower, 10, is further distinguished from E. humeralis by its small eye diameter, 25.5-33.1% of head length, vs. larger, 33.8-41.2% of head length; short anterior barbel length, 22.2-33.1% of head length, vs. longer, 35.1-45.0% of head length; short posterior barbel length, 25.9-32.0% of head length, vs. longer, 34.2-44.6% of head length, and its short, dorsal fin length, 22.3-24.0% of standard length, vs. 24.0-27.3% of head length (Ref. 122753).
Description: Rather small-sized species of Enteromius, with a maximum recorded size of 62.3 mm standard length for females and 60.7 mm standard length for males (Ref. 122753). General body shape fusiform; body depth greatest anterior to dorsal fin; profile of predorsal region of body slightly convex (Ref. 122753). Mouth subterminal; eyes relatively small, located laterally, that is, visible from both above and below, closer to tip of snout than to the posterior region of operculum; interorbital profile flat (Ref. 122753). Anterior barbel usually slightly shorter than posterior barbel with anterior one reaching up to anterior border of eye while posterior one up to centre of eye (Ref. 122753). Dorsal-fin origin located at midbody and slightly anterior, 1 or 2 lateral line scales, to vertical through pelvic-fin insertion; distal margin of dorsal fin straight; first branched dorsal-fin ray longest, posterior rays decreasing progressively in size; distal profile of pectoral fin straight to slightly convex, not reaching anterior base of pelvic fin; distal profile of pelvic fin convex; distinct axillary pelvic scale pointed; caudal fin forked with outer rays twice as long as median ones and both lobes rounded and of similar size; anus and genital opening situated immediately in front of anal-fin base; size and shape of anal fin and pelvic fins sexually dimorphic (Ref. 122753). Scales cycloid, rounded and radially striate; lateral line gently curved downwards over abdomen but running straight along middle of caudal peduncle and ending at base of caudal fin; lateral-line scales smaller on caudal peduncle than below dorsal fin (Ref. 122753).
Colouration: In life, overall background body colouration variable and seemingly different between sexes; in general, background body colouration yellowish, darker towards dorsal midline and lighter towards belly; snout, upper jaw and dorsal part of head dark brownish while remaining part of head bright yellow; scales of lateral line and above with distinct black melanin mark covering 1/3rd of its proximal base; at level of lateral-line scales, inconspicuous black band in male specimens or silver band in female specimens runs from upper end of operculum to centre of caudal-fin base; all fins yellowish with white translucent distal margin (Ref. 122753). However, background body colouration more intense in mature breeding males than in mature breeding females; in addition, dorsal and caudal fins of males yellowish near ray insertions, followed by black band and red band toward their distal edge, bordered by a narrow translucent band (Ref. 122753). In preserved specimens, ground colour greyish dorsally and whitish ventrally and laterally below the lateral line; all red and yellowish colouration gradually disappears but the traces of the black band persist on the dorsal and caudal fins; a well-marked, black, mid-lateral band along lateral line becomes apparent; all fins whitish; black band on dorsal fin persists only on specimens freshly preserved in alcohol (Ref. 122753).