Diagnosis: Amphilius grandis is distinguished from A. chalei, A. cryptobullatus, A. krefftii, and A. uranoscopus by the absence of distinct pale patches at the origin and insertion of the dorsal fin; it differs from A. athiensis by the absence of small dark spots on head, body, and fins, vs. head, body, and fins finely spotted, and by having shorter inner mandibular barbels, 20.2-33.6% of head length vs. 33.3-42.0%; it also differs from A. cryptobullatus and A. krefftii by its forked caudal fin vs. emarginate, and from A. krefftii by its more elongate body with 37-40 total vertebrae, vs. usually 36 total vertebrae; it also differs from A. uranoscopus by its body colouration, uniformly brown or brown with large dark spots or blotches, vs. body grey with diffuse black stripe along side; it also differs from A. chalei by having a deeper body, body depth at anus 11.0-14.4% of standard length vs. 8.9-10.8%, and a shorter caudal peduncle, caudal peduncle length 14.6-19.0% of standard length vs. 19.0-21.9%, and it also differs from A. cryptobullatus by having normally developed bilateral bony swimbladder capsules, vs. bilateral bony swimbladder capsules extremely large (Ref. 85045).

Description: Body elongate, ventral profile flattened ventrally to anal-fin base, then tapered dorsally to end of caudal peduncle; dorsal profile rising gently from tip of snout to origin of dorsal fin, then nearly horizontal to end of caudal peduncle; greatest body depth at dorsal-fin origin; caudal peduncle laterally compressed, without crenellated epidermal fond; anus and urogenital openings located at posteriormost extent of pelvic fin, closer to insertion of pelvic fin than to origin of anal fin; skin smooth (Ref. 85045). Lateral line complete, extending from dorsal edge of opercular cavity to base of caudal fin (Ref. 85045). Total vertebrae 37-40, abdominal vertebrae 20-23, caudal vertebrae 15-18; first dorsal pterygiophore intercept count 1 or 2 (Ref. 85045). Head and anterior part of body depressed and broad; head wedge-shaped in lateral view; snout broad, blunt when viewed from above; head becoming wider from tip of snout to pectoral-fin base; branchiostegal membranes moderately joined at isthmus forming a V-shaped connection (Ref. 85045). Mouth broad, gently curved, subterminal; lips moderately fleshy, papillate; rictal lobe large and papillate; anterior portion of premaxillary tooth band exposed with mouth closed; premaxillary tooth patches joined, forming U-shaped band, with short conical teeth; dentary teeth short and conical, tooth patches forming U-shaped band, separated medially (Ref. 85045). Three pairs of simple, tapered circumoral barbels; maxillary barbel large, fleshy and flattened with pointed tip; barbel extending posterolaterally from corner of mouth to just short of pectoral-fin base; outer mandibular barbel thin with pointed tip, origin at posterior corner of lower jaw, extending to origin of pectoral fin; inner mandibular barbel originates anterolaterally of outer mandibular barbel, extending to edge of branchiostegal membrane; branchiostegal membrane with 7-9 rays (Ref. 85045). Gill rakers on first epibranchial 2-3; rakers on first ceratobranchial 4-8; total gill rakers on first arch 6-11 (Ref. 85045). Eye small, positioned dorsolaterally approximately midway between tip of snout and posterior margin of operculum; horizontal diameter of eye slightly wider than vertical diameter; eye without free orbit; covered with skin confluent with dorsal surface of head; anterior and posterior nares with prominent tubular rims; nares separate but relatively close to each other; posterior nare located about midway between eye and tip of snout (Ref. 85045). Dorsal-fin origin at point over tip of pectoral fin; dorsal fin with 1 unbranched and 6-7 branched rays, and fin margin straight; pectoral fin with 1 unbranched and 9-11 branched rays with first ray unbranched and greatly thickened; pectoral fin with 4 or 5 innermost rays progressively shorter making posterior fin margin rounded; pelvic fin inserted posteriorly to dorsal-fin base; pelvic fin with 1 unbranched and 5 branched rays with first ray unbranched and greatly thickened; pelvic fin with straight posterior margin; adipose-fin base longer than anal-fin base origin anterior to origin of anal-fin base, fin extending past anal-fin insertion; margin strongly convex with sharply rounded edge, not deeply incised posteriorly; caudal fin deeply emarginate or forked with tips of lobes pointed; fin with i,7-8,8-9,i principal rays; anal fin with short base, origin posterior to origin of adipose-fin base, with 3 unbranched and 6 branched rays; anal fin margin almost straight (Ref. 85045).

Colouration: Dorsal and lateral surfaces of head and body brown; dorsal and lateral regions of head and body sometimes with large black spots or blotches; ventral region of head dark yellow; ventral region of body brown to dark yellow; light dorsal saddles absent; dorsal, adipose, caudal, and anal fins brown; pectoral and pelvic fins positioned horizontally with upper surfaces brown with light distal edge and lower surfaces light yellow; dorsal and caudal fins often with medial bands of dark pigment; maxillary and mandibular barbels brown; caudal fin with dark crescent-shaped band at base (Ref. 85045).