Diagnosis: The presence of supra-pectoral and supra-anal spots, which do not extend to the base of the dorsal fin, combined with a snout length longer than the post-orbital head length distinguishes this species as a member of Stigmatochromis (Ref. 87930). It is further diagnosed by the presence of mostly unicuspid teeth in the outer rows of the lower jaws; Stigmatochromis macrorhynchos has a narrower interorbital width than S. melanchros, 13.7–16.2% of head length vs. 19.3–20.5%, and a shorter snout to pelvic-fin origin than S. melanchros and S. modestus, 38.4-40.3% of standard length vs. 42.2-44.6% and 42.2-46.9% respectively; the distance between the dorsal fin origin and the posterior anal fin insertion is shorter in S. macrorhynchos, 51.2–51.8% of standard length, than in all other Stigmatochromis species, 53.5–57.2%; the distance between the anterior dorsal fin to pelvic-fin origin of S. macrorhynchos, 27.7–30.0% of standard length, is shorter than in S. modestus, 30.3–33.8%, S. woodi, 31.9–38.1%, and S. melanchros, 35.7–36.1%, and longer than in S. pholidophorus, 26.8%, and S. pleurospilus, 27.5%; the snout length of S. macrorhynchos, 38.0–41.2% of head length, is longer than in S. modestus, 33.5–37.4%, and S. pholidophorus, 37.1%; the smaller head depth of S. macrorhynchos, 59.8–63.6% of head length, further distinguishes it from S. woodi, 64.1–75.8%, and S. melanchros, 67.8–76.8% (Ref. 87930).

Description: Jaws strongly prognathous; teeth on jaws in 3 rows; teeth in outer row unicuspid; 21-26 teeth in outer row of left lower jaw (Ref. 87930). Scale rows on cheek 3; lateral-line scales 32-34; pored scales posterior to hypural plates 1-2 (Ref. 87930). Gill rakers on first ceratobranchial 10-12, with 4 on epibranchial (Ref. 87930).

Colouration: Males with dark gray head anteriorly fading to light gray/silver posteriorly; pale yellow outline of lower jaw; laterally dark blue/gray dorsally, fading to silver ventrally with 9 dark gray bars; scales with blue highlights; dorsal fin pale yellow with light yellow/white markings; blue/white lappets with dark submarginal band; caudal fin light gray with blue/white markings; anal fin with black spines and membranes; dark gray rays and membranes with light red and yellow ocelli; pelvic fins black and pectoral fins clear (Ref. 87930). Females with dark gray interorbital and white/silver cheeks and operculum; laterally, silver with yellow highlights; dorsal fin clear with faint orange marginal bar and yellow highlights; caudal fin clear with yellow markings in membranes; anal fin clear with several yellow ocelli; pelvic fin clear with white leading edge; pectoral fin clear (Ref. 87930).