Diagnosis: Micropanchax petnehazyi is distinguished from all other Micropanchax species, with the exception of M. hutereaui, by the combination of following characters in male colouration: dark transverse markings on the median fins; reticulate markings on the side; as well as the structure of the cephalic sensory system in both sexes characterised by a supraorbital canal composed of two short, discontinuous grooves containing exposed neuromasts; postorbital and preopercular sensory systems tubular with pores (Ref. 122040). Furthermore, M. petnehazyi is distinguished from M. hutereaui by the following unique combination of characters in males: dorsal and anal fins with faint brown stripes perpendicular to fin rays vs. curved stripes in M. hutereaui; anal fin with a faint brown margin and without a light submarginal band vs. with dark brown margin and with light submarginal band; caudal fin with irregular vertical markings forming a reticulate pattern vs. narrow vertical bands; as well as, in both sexes, preorbital sensory system in a shallow canal with three exposed neuromasts vs. tubular with three pores; mandibular sensory system in open groove with small exposed neuromasts vs. tubular with pores; smaller body depth at pelvic-fin origin 25.3-28.7% of standard length vs. 30.0-32.3%; smaller interorbital width 34-40% of standard length vs. 47-51%; larger postorbital length 45-46% of head length vs. 38-43%; smaller suborbital depth 11-14% of head length vs. 21-25%; and larger caudal peduncle length 1.4 times of its depth vs. 1.0-1.1 (Ref. 122040).

Description: General body shape slightly laterally compressed and moderately deep; small-sized species; greatest vertical body depth in front of pelvic-fin origin and shallowest at mid-portion of caudal peduncle; greatest body width at pectoral-fin base with body progressively narrowing towards caudal-fin base (Ref. 122040). Dorsal profile slightly convex from snout to base of first dorsal-fin ray, slightly concave from base of dorsal to caudal fin; ventral profile convex from lower jaw to base of last anal-fin ray, straight to slightly concave on ventral midline of caudal peduncle (Ref. 122040). Caudal peduncle shallow, length 1.4 times its depth; ans directly in front of anal-fin origin (Ref. 122040). Head short, laterally compressed, deeper than wide, head width 68-75% of its depth; snout slightly rounded, smaller than eye diameter; mouth superior, oblique in profile; jaws not equal, lower jaw longer than upper, posterior end of corner of mouth at same level to centre of eye; premaxilla and dentary with many irregularly distributed conical teeth; orbit large, 34-38% of head length, in anterior half of head, in dorsal portion of head side (Ref. 122040). Dorsal-fin origin posterior to anal-fin origin; both fins originating posterior to mid-length of body; dorsal and anal fins rounded; pectoral fin subtriangular, insertion relatively high and slightly posterior to margin of opercular opening; base oblique, upper fin rays placed anteriorly to lower fin rays; pelvic fin short, sub-abdominal, origin at about mid-length between insertions of pectoral and anal-fins; caudal fin subtruncate (Ref. 122040). Scales cycloid, body and head entirely scaled, except for ventral surface of head; frontal squamation pattern G-type; cephalic sensory system at preorbital level in shallow groove with three exposed neuromasts; postorbital canal tubular with two pores; preopercular sensory systems tubular with seven pores; frontal neuromasts separate, lodging two neuromasts; cephalic sensory system at supraorbital level in two short discontinuous grooves with one and two exposed neuromasts; whereas at supratemporal level in a curved groove, with four exposed neuromasts; mandibular canal in shallow open grove with two small exposed neuromasts (Ref. 122040).

Colouration: Live males: scales on trunk and head yellow to light greyish brown with dark brown margin, conferring dark reticulated pattern on body sides; flank with faint light blue to silver iridescence; scales on abdomen faint light blue to silver, scales on dorsum of body greyish brown; snout and dorsal portion of head greyish brown, throat silver; exposed branchiostegal membrane white; iris silver, iridescent in upper portion; iridescent silver blotch on postorbital opercular region; iridescent blue spot on post-opercular region; narrow dark grey stripe on scales of midlongitudinal series; dorsal fin membrane yellowish hyaline, with faint brown stripes perpendicular to fin rays; anal fin membrane yellowish hyaline, with faint brown stripes perpendicular to fin rays in posterior portion; caudal fin membrane yellowish hyaline, with narrow faint brown vertical stripes perpendicular to fin rays in proximal and median portions, without coloured circumcaudal margin; pelvic fin yellowish hyaline; pectoral fin hyaline (Ref. 122040). Live females: scales on trunk and head yellow to light grey-brown, ventrally silver; flank with faint light blue to silver iridescence; narrow dark grey mid-lateral stripe on trunk; iris silver, iridescent in upper part; all fins hyaline (Ref. 122040).