Diagnosis: Mastacembelus kadeiensis differs from all other species of Mastacembelus in having 19 dorsal-fin spines; dorsal fin origin on vertebra 6; first dorsal fin pterygiophore without spine, articulating with neural spine of vertebra 6; base of first dorsal-fin spine above vertebra 8, base of last dorsal fin spine above vertebra 28, base of first anal fin spine below vertebrae 31, above 8 and 22, and below 33 in Mastacembelus sexdecimspinus; branchiostegal rays 4, usually 6 in other Mastacembelus; dorsal-fin rays 95; anal-fin spines 3, 2 much stouter and longer than 1 and 3; anal-fin rays 81; principal caudal-fin rays 5/6, no upper or lower procurrent rays; vertebrae 28+57=85 (Ref. 123814). Most similar species of Mastacembelus kadeiensis is M. sexdecimspinus; it differs from M. sexdecimspinus in having dorsal fin spines 19, vs. 15-16; dorsal-fin rays 95, vs. 112-132; anal-fin rays 81, vs. 81-98; origin of dorsal-fin soft rays above vertebrae 29, of anal-fin soft rays below 35, vs. above vertebra 23 and below 35; vertebrae 28+57=85, vs. 30+58=88 (Ref. 123814). Both have spiny dorsal fin origin above vertebra 6, apparently 4 branchiostegal rays, and 5/6 principal caudal-fin rays; colouration markedly different; that of M. kadeiensis can be compared to that of a typically-coloured M. sexdecimspinus which has entire head and body with dark background colouration closely covered with rows of numerous large roundish pale spots; such colouration is continuous over the entire dorsal and anal fins, lacking a thin white margin, and on ventral surface of head and abdomen which are much lighter in colouration overall; pectoral fin with smaller dark mark near its base and two thin broken vertical bars on its middle (Ref. 123814).

Colouration: Live colouration not recorded (Ref. 123814). Colouration of preserved specimens highly distinctive, most notably with a series of bilateral pairs of small round white spots on each side for entire length of dorsum, and 14 bold obliquely-oriented white slash marks on ventral part of body on either side just above anal fin base; dorsal surface of head to well below eye and upper half of gill cover and entire lateral surface of body uniformly dark coloured, without pale marks or pattern; ventral half of head and abdomen entirely pale, without marks or pattern, then a series of ten large sharply defined roundish or oval pale spots on either side of body above anal fin base; dorsal and anal fins darkish overall, with thin white margin; pectoral fin pale overall, with large dark blotch on its base and two thin dark vertical bars in its middle (Ref. 123814).