Diagnosis: Ambassis natalensis has following combination of characters: supraorbital spines 1-4; rostral spine absent; rear margin of preopercle entirely serrate; preopercle ridge smooth except for 1-5 tiny spines at rear corner; interopercle smooth or with 1-4 tiny serrae at angle; two rows of cheek scales; predorsal scales 9-11; lateral line continuous; lower gill rakers 19-22; pectoral-fin rays 14-15; teeth on vomer and palatines in 2-3 rows (Ref. 50956).

Description: Dorsal fin with 8 spines and 9-11 soft rays; anal fin with 3 spines and 9-11 soft rays; pectoral fin with 14-15 rays (Ref. 4318, 50956, 52193). Lateral line usually continuous, with 27-29 scales, several specimens from Mauritius with lateral line interrupted by 2-3 scales on one or both sides; vertical scale rows 28-30; horizontal scale rows 9-10; cheek scale rows 2; predorsal scales 9-11 (Ref. 50956, 52193). Gill rakers 8-10+19-22 (Ref. 4318, 50956). Supraorbital spines 1-4, more numerous in largest specimens; preorbital ridge smooth in smallest specimens, becoming serrate at about 35 mm standard length; preorbital edge with 5-11 serrae; retrorse rostral spine absent; preopercle ridge smooth except for 1-5 small spines at lower rear corner; lower edge of preopercle with 9-18 serrae, rear margin enirely serrate; interopercle with 1-4 minute spines at angle (Ref. 50956). Teeth in villiform bands on vomer, palatines, tongue and jaws; palatine teeth in 2-3 rows in fish over about 20 mm standard length (Ref. 50956).

Colouration: Live colouration translucent greenish-brown dorsally, head and abdomen silvery; scales with minute melanophores; membrane between second and fourth dorsal-fin spine dusky, black at tip; black lineations along bases of unpaired fins (Ref. 50956).