Diagnosis: Ambassis dussumieri has the following combination of characters: supraorbital spines 1-5, usually 3-4; rostral spine present; rear margin of preopercle smooth (at least dorsally); interopercle edge smooth; two rows of cheek scales; predorsal scales 13-16; lateral line discontunuous; lower gill rakers 22-25; pectoral-fin rays 14-16 (Ref. 50956).

Description: Dorsal fin with 7-8 spines and 8-10 soft rays; anal fin with 3 spines and 8-11 soft rays; pectoral fin with 14-16 rays (Ref. 50956, 52193). Lateral line with 12-14+10-16 scales, interrupted below base of soft dorsal rays by 1-3, usually 2, tubeless scales; vertical scale rows 27-28; horizontal scale rows 9-10; cheek scale rows 2; predorsal scales 13-16, 11 or 12 in some early juveniles (Ref. 50956). Gill rakers 8-10+22-25 (Ref. 50956). Supraorbital spines 1-4, more numerous and more pronounced in larger specimens; preorbital ridge smooth or with 2-3 small serrae; preorbital edge with 4-6 serrae (2 in 17 mm juvenile); retrorse rostral spine present at all sizes; preopercle ridge with 3-13 serrae; lower edge of preopercle with 6-31 serrae, these extending dorsally along rear margin of preopercle to about one-third its height in larger specimens; interopercle smooth except for 1-2 tiny spines near posterior angle (Ref. 50956).

Colouration: Live colouration dusky grey and translucent dorsally and posteriorly, especially in young, silvery ventrally; membrane around second and between second and third dorsal-fin spines black; scales on dorsum edged in blacl; black lineations along base of dorsal and anal fins and posterior lateral line in larger fish (Ref. 50956).