Key to the species of Rhinogobius in Da Nang City and Thua Thien Hue Province, Vietnam

1 Predorsal scales extending anteriorly to near posterior margin of eyes; cheek with several short transverse rows of cutaneous sensory papillae, and reddish-brown dots and lines forming diagonal stripes running upward from anterior to posterior................................................................................................... R. similis

- Predorsal scales not reaching posterior margin of preopercle or ending shortly anterior to it (not reaching close to eyes); cheek without transverse row of cutaneous sensory papillae, and without diagonal stripes, or with diagonal stripes directing downward from anterior to posterior............................................................................... 2

2 When mouth closed, anterior tip of lower jaw significantly protruding beyond upper jaw in larger male (> 40 mm SL); pectoral fin usually with 19 rays; orange (male), reddish-brown, or grey (female) diagonally downward stripes on cheek..... R. rong

- Positions of anterior tips of lower and upper jaws approximately same, or upper jaw protrudes more anteriorly; pectoral fin with 18 or fewer rays (sometimes 19 in R. leavelli); cheek with three parallel, diagonally downward, reddish-brown or dusky-brown stripes (male of R. nami), or without diagonal stripes (other species)............................................. 3

3 Dark-brown vertical band at caudal-fin base often combined with larger dark-brown lateral blotch on caudal peduncle; opercular membrane, interopercle, and lower part of subopercle of male grey with many orange stripes running along margin of preopercle and opercle; first dorsal fin of male with 1–3 distinct black spots on proximal parts (not in middle) of membranes between anterior 2–4 spines; pectoral fin with 16–19 rays.............................................. R. leavelli

- Black, vertical rectangular or elliptical spot at mid-base of caudal fin; opercular membrane, interopercle, and lower part of subopercle of male light bluish-grey with many red or orange spots; first dorsal fin of male with series of black or brown markings on middle parts of membranes between first to fifth spines (anterior one or two markings usually clear); pectoral fin usually with 14–16 rays................................................................................ 4

4 Five, longitudinal, reddish-brown or dusky-brown stripes (dotted lines) running on lateral and dorsal sides from trunk to caudal peduncle; three parallel, diagonally downward, reddish-brown or dusky-brown stripes on ventral part of cheek in male; number of vertebrae usually 26............................................................................ R. nami

- Lateral and dorsal sides of body without longitudinal stripes; cheek without diagonal stripes; number of vertebrae usually 27............................................................................................ R. taenigena .