Key to the species of Johnius in the East Malaysian waters

1a. Chin with barbel............................................................ J. amblycephalus (Bleeker, 1855)

1b. Chin without barbel................................................................................... 2

2a. Upper jaw and inner row of lower jaw teeth enlarged, conical.................................................. 3

2b. Upper jaw and inner row of lower jaw teeth uniform, molariform............................................... 4

3a. Snout rounded............................................................... J. plagiostoma (Bleeker, 1850)

3b. Snout pointed................................................................. J. borneensis (Bleeker, 1851)

4a. Body dark pigmented; lower fins black............................................... J. belangerii (Cuvier, 1830)

4b. Body silvery to light yellow; lower fins pale................................................................ 5

5a. Scales moderately small, upper scale rows 7–11, lower scale rows 11–17......................................... 6

5b. Scales large, upper scale rows 4–7, lower scale rows 6–14..................................................... 7

6a. Gill rakers on the 1 st arch slender and long, 9–12 gill rakers on the lower limb of 1 st arch with length longer than half of gill filaments length.................................................................. J. coitor (Hamilton, 1822)

6b. Gill rakers on the 1 st arch stiff and short, 7–9 gill rakers on lower limb of 1 st arch with length shorter than half of gill filaments length........................................................................ J. weberi (Hardenberg, 1936)

7a. Lower jaw with inner row of molariform teeth posteriorly............................. J. macrorhynus (Mohan, 1976)

7b. Lower jaw teeth all conical, uniform in size................................................................ 8

8a. Total outer gill rakers of 1st arch 16–18................................................ J. carouna (Cuvier, 1830)

8b. Total outer gill rakers of 1st arch 13–15.................................................................... 9

9a. Total outer gill rakers of 1st arch (mode 12) with lower limb of 8–10 (mode 8), total scale rows 8–11 (mode 8) respectively................................................................................ J. trewavasae Sasaki, 1992

9b. Total outer gill rakers of 1st arch (mode 14) with lower limb 8–11 (mode 9–10), total scale rows 9–20 (mode 15) respectively. .................................................................................................. 10

10a. Gill rakers of outer gill rakers of 1st arch at the upper limb, 4–5 (mode 4) and lower limb 9–11 (mode 10) respectively.................................................................................... J. heterolepis Bleeker, 1873

10b. Gill rakers of outer gill rakers of 1st arch at the upper limb, 4–6 (mode 5) and lower limb 8–10 (mode 9) respectively..................................................................................... J. sasakii Hanafi et al. 2022