Key to identification of Triportheus from the Paraná-Paraguai basin

1a. Scales along predorsal line, between tip of supraoccipital and dorsal fin origin, irregularly disposed (not forming a single, continuous line) (Fig. 14A) .................. 2

1b. Scales along predorsal line, between tip of supraoccipital and dorsal-fin origin, in a single series (a maximum of two scales slightly offset from the main series) (Fig. 14B) ..................................................................................................................... 3

2a. Perforated lateral-line scales, 33–37 (mode = 34); 38–48 (mode = 43) gill rakers on the lower branch of the first branchial arch........................................ T. nematurus

2b. Perforated lateral-line scales, 28–32 (mode = 31); 26–32 (mode = 28) gill rakers on the lower branch of the first branchial arch....................................... T. pantanensis

3a. Gill rakers on the lower branch of the first branchial arch, 37–44 (mode = 44).................................................................................................... T. signatus

3b. Gill rakers on the lower branch of the first branchial arch, 33 or fewer .... T. claudiae