Paraschistura nielseni can be diagnosed from its congeners in Iran by a combination of non-unique characters. It differs from P. bampurensis by the presence of a suborbital groove in males (vs. presence of a suborbital flap), 6-11 dark-or pale-brown or grey bars (vs. 11-18), wider than interspaces (vs. usually narrower than interspaces), regularly set and shaped (vs. usually irregularly set and shaped) and a blunt snout (vs. pointed); from P. cristata by the absence of a dorsal adipose crest (vs. presence), the presence of a suborbital groove in males (vs. absence) and an incomplete lateral line (vs. complete); from P. kessleri by having 6-11 dark- or pale-brown or grey, irregularly set and shaped bars (vs. 10-12 bars, regularly shaped and set) and the flank and the back covered by scales (vs. scaleless). The following additional characters are useful to distinguish P. nielseni: a very deep body (body depth at dorsal-fin origin 15-17 % SL); usually dorsal fin with 7 1/2 branched rays; spot at the base of first dorsal-fin rays faint; pelvic fin reaching to about 1-2 eye diameters in front of anus (Ref. 103390).