The diamond darter (Crystallaria cincotta) is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches.

[4][5] Diamond darters have 11 to 13 spines on their dorsal fins, and 11 to 15 soft rays.

Diamond darters differ in that they have a gape equal to or larger than the width of the base of their interpelvic fins,[6] which are shaped like sickles.

[3] Because of river alterations, and problems with water quality, the diamond darter's range has become greatly diminished.

[3] The effect of the 2014 Elk River chemical spill to the diamond darter is still unknown.