The diamond darter is a member of the Perch family (Percidae), a group characterized by the presence of a dorsal fin separated into two parts, one spiny and the other soft (Kuehne and Barbour 1983, page 1). The darters differ from other percids in being much smaller in overall size and having a more slender shape. Some darters, including those in the genus Crystallaria, lack a swim bladder. This characteristic increases the density of the fish and facilitates their ability to remain near the bottom with little effort (Evans and Page 2003, page 64).