No fewer than 20 specimens were used for description, and the epithet crassilabrum (from the Latin crassus meaning thick or fat and labrum, or lip) was assigned to the species, separating it from Phenacobius catostomus, with which it had previously been identified.

[3] The fatlips minnow is believed to have arisen from a P. catostomus -like stock population that re-invaded the upper Tennessee River via reciprocal stream piracy.

There are documented instances of nonindigenous (out-of-range) occurrences of Phenacobius species; these are believed to be a result of fishermen releasing their unused baitfish into local bodies of water.

[citation needed] P. crassilabrum is known to favor gravel riffles in the warm clear waters of small to medium-sized streams and rivers.

Species of the genus Phenacobius remain near the bottom of streams, rooting in the ground for their prey of detritus and aquatic insects such as mayfly and caddisfly larvae.