Pirate perch are unusual in that their urogenital opening is positioned far anteriorally under the throat (Fletcher, et. Al. 2004). This feature is not present in juveniles, as the anus migrates with maturity. Pirate perch are grayish with black speckles and have a narrow, vertical, dark bar at the base of the tail fin and under the eye (Pflieger, 1975). Pirate perch have a single dorsal fin and ctenoid scales on the head and body. The tail fin is slightly notched, not deeply forked. The gill cover has a sharp spine. Dorsal and anal fins each have 2 or 3 weak spines at front (Pflieger, 1975). The mouth is moderately large with a slightly projecting lower jaw (Clay, 1962). The lateral line is incomplete or underdeveloped in pirate perch from the Midwest, but specimens closer to the Atlantic coast show a much better developed lateral line (Eddy, 1969). Pirate perch are sexually dimorphic with females being larger and more full-bodied than males (Tiemann, 2004).
Range length: 6.35 to 12.7 mm.
Average length: 6.1 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently