The dusky darter may attain a length of two to four inches. The back and upper sides are green to brown to black, the back having eight to nine dark saddles. Wavy, dark lines are present on the upper sides. Each side has eight to 12 oval, dark blotches. The lower sides and belly are white. Usually there is no dark, “teardrop” mark under the eye. The fins are clear, although there may be a dark spot at the rear of the first dorsal fin, and the second dorsal and tail fins may have light brown lines. The base of the tail fin has three dark spots, the lower two sometimes connected. The bone just in front of the gill cover is saw-toothed along the edge. The gill covers are connected by a membrane across the throat. The lateral line is complete. This fish has an average life span of about three years.
The dusky darter may be found from east central Illinois through the Ohio River border counties. This fish lives in creeks and rivers over a silt-free, sand or gravel bottom, often among brush, leaves or other organic debris. The dusky darter spawns in spring or summer depending on the water conditions. The eggs are mixed into the substrate. No parental care is given. This fish eats immature insects.