The mud darter may attain a length of one and one-half to slightly over two inches. The male has dark blue bars on the rear half of the body with orange between them. Scales are present on the cheeks and gill cover. The first dorsal fin is patterned with blue at the base, red in the center and blue at the outer edge with a black blotch at the rear. The second dorsal and tail fins have light brown bands. Six to 10 dark saddles cross the brown back. The belly is white to orange. A large, dark “teardrop” mark can be seen under the eye and a dark mark from eye to snout is also present. The lateral line is incomplete. The breeding male has alternating red and blue-green bars on the sides. This fish has a life span of about three years.
The mud darter may be found statewide in Illinois. This fish lives in ditches, rivers and lowland lakes along rivers particularly in areas with sand, gravel and hard substrates that are layered with dead organic material. The mud darter spawns in spring. Eggs are deposited over debris or plants. This fish eats small crustaceans and other invertebrates.