Etheostoma gracile, the slough darter, is a small species of ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae which includes the perches, ruffs and pike-perches. It inhabits slow to moderately flowing waters and with substrates that are predominantly mud, silt, or sand. Major food sources include chironomids, copepods, and cladocerans, as well as mayflies in the spring. Adults reach 35 to 50 mm (1.4 to 2.0 in) total length. It is one of the 324 species of fish found in Tennessee.

At the southern end of its range in Texas, the slough darter breeds from January to March, while at the northern end of its range in Illinois, it breeds in May and June. The eggs are attached to submerged vegetation, leaves, or twigs, and the adults do not guard them as some other members of this family do.

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