The rainbow darter (Etheostoma caeruleum) is a native North American fish found in small, fast-moving streams and small to medium-sized rivers. It grows to 2 to 3 inches (51 to 76 mm) in length. The species is very sensitive to pollution and silt, staying in clean, pollution-free water. The rainbow darter is easily identified by three dark spots on the back, and blue and orange in the dorsal and anal fins. It is a small perch-like fish found in freshwater streams in North America.
The rainbow darter is a small, benthic freshwater fish found in many creeks and small to medium-sized rivers throughout North America. In particular, it is common throughout the eastern United States, specifically throughout the Great Lakes and Ohio River Valley regions. Its distribution extends south to northern parts of Alabama and as far west as Missouri and Arkansas. This distribution has been suggested to be due to once existing glaciers and to its intolerance of brackish water. One study to examine the phylogeography of E. caeruleum and its colonization patterns found its distribution is greatly due to historic glaciations, and furthermore, due to distributions from drainages which have since then resulted in the current morphological diversity of the rainbow darter. Geographically, the rainbow darter is one of the most abundant and common darter species.