Rainbow darter

Distribution

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. Current distribution shown may be outdated and should be verified with state agencies. Particularly Texas where the species exists in limited number.

Habitat

The rainbow darter is classified as insectivorous, feeding on small invertebrates such as insects and crayfish, but it has also been known to feed on some fly larvae. In Four-Mile Creek in Ohio, the rainbow darter lives primarily on trichopterans , having two feeding peaks: one in the morning and a second in the late afternoon or early evening.
The primary predators of the rainbow darter are larger freshwater fish, such as burbots , stonecats , and smallmouth bass . Like many other darter species, it has the ability to maintain position on the substrate in flowing water. This unique characteristic plays a key role in its microhabitat preference. ''E. caeruleum'' has been shown to prefer creeks and rivers with rocky substrates and swift-moving riffles. This microhabitat preference has been suggested to be due to oxygen levels in the water during season changes or other factors, such as feeding or shelter-related habitat preferences. Because ''E. caeruleum'' has such a low tolerance for brackish water, human-induced changes such as pollution or sewer drainage has the potential to cause a significant negative impact on its abundance.

Evolution

Darters have a wide range of life histories, but size correlates with most life history characteristics. For example, larger darters grow faster, live longer, produce bigger clutches, and have longer reproductive spans. Mate selection by female darters is assumed to be common. When examining the rainbow darter, life history traits were: average size 45 mm, growth 32 mm, maximum age four years, and clutch size 82. ''E. caeruleum'' mates during the spring, typically when water temperature is between 17 and 18 °C, and they will leave their normal microhabitat in the rapids to congregate on pebbles, where the stream leaves a pool, to mate. Once mates are selected, the fish mate repeatedly for several days until the female lays about 800 eggs. This darter also displays group spawning, and the males tend to exhibit territorial behavior during the breeding season.