The rainbow darter is a native North American fish that can be found in small fast moving streams and small to medium-sized rivers. It grows to 2 inches (51 mm) to 3 inches (76 mm) in length.

The Etheostoma caeruleum is very sensitive to pollution and silt, staying in clean pollution-free water.

Rainbow darters are easily identified by three dark spots on the back; also they have blue and orange in their dorsal and anal fins.

Life

The Etheostoma caeruleum spawns in clean rocky riffles March through June. Etheostoma caeruleums live to be about 4 years of age.

The world's largest Rainbow Darter was caught summer 2010 just outside of Barrie Ontario, measuring 80 mm in length. It was caught and released.

Abstract

The purpose of this paper is to portray a feasible monitoring plan for the Rainbow darter (Etheostoma caeruleum). Modern societies are constantly expanding, therefore, increasing the amount of waste and byproducts that accumulate in lakes and rivers. This ultimately results in contamination and can greatly impact fish habitats across the globe, specifically those inhabited by Etheostoma caeruleum. Other members of the Etheostoma genus have become endangered due to such urban landscapes. Therefore it is extremely important to develop a management plan in order to prevent the endangerment and possible extinction of Etheostoma caeruleum. The proposed management plan in this paper will stem from basic understanding of Etheostoma caeruleum’s geographic distribution, ecological aspects (i.e. diet, prey, and predators), life history, and any current management plans that have already been instituted.
Examination of the types of climate zones as well as specific types of streams and lakes that E. caeruleum occupies will allow proper evaluation of any urban threats to the species’ survival. Important ecological aspects such as stream velocity preference as well as life history traits such as reproductive cycles will also be examined to expose possible threats to E. caeruleum. The basic understanding of such key characteristics is necessary in order to prevent invasive species and habitat destruction. Lastly, any current management plans in place for other members of the Etheostoma genus or similar species should be examined in order to properly assign measures that can accurately protect Etheostoma cauruleum as seen by past successes and failures of conservation attempts. Ultimately, a solid management plan for Etheostoma caeruleum is necessary to prevent endangerment and possibly extinction, as seen by many other darter species. Understanding as many characteristics as possible will ultimately result in a stronger management plan that should last and preserve the species diversity in the Etheostoma genus.

Geographic Distribution

The rainbow darter, Etheostoma caeruleum, is a small, benthic freshwater fish. It can be found in many creeks and small to medium sized rivers throughout North America. In particular, E. caeruleum 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 to Missouri and Arkansas (Kuehne and Barbour 2006). This distribution has been suggested to be due to once existing glaciers and to E. caeruleum’s intolerance to brackish water. One study examined the phylogeography of E. caeruleum and its colonization patterns and found that 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 (Ray et al. 2006). Geographically, E. caeruleum is one of the most abundant and common darter species.

Ecology

Some important ecological characteristics of the rainbow darter are its diet, predators, and microhabitat preferences. Etheostoma caeruleum are classified as insectivores, feeding on small invertebrates such as insects and crayfish, but they have also been known to feed on some fish larvae. One study examined the diet of three darter species in Four-Mile Creek in Ohio, including E. caeruleum and found that the rainbow darter survived primarily on Trichopterans (i.e. caddis flies), having two feeding peaks: one in the morning and a second peak in the late afternoon or early evening (Adamson and Wissing 1977).
Following the food web, it makes sense that the primary predators of E. caeruleum are larger freshwater fish such as burbots (Lota lota), stonecats (Notorus flavus), and smallmouth bass (Micropterus dolomieu) (Kuehne and Barbour 1983).E. caeruleum, like many other darter species have the ability to maintain position on the substrate in flowing water (Carlson and Lauder 2010). This unique characteristic plays a key role in its microhabitat preference. In regards to microhabitat, E. caeruleum has been shown to prefer creeks and rivers that have a rocky substrate and swift moving riffles (Harding et al. 1998). This microhabitat preference has been suggested to be due to oxygen levels in the water during season changes or simply due to other factors such as feeding or shelter related habitat preferences (Harding et al. 1998). Because E. caeruleum has such a low tolerance for brackish water, human-induced changes such as pollution or sewer drainage could cause a huge negative impact on E. caeruleum abundance.

Life History

Darters have a wide range of life histories; however it has been seen that size correlates with most life history characteristics. For example, larger darters grow faster, live longer, produce bigger clutches, and have longer reproductive spans (Paine 1990). Furthermore, it is assumed that mate selection by female darters is common (Fuller 2003). When examining the rainbow darter, Etheostoma caeruleum, life history traits were as follows: average size 45 mm, growth 32 mm, maximum age 4 years, and clutch size 82 (Paine 1990). E. caeruleum mates during the spring, typically when water temperature is between 17-18°C, and they will leave their normal microhabitat in the rapids to congregate on pebbles where the stream leaves a pool to mate (Kuehne and Barbour 1983). Once mates are selected, the fish mate repeatedly for several days until the female lays about 800 eggs (Kuehne and Barbour 1983).E. caeruleum also displays group spawning and the males tend to exhibit territorial behavior during breeding season (Fuller 2003).

Current Management

Currently, the largest threat to Etheostoma caeruleum is run-off and pollution due to urbanization. For instance, one study found that the development of an interstate negatively affected the abundance of several fish species, including E. caeruleum, because of decreasing quality of water of the nearby creek (Ritzi et al. 2004). Therefore, it is extremely important that we monitor run-off and pollution that drains into our rivers and streams due to the adverse effects that it could have on our fish communities. Currently, management plans consist of reducing nutrient, pesticide, and sediment loadings within such streams (Smiley et al. 2009). Furthermore, this same study suggests that conservation practices should be a combination of both physical habitat monitoring and water chemistry monitoring because it would benefit fish communities within headwater streams more than just implementing one conservation practice or the other (Smiley et al. 2009). Although there are broad management plans in place for many rivers and streams and their fish communities as a whole, there are not currently any management plans in place specifically designed for Etheostoma caeruleum. The lack of protection is probably because Etheostoma caeruleum is one of the most abundant darter species. However, although the rainbow darter may be abundant now, many other darter species have become endangered or extinct and therefore, we should implement a better management plan for Etheostoma caeruleum.

Management Recommendations

Etheostoma caeruleum does not currently have any management plans in place designed specifically for it, and due to its sensitivity to water purity and to the fact that it is a primary food source for many larger freshwater fish, it would suffice to say that a better management plan is in need in order to help maintain healthy freshwater ecosystems that it occupies. In order to monitor and manage E. caeruleum, it would be ideal to have a good estimate of the species abundance. To do so, one would need to use seines to catch E. caeruleum and count the numbers of species present in known streams and rivers that it occupies and repeat this process several times a year; doing so would provide a good estimate for average E. caeruleum species abundance. Once an estimate for E. caeruleum abundance is determined, monitoring the annual number of species would show influxes in the abundance of rainbow darters or a decline in the abundance of rainbow darters compared to its average abundance. Management plans should include monitoring watershed from nearby urban areas (i.e. monitoring chemical run-off from agriculture or plants) and monitoring overfishing (since rainbow darters are a primary source of prey for many larger freshwater fish, it is important to keep the balance). Invasive species could also potentially pose a threat to the rainbow darter, and if they were to upset the balance of the freshwater ecosystem, measures would need to be made in order to remove such species.