Darters represent a diverse group of fishes within order Perciformes and family Percidae (Simon 2006). Genus Crystallaria, which contains the Crystal Darter, also represents the sister taxon to Ammocrypta (Simon et al. 1992). Crystallaria was originally thought to be a monotypic genus, but contemporary research has led to the discovery that a second species also exists within the genus (Morrison et al. 2006). This species, Crystallaria cincotta, was recently described as a separate species based on genetic data (Morrison et al. 2006). This distinct species is known from a single population in the lower Elk River of West Virginia and represents the only known extant population from the Ohio River drainage (Morrison et al. 2006). The new species is reportedly quite rare and differs from C. asprella via reduced cheek scale rows, a falcate margin on the pelvic fins, a preorbital blotch, and a wider mouth gape (Welsh & Wood 2008).

  Food:  

The Crystal Darter’s diet consists largely of immature aquatic insects including blackflies, midges, and caddisflies (Roberts et al. 2007). Recent research suggests that the alteration of the river ecosystems that this species inhabits has induced changes to its diet (Roberts et al. 2007). The construction of the Tennessee-Tombigbee Waterway in Mississippi, for example, has fragmented the Crystal Darter population into the remaining tributaries (Roberts et al. 2007). As a result, the contemporary diet of the Crystal Darter in this region was found to differ significantly from its historical diet in that taxa more suited to low flow, depositional conditions such as caenid mayflies and daphnid zooplankton have become more favored as prey (Roberts et al. 2007).

Reproduction: The spawning season of the Crystal Darter reportedly occurs from January through mid-April with the possibility of multiple spawning (George et al. 1996). Most females are sexually mature by the time they reach 50 mm in length, with males not becoming mature until 61 mm in length (George et al. 1996). Males begin developing tubercules as early as October, with their anal and soft dorsal fins becoming notably enlarged (George et al. 1996). Reproduction in the Crystal Darter occurs when the female submerges herself in the gravel substrate before depositing her eggs, each containing a small yolk sac with translucent yellow yolk inside, typically in a riffle with a moderate to swift current (Simon et al. 1992). The spawning period tends to be short, only about a week in duration (Simon et al. 1992). After spawning, adults relocate to deeper river channels (Simon et al. 1992). Upon hatching, Crystal Darter larvae are relatively large and possess well-developed jaws and moderately sized pectoral fins (Simon et al. 1992).

  Other Interesting Facts:  

The Crystal Darter is known for its unusual behavior in which it buries itself in the substrate with only its eyes protruding (Daniels 1989). There have been several explanations proposed for this behavior, such as its possible use for ambush feeding, predator avoidance, or energy conservation (Kuehne & Barbour 1983; Williams 1975). However, more recent research on a similar species of darter, Ammocrypta pellucida, supports the theory that the main reason for the burying behavior is to stabilize the individual’s immediate environment in response to the current velocity and turbulence in the water (Daniels 1989).

While not listed by the U.S. Fish & Wildlife Service, the International Union for Conservation of Nature has designated the Crystal Darter as vulnerable due to its decline in habitat area and quality as well as its decreased occurrence (NatureServe 2013). The American Fisheries Society’s Endangered Species Committee has also listed this species as vulnerable because of destruction, modification, or reduction to its habitat or range (Jelks et al. 2008). In Minnesota specifically, the Crystal Darter is considered endangered (Minnesota DNR 2019). Because this species thrives in clear rivers with swift currents, human activities such as channelization, dredging, impoundments, and damming have significantly reduced its amount of suitable habitat while also isolating its populations (Minnesota DNR 2019). Conservation efforts have been made to attempt to protect the remaining viable habitats of the Crystal Darter, with the designation of the St. Croix National Scenic Riverway between Minnesota and Wisconsin serving to protect a portion of the Crystal Darter’s mainstream habitats (Minnesota DNR 2019). Furthermore, Minnesota’s Clean Water Legacy Program is projected to benefit Crystal Darter river habitats by way of sediment load reductions (Minnesota DNR 2019).

Daniels, R.A. 1989. Significance of burying in Ammocrypta pellucida. Copeia 1989: 29-34.

George, S.G., Slack, W.T., Douglas, N.H. 1996. Demography, Habitat, Reproduction, and Sexual Dimorphism of the Crystal Darter, Crystallaria asprella (Jordan), from South-Central Arkansas. Copeia 1996(1): 68-78.

Gilbert, C.R., Williams, J.D. 2002. National Audubon Society Field Guide to Fishes: North America. Alfred A. Knopf, New York.

Hipes, D., Jackson, D.R., NeSmith, K., Printiss, D., Brandt, K. 2001. Field Guide to the Rare Animals of Florida. University Press of Florida, Gainesville.

Jelks, H.L., Walsh, S.J., Burkhead, N.M., Contreras-Balderas, S., Díaz-Pardo, E., Hendrickson, D.A., Lyons, J., Mandrak, N.E., McCormick, F., Nelson, J.S., Platania, S.P., Porter, B.A., Renaud, C.B., Schmitter-Soto, J.J., Taylor, E.B., Warren, M.L. 2008. Conservation status of imperiled North American freshwater and diadromous fishes. Fisheries 33(8): 372-407.

Kuehne, R.A., Barbour, R.W. 1983. The American darters. University of Kentucky Press, Lexington.

Minnesota DNR 2019. Crystallaria asprella. Retrieved from https://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=AFCQC01010.

Morrison, C.L., Lemarié, D.P., Wood, R.M., King, T.L. 2006. Phylogeographic analyses suggest multiple lineages of Crystallaria asprella (Percidae: Etheostominae). Conservation Genetics 7(1): 129-147.

NatureServe 2013. Crystal Darter: Crystallaria asprella. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/5786/15361807

Ray, J.M. 2010. First record of the crystal darter (Crystallaria asprella) from Big River, Missouri, since 1963. Transactions of the Missouri Academy of Science 44/45(2010/2011): 41-43.

Roberts, M.E., Schwedler, C.S., Taylor, C.M. 2007. Dietary shifts in the crystal darter (Crystallaria asprella) after large-scale river fragmentation. Ecology of Freshwater Fish 16(2): 250-256.

Schmidt, K. (1995, March 10). The distribution and sampling gear vulnerability of the Crystal darter (Crystallaria asprella) in Minnesota. North American Native Fishes Association. Retrieved from https://files.dnr.state.mn.us/eco/nongame/projects/consgrant_reports/1995/1995_schmidt.pdf

Simon, T.P., Tyberghein, E.J., Scheidegger, K.J., Johnston, C.E. 1992. Descriptions of protolarvae of the sand darters (Percidae: Ammocrypta and Crystallaria) with comments on systematic relationships. Ichthyological Exploration of Freshwaters 3(4): 347-358.

Simon, T.P. 2006. “Genus Crystallaria (Jordan).” In: Reproductive Biology and Early Life History of Fishes in the Ohio River Drainage, Volume 4: Percidae - Perch, Pikeperch, and Darters, 51-57. CRC Press, Boca Raton.

Stewart, J.G., Barko, V.A., Henry, D.B., Herzog, D.P., Ridings, J.W. 2005. New Records of the Crystal Darter (Crystallaria asprella) in the Middle Mississippi River. The American Midland Naturalist 154(2): 471-473.

Welsh, S.A., Wood, R.M. 2008. Cystallaria cincotta, a new species of darter (Teleostei: Percidae) from the Elk River of the Ohio River Drainage, West Virginia. Zootaxa 1680: 62-68.

Williams, J.D. 1975. Systematics of the percid fishes of the subgenus Ammocrypta, genus Ammocrypta, with descriptions of two new species. Bulletin of the Alabama Museum of Natural History 1: 1-56.