The Diamond Darter (Crystallaria cincotta) is a rare fish native to the Ohio River drainage with its current population confined to just a single location - a less than 40 kilometer stretch in West Virginia. This species was first formally described in 2008 (Welsh and Wood, 2008), and based on historical museum specimens the Diamond Darter once spanned within the Ohio River drainage, throughout Kentucky, Ohio, and Tennessee. The decline and extirpation of the Diamond Darter is largely attributed to changes in its river habitat. The construction of dams, channel modifications, and siltation have all contributed to the degradation of the river systems that the darter depends on. Fine sediments—often from erosion caused by urban, mining, and rural development—fill the spaces between the gravel and sand where the Diamond Darter lays eggs, hides, and hunts. This disruption of its habitat has led to the species' current critically restricted range.

In recognition of its dwindling population, the U.S. Fish and Wildlife Service (USFWS) listed the Diamond Darter as a candidate for Endangered or Threatened status in November 2009. By 2013, the species was officially listed as Endangered under the U.S. Endangered Species Act, emphasizing the urgency of conservation efforts for this darter.

The Crystal Darter (Crystallaria asprella) has long held a place of scientific interest due to its unique life history and taxonomic journey. Initially placed in the genus Ammocrypta among the sand darters, it was reclassified into Crystallaria by Simons (1991), based on distinct characteristics that warranted this shift. The Crystal Darter was the only species in the Crystallaria genus for many years until the discovery of the Diamond Darter, in 2008.

Although the two species are closely related, there are subtle differences between them, such as the Diamond Darter’s wider mouth gape and reduced cheek scale rows. Despite these differences, their ecological roles and life histories are likely very similar, making the Crystal Darter an invaluable model for studying the Diamond Darter.

From 2010 to 2014, CFI worked extensively on developing propagation protocols for the Diamond Darter. While we successfully produced hundreds of eggs and larvae, we struggled to ensure the survival of the larvae. Close observations revealed a surprising finding—older larvae were consuming younger ones, suggesting that they might be specialized feeders targeting smaller larval species. Additionally, the larvae displayed large, teeth-like structures at 10 days old, hinting at a specialized feeding mechanism.

Despite these challenges, CFI’s work with the closely related Crystal Darter has proven promising. In 2022, CFI successfully developed propagation protocols for the Crystal Darter, and we are optimistic that these insights will help us refine methods for the Diamond Darter.

Sampling for the Diamond Darter in free-flowing rivers has always been a challenge. Their nocturnal nature combined with their ability to bury themselves in the sand makes traditional sampling methods ineffective. For years, researchers struggled to collect sufficient data on this elusive species.

In 2011, during a collection for breeders we made a telling discovery. After two hours of nighttime downstream seining, we took a break to rest. While walking along the riverbank with a spotlight, we spotted something distinctive—a Diamond Darter sitting out in the open, patiently waiting for food to drift by! This was a groundbreaking observation as it had never been noted before that these darters venture out at night in search of food. 

This behavior led to the development of a new sampling technique which we coined "spotlighting". By using a spotlight to locate the darters at night, we could observe them more easily than during daylight hours when their tendency to bury themselves in the sand made them nearly impossible to find, let alone catch.

The success of this method was immediately evident. In 2012, spotlighting allowed USGS to conduct a more extensive survey of the Elk River population. They found more Diamond Darters in a single year than had ever been documented, providing invaluable data for ongoing conservation efforts.

Efforts to restore the Diamond Darter to its historic range are ongoing. By applying the knowledge gained from working with the Crystal Darter, we hope to aid in the recovery of this Endangered species. With focused conservation efforts and a deeper understanding of its life history and reproductive needs, we remain hopeful that the Diamond Darter will once again thrive in the rivers of the Ohio River drainage.