The Little River in Blount County boasts perhaps the best recreation of any waterway in East Tennessee. On any given summer weekend, its banks and currents are littered with hikers, swimmers, fly fishermen, tubers and photographers.

These outdoors enthusiasts come for a taste of the wild, but few are aware of the rare treasure that swims around their feet. This river is the home of the marbled darter (Etheostoma marmorpinnum), an animal found nowhere else in the world.

The marbled darter is a fish closely related to perch and walleye. It is small, seldom breaking three inches in length, and its coloration closely matches that of the creek bed, so it is easy to understand why it may get overlooked.

Today, this little fish is in trouble. Agricultural practices and other human activities over the last hundred years have altered the dynamics of the river. Silt, mud and deep pools have replaced gravel, slab rock and riffles — things that the marbled darter requires to spawn. Toxins from road runoff and dams supplement these issues. Left to its own means, this rare fish would likely diminish into extinction.

Enter Pat Rakes and J.R. Shute, graduates of UT and true fish fanatics. They founded the Knoxville-based Conservation Fisheries, Inc. (CFI), a nonprofit organization dedicated to the preservation of aquatic biodiversity. Within the walls of their modest cinderblock building is a sizeable fish hatchery operation focused on the propagation and reintroduction of rare fishes, including the marbled darter.

The process of rearing marbled darters is difficult.

"They're low fecundity, meaning they produce very little eggs at a time," Shute said. "Because of that it's very difficult to get large numbers of them for reintroduction."

To combat these difficulties, CFI developed two methods of propagating marbled darters. The first consists of traveling to the Little River to collect adults for captive breeding. The adults are gingerly transported to CFI's hatchery facility via tough plastic bags placed inside coolers. Upon arrival, they are acclimated into a vast network of carefully maintained aquaria. With luck, and if the scientists and technicians at CFI are able to accurately mimic the conditions of their home waters, the marbled darters will spawn.

The second way they propagate marbled darters is through collection of the fish's nests. This begins with the CFI team donning wetsuits, masks and snorkels before lifting flat rocks situated atop cavities — the preferred nesting habitat for marbled darters. If nests are found, the eggs will be taken to CFI where they will hatch and grow until they reach their juvenile stage. Shute noted that because of difficulties in captive breeding from a genetic standpoint and because they're available, it's better to collect nests from the wild.

During spawning season at the hatchery, eggs are collected several times a week by hatchery technicians. The eggs are then moved to special trays where they hatch and absorb their yolk sac within their first week of life. For the next few months, the young marbled darters are fed twice daily and given ample space — encouragement to grow rapidly just as they would in the wild. When the fish reach their juvenile stage, they are tagged with a substance that resembles a tattoo. This allows the CFI team to return to the river in the future and see if their fish are surviving and reproducing.

Over the last two years, CFI has successfully reintroduced upwards of 600 individuals back into the Little River. Had they not been given this boost towards adulthood, most of the fish would likely have died and never had the opportunity to reproduce. Development and agricultural pressures on the Little River do not seem to be letting up, however, meaning the work of CFI must go on.

The way Rakes sees it, any endangered species is an integral part of the ecology, and without them our ecosystems could crash.

"We like to get on a plane in order to get somewhere quickly," Rakes said. "If one or two bolts fall out it we may not notice ... it may not mean anything. But at some point, a critical one will fall out and the result will be a plane crash."

He added, "They are our canaries in the coal mine; they are our canaries in the stream."