Every winter in the heart of Dalton, Georgia, a tiny, federally threatened fish embarks on an upstream odyssey that makes the migratory feats of the Atlantic Salmon seem like a stroll through the park. This year, biologists with the Tennessee Aquarium Conservation Institute are using a novel research method as part of a study that will help scientists better understand and protect this minuscule Magellan.
A Trispot Darter (Etheostoma trisella)
The Trispot Darter (Etheostoma trisella) is an elusive freshwater darter that grows no larger than 1.5 inches long. They’re strikingly beautiful fish with three black dorsal saddles, a pale belly and a dark line below their eye. During spawning season, however, male Trispot Darters kick it up a notch, developing intense red-orange and turquoise markings in a bid to attract a mate.
Ranging across Tennessee, Georgia and Alabama in the Coosa River drainage, populations of this little fish have been fragmented by the construction of culverts, dams and reservoirs. These navigational impediments cause more trouble for Trispots than for some other fishes because of their unique life cycle.
“What really makes this fish amazing is that it does not lay its eggs in the river or creek where it lives most of the year like all the other fishes,” says Aquatic Conservation Biologist Dr. Bernie Kuhajda. “It migrates out of the creek, it sniffs and tastes and feels for groundwater, and when it finds it, it swims up these little seeps into a temporary wetland.”
That might be a flooded forest, a pine plantation or even a cow pasture. Once the Trispots arrive in these short-lived habitats, they lay their eggs among the submerged vegetation, sticks and leaves. Since these bodies of water exist only during the wet winter season, Trispot eggs are safe from predators that dwell in areas with permanent flow.
It may not look like much, but this temporary wetland is prime Trispot Darter spawning habitat.
Unfortunately, that remarkable adaptation is also partly responsible for the Trispot Darter’s current conservation predicament. Since its spawning habitat is dry nine months out of the year, well-meaning humans might plow or pave over these temporary wetland sites or put up barriers between the wetland and the creek without realizing it would prevent the darters from traveling up the seeps and into these pools.
Scientists have used traditional methods, such as backpack electrofishing and seining, to identify Trispot Darter habitats, but those techniques can be time-consuming, which reduces the efficacy and potential range researchers can reasonably sample. To hasten the search, the Conservation Institute is working with the Georgia Department of Natural Resources to take advantage of this fish’s winter spawning habits.
Paddling in canoes and equipped with an environmental DNA (eDNA) sampling machine, conservation scientists have been traveling down a four-mile stretch of Mill Creek in Dalton looking for any water entering the main stream from a tributary. In some cases, they find barely more than a trickle, but no matter how small, they take a water sample from that tributary and run it through a fine filter in the eDNA machine.
Field Technicians Riley Widdifield, Alonso Angel Gonzales and Cristian Hernandez, from left, use an eDNA machine to sample a seep running into Mill Creek after accessing the area by canoe.
Those filters are sent to a lab at Mississippi State University, where technicians examine them for evidence of Trispot Darter DNA, which would indicate the species’ presence upstream. If they find it, that might mean the source of that water is being used as a Trispot Darter spawning site. Using this method, conservation scientists can sample more than a dozen tributaries of a river or creek in a single day instead of just one or two.
A creek in the heart of Dalton named after the city’s sprawling carpet industry might seem like an unlikely place to find such a rare fish, but Trispot Darters were collected in a wetland off of a seep that runs across a walking trail along Mill Creek just four or five years ago.
Since that discovery, the dirt trail was replaced with a concrete path, and culverts were installed where the seeps once flowed. Kuhajda feared these alterations might have cut off the darters from their spawning grounds. Fortunately, these tiny fish can swim, splash and leap upstream with remarkable agility.
“Salmon got nothing on Trispot Darters,” Kuhajda jokes as he points out the flow of a seep tangled with decaying leaves, snagging branches and riprap rocks leading to a culvert that the fish have to navigate to reach their spawning grounds. “It’s amazing how they get up there.”
Even those spawning grounds look like little more than a wet ditch or a flooded forest to the unknowing observer. Some sections are just a few inches of waterflowing across tangles of grass and leaves, but the darters are there.
If the eDNA sampling signals that Trispot Darters may be present in a tributary, the scientists will return to more traditional sampling methods for confirmation, a process known as “ground truthing.” Those methods include seine nets or backpack electrofishers, which deliver a mild electric current that briefly immobilizes – but doesn’t harm – the fish and allows scientists to collect and measure them before releasing them back into the stream.
Scientists use a backpack electrofisher to search for Trispot Darters.
Should the study identify any previously unknown Trispot Darter habitats, scientists can begin taking steps to protect the fish in those new locations. That might include replacing poorly-designed culverts that restrict the passage of fish upstream with alternatives that are more friendly to aquatic life.
On a recent outing, the team collected four Trispots: two males — one so colorful that Kuhajda described him as the “Brad Pitt of Trispot Darters” — and two females swollen with eggs (aka “gravid”). As part of their research, the scientists measured each fish and took harmless clippings from their fins before returning them to their homes. DNA from the fin clippings will be used to estimate genetic diversity, which can indicate a population’s resilience to environmental changes such as drought, floods or disease.
The seemingly unlikely location of these federally threatened fish makes the research all the more meaningful, says Recovery Biologist Abbey Holsopple.
Left: Recovery Biologist Abbey Holsopple holds up the "Brad Pitt of Trispot Darters." Right: A passerby photographs a Trispot Darter in a viewing aquarium.
“One of the coolest things about this project is we’re doing it on a stream that is in an urban center,” Holsopple says. “Every time we’ve been out there, we’ve run into a member of the public walking on the parkway who wants to know what we’re doing.”
Those chance encounters lead to a show-and-tell about a fish that few people – even fish biologists – have ever seen.
“We get to show it to people who live in the community so they can have a closer connection to it,” Holsopple says.
