While some of the largest fish in Tennessee waters are catfish, there is a species of the whiskered fish smaller than a pen cap.
The pygmy madtom is an endangered fish so rare it has only ever been found in Tennessee. Small populations of the fish have been found in the Clinch River in Hancock County and the Duck River in Hickman and Humphreys Counties but nowhere else in the world.
Two graduate students at Tennessee Tech University have put their focus on understanding the fish and developing techniques that could change the way scientists study not only the pygmy madtom but other endangered fishes as well.
“As far as we know, it is the smallest madtom species,” said Tech graduate student Grady Wells who is studying the fish.
The pygmy madtom could grow to be as large as 50 millimeters, but most adults fish are 30-40 millimeters in length.
“So, the biggest one would be like the size of a pen cap, and this is a catfish, with the whiskers and all of those structures,” Wells said. “Unlike the big, forked-tail channel catfish, the pygmy madtom is on a much different scale.”
With the distinct coloration of a dark brown upper portion of the body and a nearly white belly, it is easy to identify the fish, Wells said, but finding specimen is not as simple. The pygmy madtom was federally listed as endangered in 1993 and is one of the smallest and rarest North American fish.
Wells’ research seeks to understand the biology and habitat of this species to form conclusions that could help preserve the population.
“Even at sites where we reliably can find them, sometime it is still hit or miss,” Wells said.
There have only been about 100 of these fish ever recovered and in his field work, Wells has made more than 1,000 seine net efforts and only recovered six of these fish.
“So, they are still a very rare species in regards not only to their population number but in regards to other fishes in the community as well,” Wells said. “It is one of the best moments of your week to see one of those.”
The Clinch and Duck rivers are both large bodies of water, but a technique for finding this small fish in a big river is being developed by another Tech graduate student, Robert Paine.
Paine is working on an approach to habitat identification that looks for environmental DNA (eDNA), things like mucus or scales left behind in the environment, to determine if the rare pygmy madtom is present in a specific location.
“I can scoop up water that hopefully has eDNA in it and get a better estimate whether or not that fish is actually present,” Paine explained. “It is kind of a scouting mission because we are trying to see where in the water and in what type of water, like flowing or slack water, might be better for detecting it.”
Environmental DNA is not necessarily a new concept, but applying the methodology to an animal that is in need of conservation is especially appealing to Paine.
“Tennessee is such a biologically diverse state but there is a lot of overlap in terms of species with other states, so if Robert’s tool works, it is something that out local resource management can potential apply in other states for other fishes and even other organisms for that matter,” Wells said.
The invasive Asian carp is another example of a fish that Paine is using eDNA to find. Since the first fish of an invasive species to make their way into an area are generally few in number and sometimes hard to pinpoint, much like the rare pygmy madtom, if Paine’s environmental DNA approach works, it could be used to help combat that fish’s spread.
“If we can use these tools to detect this rare pygmy madtom, they could be used to detect other fresh water fishes with similar levels of rarity,” said Hayden Mattingly, director of Tennessee Tech’s School of Environmental Studies.
Ultimately, the results of the work Wells and Paine are doing will fill gaps in ecological knowledge of the species, add to the natural history of the fishes of Tennessee and the Southeast. It could also be a guide for conservation efforts of fishes that share the pygmy madtom’s rarity.
This pygmy madtom, measuring 34-mm, was found near Hite Ford on the Duck River.
This female pygmy madtom, measuring 41-mm, was found near Frost Ford on the Clinch River.