Using their mouths, tiny male fish build elaborate stone structures to attract females
Whitney Pipkin, BayJournal.com
“Nest builder, nest builder, build me a nest,” Eugene Maurakis hummed unselfconsciously, replacing the lyrics of a familiar Fiddler on the Roof tune with his own while arranging river-smoothed rocks into a neat mound on a dry path.
A stone’s throw away, just under the surface of the Rapidan River in Virginia, a male bluehead chub had painstakingly constructed a heap just like this, called a nest, by moving dozens of rocks into place, one at a time, with his jaws. The mouth-made nests serve as spawning grounds and temporary homes to fertilized eggs and tiny larvae — and they are the inspiration for the name of a captivating category of fish species: nest builders.
These fish only exist in Eastern and Central North America and represent just 8% of minnows in the region. Out of 19 species of nest builders, seven live in the Chesapeake Bay watershed, dispersed among rock-bottomed streams connecting to rivers like the Rappahannock, James, Potomac, and Susquehanna. Most of the nest builders are small, with males typically maxing out at 6–8 inches in length.
Virginia, with the land that drains to both the Chesapeake and the Tennessee River, is home to nine nest-building species in all. The state has been the site for more than three decades of research by Maurakis, a professor at the University of Richmond and a retired chief scientist from the Science Museum of Virginia who can replicate each genus’ intricate nest from blueprints in his mind.
His work will culminate in a documentary slated for release next year, a collaboration with the film and art departments from other universities.
“The only place these fish appear on Earth is right here in this part of America,” Maurakis said. “When you think of it, there’re 31,000 fish species and counting on Earth — and there’s just a handful that does this.”
All members of the Cyprinidae family of fish, these nest-builders include the bluehead chub, bull chub, river chub, creek chub, cutlips minnow, and fallfish. Though there’s some debate over the inclusion of a fish that pushes rather than picks up its rocks, the central stoneroller could also be considered a nest builder.
All of the active nest builders, excluding the stoneroller, have keratin — the protein that forms fingernails — on the inside of their mouths. The females and immature males do not build nests, so they do not have keratin, and the stoneroller has keratin on the outside of its chin and lower jaw instead.
“We hypothesize that it serves as protection, almost like a callus,” Maurakis said.
Unlike the freshwater species with which most fishermen are familiar — such as the trout that flutter their fins and bodies to shape gravelly nests — these fish function as architects of their nurseries. Depending on the species, the fish can carry stones that range in size from pea-size pebbles to several centimeters across. Some males spend up to 36 hours fussing over their arrangements, sometimes swimming several meters away to gather just the right stone as the females wait and watch nearby.
In the end, the female decides whether to spawn with a male. Her decision could be based on his nest-making abilities, but researchers think is more likely based on his size.
“It’s an interesting irony in terms of gender roles for human beings,” said Scott Putnam, an associate professor in Virginia Commonwealth University’s department of dance and choreography. He is working with Maurakis on the documentary, which will use choreographed routines as well as underwater video to portray the fish’s intricate mating dance.
“We tend to think of pregnant women ‘nesting,’?” he said, but, with these fish, the males are “building a nest to welcome that connection. It’s really quite lovely.”
As romantic as the notion sounds, the fish are not monogamous. Though one male builds the nest, several males and females typically use it for spawning, and some species expand their mounds as they go until they reach up to two meters across.
While the relatively small fish might be hard to distinguish from others, their freshly constructed nests are easy to spot in the clear, shallow waters of a Virginia stream. Though they can be flattened by logs or swimmers, the mounds of rocks stand out for weeks after the spring spawn against an otherwise algae-covered substrate.
Maurakis was thumbing through his field notes, which record the 3,500 miles he’s driven just in Virginia so far this year — between Bath County and Blacksburg — when his wife spotted unexpected movement in a nearby stream.
“You’ve got an active nest down here,” said Penelope, a preschool teacher who sometimes joins her husband on research trips during the summer. “I just saw a fish with a rock in its mouth.”
It was an early July day, weeks after spawning should have wrapped up in an unspoiled stretch of the Middle River in Madison County, but water temperatures had cooled enough to lengthen the season for some newly matured males. Sure enough, a bluehead chub was hovering around a freshly formed pile of rocks.
“Get out!” Maurakis said in disbelief, donning his hip waders and camera to get a better look.
In all, about a dozen nests were clearly visible, even to the untrained eye, from a bridge that crossed the river there. The bluehead chub, orNocomis leptocephalus,is also relatively easy to spot, named for its stocky body and the distinctive hue of its head, which is covered in white tubercles that look like tiny horns — they also are called “horny heads.”
“It blows my mind when we come to a stream and he can identify basically anything that we see,” Penelope said. “Unless they have a giant blue head, I don’t know what it is.”
Maurakis and his collaborators, including Emmanuel Frimpong, an associate professor of fish and wildlife conservation at Virginia Tech University, hope to get more people hooked on these fish that many know so little about. Because most nest builders are no more than 8 inches long, the general public thinks of them as little more than bait.
“People say, ‘Oh, it’s just minnows. I fish for bass,’” Maurakis said. “But we’re hypothesizing that — once they understand that there are these gorgeous, fascinating fish in this stream by this park over there — that they’ll begin to consider changing their behavior.”
When people throw old tires or oil into a backwoods waterway, Maurakis said, they don’t realize that it could impact the entire ecosystem that supports these fish.
Maurakis, who lives in Midlothian, knows firsthand that pollution continues to threaten these fish that thrive in cool, pristine waters. He once found a pool of dead fish in a stream near his house that was later traced to someone draining their chlorine-rich swimming pool into the nearest waterway.
Nest builders, like much other freshwater fish in suburban and rural areas, are sensitive to a suite of pollutants, whether they wash off fertilized lawns or farm fields. More than 700 of the 1,200 species of freshwater fish in North America are considered imperiled by the American Fisheries Society, meaning they are vulnerable to becoming endangered or extinct. Of those, 25% are minnows and chubs, a group that includes nest builders.
After studying these fish for more than 30 years and writing, with colleagues, some 35 peer-reviewed studies about the creatures, Maurakis now wants to better understand what people know about them and what they don’t. A press release announcing a grant Maurakis received from the Virginia Academy of Science to carry out this new phase of research stated that people today are more likely to know about wildlife in Africa than about environments in which they live.
That’s something he’d like to see change, and he thinks the nest builders will make good torchbearers for the cause. After tagging along for a few nest-spotting trips this summer, his wife has become the most recent convert.
“I feel a certain sense of excitement when I go to a stream and see that pile of rocks,” Penelope said. “It kind of gives me hope to see that, with so much pollution going on in some areas, there are still some pristine streams around that are full of life.”