The Pacific lingcod is an ill-tempered, omnivorous fish with a mouth like a messy silverware drawer, its 500-plus teeth arranged haphazardly on two sets of highly mobile jaws. New research, published this month in the scientific journal Proceedings of the Royal Society B, reveals that the Pacific lingcod gains and loses an average of 20 teeth every day.
If humans had the same dental scheme, we’d replace a tooth daily. “Kind of makes braces useless,” says Adam Summers, professor of biology at the University of Washington and co-author of the study. “And brushing.”
The Pacific lingcod’s rate of tooth replacement came as a surprise to researchers, says study co-author Karly Cohen, a PhD student at the University of Washington studying the biomechanics of feeding.
“The existing research we have on tooth replacement comes from oddballs,” Cohen says, such as anglerfish that grow teeth on their foreheads, or the piranha, which can lose a quarter of its teeth at a time. “But most fish have teeth like lingcod. And so it could very well be that most fishes are losing mass amounts of their teeth daily” and replacing them quickly, like this species, she adds.
An ambush predator with teeth to spare
The Pacific lingcod is an ornery sportfish about four feet long at adulthood, an ambush predator that frequently indulges in cannibalism. It’s found on the North American west coast, from Alaska to Baja California, Mexico, and it’s economically important to fishers in part because it’s “great in a taco,” Cohen says.
They’re not a charming fish. “I always joke that lingcod and I never got along,” says Emily Carr, an undergraduate student at the University of South Florida and the study’s lead author. “We had to add tape to the corners of the tanks because when they saw someone walking by, they would try to jump out…I never got bit, but I’m sure they would’ve tried, given the chance.”
A voracious hunter, the lingcod eats “anything it can shove in its mouth,” Cohen says—and there’s a lot going on in its mouth.
“The lingcod have a set of upper and lower jaws, just like ours, but they’re more mobile—they can be thrown forward and spread out,” she explains. “If you look inside the mouth on their palate, it’s also covered in teeth.” Then, all the way at the back of the throat, right before their esophagus, there are the pharyngeal jaws, tooth-studded bony platforms made out of modified gill arches.
When the lingcod attacks, its first set of jaws shoot forward, and drags prey into the mouth where the inner pharyngeal jaws get to work crushing and shredding. For this strategy to succeed, the lingcod relies on needle-sharp teeth, which are prone to breakage. But how to keep its bite from going dull? The strategy seems to be: Constantly grow new teeth. Lots of them.
A toothy fate
In the study, researchers used a sequence of dyes to create a visual timeline of tooth growth.
First, 20 juvenile lingcod were immersed in tanks spiked with the fluorescent dye alizarin red for 12 hours. Since alizarin red is attracted to the calcium in teeth, the result was hundreds of glowing-red gnashers. Over the next 10 days, batches of the lingcod were exposed to a second, green dye, calcein fluorescein. Teeth in place on day one of the study were stained red, while teeth that erupted later appeared green.
Carr painstakingly counted and classified each Christmas-colored tooth—for a grand total of 10,580 teeth in the 20 fish examined.
After examining the smiles of each of the 20 fish, Carr and her team learned that lingcod teeth are fated, meaning each tooth erupts exactly where it’s destined to spend the rest of its career. That’s contrary to other famously toothy fish like the great white shark, whose teeth start out tiny at the back of the jaw and move forward as they grow.
The researchers also identified hotspots for tooth replacement. “It’s not that the really big teeth stay there longer, or really small teeth are constantly replaced,” Cohen explained. “We find that there’s faster replacement in those areas where we expect there to be greater force” when the lingcod chomps down. (Learn more: How some fish—'tiny tanks of the Amazon'—survive piranha bites.)
But what triggers tooth replacement in lingcod? A second experimental condition in the study compared fish that were regularly fed with another group of fish that were given nothing to eat. The researchers found no significant difference in the rate of tooth replacement between them. That suggests the lingcod doesn’t sprout teeth in response to breakage—it may be more like our own baby and adult teeth, which fall out and erupt based on a genetic timer.
Carr says she found the lingcod’s rate of replacement surprising. “There’s this idea that teeth are very expensive to make and replace, but our study challenges this concept,” Carr says. In the calcium-rich waters of the ocean, it’s clearly a worthwhile investment for the lingcod to churn through teeth to keep them sharp.
Oddballs and lingcod
This tooth-growing pattern is an unusual one in the world of fish research—but probably not in nature. The lingcod’s battery of teeth is very similar to those of other bony fish, in number, diversity, and their cone-like shape. That makes it a great model for many different species from a variety of lineages, and the sequential staining of teeth “really quantifies this in a beautiful way,” said Marc André Meyers, a professor of materials science and engineering at the University of California, San Diego, who studies biomaterials, including fish teeth.
Willy Bemis is a professor of ecology and evolutionary biology at Cornell University who researches the anatomy of fish, including the development of teeth. Bemis, who was also not involved in the study, said the experiment’s design was innovative and helps answer long-held questions about tooth replacement in relatively normal fish like the lingcod.
Historically, the rate of tooth growth and loss in fish has been hard to estimate—“for example, for sharks, the best data come from studies that collected and counted lost teeth found on the bottom of holding tanks,” Bemis said. And since sharks have been observed snacking on their own fallen teeth (perhaps to recoup their calcium investment), that data has always been a little suspect.
That makes the lingcod study “important work” since it demonstrates a technique that can be replicated with other species, Bemis explains. Meyers adds he’d be interested in conducting a similar study with piranha.
The results suggest teeth might not be as irreplaceable or precious as we thought. Just don’t tell the tooth fairy.