How does this fish keep its 500 teeth nice and sharp? Scientists have the answer

Story Transcript

The Pacific lingcod is constantly making new teeth.

The predatory fish have 500 pointy teeth in multiple rows, which they use to latch onto their prey and shred them into digestible bits. 

And in order to make sure their chompers are up to the task, they lose and replace about 20 teeth every day, according to a new study published in Proceedings of the Royal Society B.

"For you and I, that basically looks like losing a tooth every single morning," co-author Karly Cohen, a doctoral candidate at the University of Washington, told As It Happens host Carol Off. 

"Like, we'd wake up and a tooth would be gone and then it would come back. It's nuts."

A summer of counting fish teeth 

The lingcod is a "ferocious looking fish" that can grow up to a metre in length, and weighs about 36 kilograms. It feeds on whatever creatures it can fit inside its mouth, and has jaws powerful enough to break through the shells of armoured crabs and other crustaceans. 

In order to eat its prey, it relies on its rows upon rows of razor sharp teeth.

"We can hold a piece of fruit and bring it to our face and chew down on it. But fish don't have limbs — at least most of them don't — in the way that we have limbs," Cohen said.

"And so having this many teeth helps them not only chew through their food and bite through their food, but hold onto it."

In order to study the toothy beast's dental maintenance, the researchers kept 20 lingcod at the University of Washington's Friday Harbor Laboratories to track how many teeth they lost and regrew on a daily basis.

They placed the fish in a seawater tank with red dye, which stained their teeth, then moved them back into their regular tank for 10 days.

After that, they moved the fish again to a tank with green dye, then euthanized them and examined their mouths to see how many teeth had both red and green colouring.  

"It's a little horrifying when you look on in there and you just see the sea of small, pointy, clear cones," Cohen said.

The team counted more than 10,000 teeth in total. Most of that work fell to Emily Carr, an undergraduate researcher at the University of South Florida and the lead author of the study.

"She really did the bulk of the sitting at the microscope and counting these teeny tiny teeth — which was an excellent way for her to spend her summer, in my opinion," Cohen said.

The researchers found the fish replaced the teeth from its back rows most often. Those are the ones that do most of the chewing, as opposed to the outer rows, which are designed for catching prey.

But the teeth aren't coming out due to wear and tear, Cohen said.

"It's not so much that they're wearing away or breaking away. We tried to induced that in the lingcod by feeding them lots of hard prey, and it didn't seem to change much," she said.

"It seems like maybe somewhere in their own regulation of replacing teeth and their own maintenance, whatever that time cycle is that, they've adapted and evolved this pattern of replacement."

The scientists suspect the fish lose and replace so many teeth so they're always ready to chow down.

"I think it probably has to do with maintaining the ability to have sharp teeth and maintaining having a whole dental battery of really nice, sharp teeth that are ready to go and ready to eat," Cohen said. 

The lingcod is not alone in the fish world when it comes to having lots and lots of teeth.

"It looks like fishes in general replace their teeth all the time throughout their life. The best case example of that is in sharks that are always replacing their teeth," Cohen said.

"I mean, there are rivers in Florida where you can kind of bend down and scoop through the fresh water and you pull up fossils [of] shark teeth."

But while shark teeth are well studied, the same can't be said for most fish.

"This starts to give us a baseline understanding of just how quickly the replacement can happen in these bony fishes, and we can start to ask better questions about what drives the vastness or the speed of this replacement," Cohen said.

Written by Sheena Goodyear. Interview produced by Ashley Fraser.