One mussel, two mussel, red mussel, blue mussel

Staff at a fish hatchery in West Virginia are developing a new technique to help biologists tag freshwater mussels with food coloring.

At White Sulphur Springs National Fish Hatchery in West Virginia, biologists raise tens of thousands of freshwater mussels every year. The mussels that grow up in this facility are released into the wild to give native populations a much-needed boost: 70 percent of North American freshwater mussel species are in decline.

But keeping track of that many animals is a big job, which currently requires staff to mark each individual mussel with a unique identification tag. It’s a time-consuming task that slows down mussel production. To speed things up, hatchery staff are experimenting with a new tagging method that will make it possible to raise and release even more freshwater mussels.

Like so many good experiments, the inspiration for the idea came from the grocery store baking aisle.

Motivation for mussel production

Multiple mussels of varying sizes that appear a tannish-yellow color.
Hatchery-raised pistolgrip mussels (Tritogonia verrucose). USFWS

Declines in freshwater mussel populations are bad for other aquatic organisms too — and for us. Mussels are crucial for maintaining water quality and reducing erosion and sediment transport in streams. That’s where hatcheries can help: by supplementing native mussel populations with hatchery raised mussels, they make up for losses in natural systems.

Raising mussels in a hatchery is a complex undertaking. Rearing different species of healthy mussels in large quantities requires a lot of time, equipment, and resources. Not to mention, patience: tagging each individual mussel to ensure it can be correctly identified in the wild is a tedious process.

There are two standard methods for tagging mussel shells: either supergluing tiny plastic ID tags, or laser engraving a unique ID. Each is time consuming and expensive.

A blue net filled with brown striped mussels, each displaying a small yellow ID tag
Mussels with superglued ID tags on the shells. Rachel Mair/USFWS

The biologists at White Sulfur Springs were looking for a way to make the process more efficient to help them scale up. They started thinking about ways they could “batch mark” the mussels, tagging large numbers of them all at once.

Biological technician John Moore had an outside of the box idea, inside the pantry: food coloring! Yup, the very same thing you might use to make purple frosting or dye an egg.

What’s in a shell

Four petri dishes each displaying a different color of dozens of tiny mussels.
Wavy-rayed lampmussels after twenty weeks in dye. Starting from top left, clockwise: red dye, blue dye, control, purple dye. USFWS.

Dying mussels like Easter eggs seems like a pretty simple solution, but because it had never been done to scale, there were many unknowns. So, the hatchery began an official research study: batch tagging mussels with non-toxic food coloring. “The goal was to come up with a different way of tagging the mussels that’s not as labor intensive when you are dealing with forty thousand animals,” Moore said.

They began applying dye to three species of mussel: fat muckets, pistolgrip mussels, and wavy-rayed lampmussel.

The biggest concern going into the experiment was how long the mussels would retain the colored dye. If the color washed away within a few days or weeks, the idea would be a bust. The coloring would need to last months in the hatchery, and years in the wild.

But initially, the coloring didn’t seem to last at all.

“After we added red for about two months, and nothing happened, we gave up,” said Andrew Phipps, biologist at the West Virginia hatchery. The viability of the new technique seemed doubtful.

Two weeks later after they gave up hope, Moore noticed something that revived it: a red line had appeared in the shell of a mussel. To his amazement the mussel was actually taking in the dye and incorporating it into the pigment of the shell. “The dye wasn’t just staining the shell. It was growing into it,” he explained.

a mussel with red coloring along its outer edge.
A young wavy-rayed lampmussel after exposure to red dye. USFWS.

It turns out the animals filter the dye when they filter water. They obtain nutrients from their water source, so with food coloring added in, they were incorporating both the nutrients and the dye into their shells as they grew.

Most importantly there appeared to be no negative effects from the dye for health, growth, and survival of the mussels in the lab.

The future is colorful

Although individual tagging will still be necessary in some cases, batch tagging is a helpful method for hatcheries to quickly and easily mark mussels to distinguish and keep track of different species, from different watersheds.

a container holding red, blue, purple and naturally colored mussels.
Wavy-rayed lampmussels after thirty weeks of dye exposure. Some of these mussels were in red dye, others were in purple or blue, and some were from a control group with no dye. USFWS.

It could also make surveying for mussel brood stock in the wild much easier for biologists. They will quickly know if mussels are wild-grown or if they came from a hatchery, and which one.

two people wade in knee deep water using triangular devices to see underwater
Biologists searching for mussels in a stream using viewing buckets. Gary Peeples/USFWS

The biologists are continuing to monitor the mussels at the hatchery to evaluate the long-term retention of the dye in the shells, but the results so far are promising. Once the results are in, biologists may have a new tagging method that could save significant time, money, and most importantly, increase our capacity to stock freshwater mussels in the rivers and streams that need them.

By Colleen Andrews and Bridget Macdonald

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U.S. Fish & Wildlife Service Northeast Region

U.S. Fish & Wildlife Service Northeast Region

Conserving wildlife and habitats from Maine to Virginia, New York, and Pennsylvania.