Scientists gathered around blue buckets filled with water and colorful Pumpkinseed Sunfish inside a humid lab at the historic Fairmount Water Works along the Schuylkill River.
The researchers used turkey basters to vigorously stir the water to help mussel larvae attach to the fish’s gills. After a mother mussel releases her larvae, they must affix to a fish host in order to develop, whether in nature, or in a lab.
Lance Butler, a senior scientist at the Philadelphia Water Department’s Office of Watershed, carried a wriggling fish to a microscope in search of larvae, each smaller than a grain of sand.
“We’ve got attachment. We’re in good shape,” he said to his team, before repeating the routine from bucket to microscope for another 20 minutes.
Known as nature’s Brita filters, freshwater mussels treat up to 300 gallons of water each month. However, populations are in jeopardy, partly because of poor water quality and man-made dams that prevent the movement of fish species mussels rely on to survive.
So, in 2018, the city and five organizations began propagating mussels in a lab to increase populations in the Delaware River Estuary.
This year, the hatchery doubled the number of mussels it typically produces, thanks to scientific discoveries.
Researchers thought Alewife Floaters, a mussel species found in the Delaware River, could only develop through their parasitic relationship with American Shad and River Herring, such as Alewife fish.
So, for years, the team collected the herring from the Blue Marsh Reservoir. However, up to half of the fish died upon being caught, or while in their new lab environment.
Last month, the scientists successfully produced juvenile mussels by helping larvae attach to hybrid striped bass. They found that not only did the fish species better survive in the lab than herring, but it also yielded more juvenile mussels, said Butler.
“We got in one inoculation about 12,000 juveniles off 60 fish. That’s unheard of,” he said. “That’s a great success, and it’s great for the scientific community to know there are alternative host fish for this species.”
Butler believes the hatchery is the first in the nation and possibly the world, to pair Alewife Floaters with striped bass for propagation purposes. The research team does not yet understand the reason for the high yield rate.
A new large-scale commercial hatchery will break ground next year at Bartram’s Garden, allowing researchers to produce about a million mussels per year.
In nature, mussels produce about 50,000 to 150,000 larvae. However, only about 1% eventually turn into adult mussels. After mother mussels release larvae, they must attach themselves to the gills of a host fish within a couple of days. They remain in a cyst on the fish for two to five weeks until they mature into adults and fall to the bottom of the water.
Scientists can increase the mussels’ chances of survival by replicating its life cycle in the lab. The process from propagation to releasing the mussels into rivers lasts about a year and a half.
“I remember the first time that I saw a little baby mussel under the microscope,” said Kathryn McFarland, a Drexel University undergraduate student who works in the hatchery. “Seeing that mussel that’s half the size of a grain of sand, and now to be able to see it double, triple in size just within a few weeks — I’m really looking forward to seeing that kind of full circle process.”
The hatchery’s improved success makes restoration, and improved water quality, more possible, said Matt Gentry, a scientist with the Partnership for the Delaware Estuary. He said he’s gained a greater appreciation for the species since working at the hatchery.
“They’re not charismatic megafauna, they’re not like working with wolves or something like that. But once people … go out for surveys, it feels like a treasure hunt, because there’s these things that you never knew existed,” Gentry said. “You go out with a snorkel and wetsuit, and all of a sudden, you’re seeing them hidden around rocks, and finding a whole world of diversity on a smaller scale that you never really appreciated before.”
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