If you’ve ever had a pet goldfish, you know fish produce waste. What to do about this waste in a commercial aquaculture operation can be costly and challenging.
Mike Acquafredda has spent the past 2 years testing the feasibility of integrated multi-trophic aquaculture at our Howard Laboratory in New Jersey. This is an environmentally sustainable way to grow fish. In these systems, two or more species from different links of the food chain—scientists call them “trophic levels”—are grown together. Fish waste and uneaten food are used by the other species in the system to produce more products that the farmer can sell.
The system Mike built and studied included three trophic levels:
- Striped bass, a high market value fish that people like to eat
- Sandworms, sought after for bait; also used to feed farmed fish
- Sea beans, an edible sea vegetable that can also be used for biofuel and animal fodder
He also grew striped bass in a conventional recirculating system for comparison.
Fulfilling A Childhood Dream
Mike grew up in Monmouth County, New Jersey, where our Howard Lab is located.
“Sandy Hook has always been one of my favorite places on the planet,” he shared. “As a child, I would come to the hook and wade in the tide pools, looking for snails and shellfish, and go fishing on the ocean side. I dreamed of one day working at the NOAA lab here.”
Mike earned his bachelor’s degree in biology at Tufts University and his doctorate in ecology and evolution at Rutgers University. As a doctoral student at the Haskin Shellfish Research Lab he studied diversifying the Northeast’s aquaculture sector.
He was awarded a Knauss Marine Policy Fellowship in the final year of his Ph.D. and worked with the NOAA Ocean Acidification Program in Silver Spring, Maryland.
Mike wanted to return to research after his fellowship, so he applied for a postdoctoral research opportunity at the Howard Lab. His first few months were spent scouring the scientific literature and planning his experiment while working from home during the pandemic. This allowed him to hit the ground running when he got into the lab.
Developing the Experiment
Mike came across the concept of integrated multi-trophic aquaculture during his Ph.D. research. “Building farms as these little ecosystems with species that feed from one another is really cool,” he explained.
"My background is in shellfish aquaculture, which generally speaking is already quite sustainable. Unlike shellfish, fish have to be fed. I was excited to work with finfish because I felt that I could make more of an impact by figuring out ways to make finfish aquaculture more sustainable.”
Mike read up on native species that might work in this type of system. He sought input from aquaculture practitioners and other scientists.
Striped bass are one of the most popular aquaculture species in the United States. The striped bass for this experiment came from the Pamlico Aquaculture Field Laboratory at North Carolina State University. They weighed less than 1 ounce each at arrival and grew to about 1 pound within a year.
Mike chose to grow sandworms because research suggested they could survive solely on fish waste. The worms for his experiment were harvested in Maine, where there is a lucrative but declining sandworm fishery.
He chose Salicornia bigelovii, also called "sea beans" or pickleweed, for the bottom trophic level because it has the highest salt tolerance of any edible native marsh plant. There is an emerging market for it, particularly at high-end restaurants and grocery stores. The seeds for this experiment came from Heron Farms, based in Charleston, South Carolina.
Both sandworms and sea beans can grow by using waste and nutrients from fish farming. While scavenging sandworms eat the solid waste, sea beans use waste in the form of nutrients dissolved in seawater.
Is integrated multi-trophic aquaculture feasible?
The experiment ran for about 5 months, from late November 2022 to April 2023. Mike harvested the sandworms and sea beans, but has kept some of the striped bass to continue measuring their growth. Howard Lab staff are still processing samples.
Mike confirmed that the striped bass in the integrated multi-trophic system and those he raised in a conventional recirculating system grew at similar rates. This is critical for the system to be viable, because fish are the “cash crop,” the most reliable source of income for the farmer.
Mike explained, “Integrated multi-trophic aquaculture is feasible and can be environmentally sustainable. Whether or not it can be profitable depends on how creative growers can be with developing cost-effective systems.”
The sandworms recycled 45 percent of the fish waste and uneaten food from the system. Mike also harvested more than 54 pounds of sea beans, which recycled dissolved nutrients resulting from waste. He explored culinary uses for it, including “pickled pickleweed,” shrimp and sea bean scampi, and a vegan crab substitute.
By his calculations, with more space they could have produced twice as many worms and four times as many sea vegetables, recycling even more of the fish waste.
Mike explained, “We can produce food in ways that reuse as much of the inputs as possible. This is part of the circular economy.”
Infrastructure and People Made the Experiment Possible
The Howard Lab’s recirculating aquaculture systems allowed Mike to run the integrated multi-trophic aquaculture system and a conventional system at the same time in the same space for an “apples to apples” comparison.
Still, the team ran into challenges running two large and complex systems. “There wasn’t a single week where everything worked perfectly, but I like problem-solving; that’s why I’m a researcher. The nature of working in a marine lab is that things break and you roll with the punches.”
Mike’s favorite part of the project was mentoring students. He mentored Jiyahna Price, an IN FISH summer intern from Bethune-Cookman University in 2022. He mentored two seniors from the Marine Academy of Science & Technology throughout the previous school year.
“It was rewarding to expose young people to aquaculture and the scientific process,” he expressed.
A Future in Aquaculture Science
Mike is excited to return to Haskin Shellfish Research Lab at Rutgers University this fall as an aquaculture specialist. He will use science to solve industry problems and connect aquaculture practitioners and the public with researchers at the university.
“It’s a bittersweet moment. I’ve enjoyed working at the Howard Lab. I’ve gotten attached to my coworkers and my project,” he shared. “But I’m also looking forward to the next chapter and there will be many opportunities to collaborate with NOAA Fisheries in my new role.”
