When a Dead End
Becomes a Path Forward

How Baltimore scientists are re-routing reproduction
to produce sterile fish

Yonathan Zohar. Photograph, Rona Kobell
Yonathan Zohar, who focuses on marine and aquaculture biotechnology, feeds fish in IMET‘s aquaculture center. Chair of marine biotechnology for the University of Maryland, Baltimore County (UMBC), he spends time when he can with the fish. Photograph, Rona Kobell

Two environmental problems are eating away at aquaculture's promise around the world.

The first is genetic pollution. In the Pacific Northwest and elsewhere, aquaculturists have bred domesticated fish that have occasionally escaped from confinement. That could lead to farmed fish displacing wild stocks, or even to Atlantic salmon propagating in the Pacific, where it is non-native, all of which disrupt the ecosystem and food chain.

The second is that fish generate waste, which is often released into the coastal environment. There, it can have an adverse impact on the ecosystem.

At the University of Maryland's Institute of Marine and Environmental Technology (IMET), researchers are developing solutions to both of these problems. If scaled up, the researchers say, their innovations could change the way we grow fish, manage waste, and maintain wild stocks. Those fixes are already happening in countries like Norway, a world leader in aquaculture production, which have invested heavily not just in aquaculture but in the IMET scientists.

Yonathan Zohar, Keiko Saito, and Kevin Sowers on a boat in Norway. Photo courtesy of IMET
Yonathan Zohar, Keiko Saito, and Kevin Sowers on a boat in Norway. They are en route to the salmon farms they are working with on technology to turn fish waste into energy. Photo Courtesy of IMET

First, we look at the escape problem — a serious issue because a fish such as the domesticated Atlantic salmon (Salmo salar), selectively bred to be different from wild stocks, can survive outside confinement and change the genetic composition in the environment. At IMET, scientists Ten-Tsao Wong and Yonathan Zohar have found a way to produce reproductively sterile fish.

In their labs, they have developed a technology that can disrupt the early formation of cells that would otherwise develop into eggs and sperm in a fish. In doing so, they could produce sterile fish. Think of their solution this way: Stem cells on their way to where they will develop into sperm or eggs take a wrong turn and die. To make that happen, they have to silence a protein appropriately called dead end.

The team tested its concept on zebrafish (Danio rerio), which share many genetic and physiological similarities with larger fish.

Zohar, chair of the Department of Marine Biotechnology at UMBC, located at IMET, believes it has "huge potential" for the industry. Wong and Zohar are now working to test the concept on several major aquaculture species, such as Atlantic salmon, rainbow trout, sablefish, and tilapia.

This innovation has major implications, financially and environmentally. Last year, more than 100,000 Atlantic salmon escaped into the Puget Sound. And though the company responsible, Cooke Aquaculture, said it doesn't expect any of the fish to survive and reproduce, an environmental group is suing the company in part over the risks due to genetic pollution of introducing a new species to the Pacific Ocean. If they were bred to be sterile, Zohar said, the risk of them possibly breeding in the Pacific would be far less — though he added that doesn't address the question of why we are raising Atlantic salmon in floating net pens in the Pacific, with the inherent risk of fish escaping.


"We had never seen such a big operation incorporating this kind of technology. . . . It will accelerate the whole aquaculture industry."


Then, the waste: Building on the fully contained aquaculture operation in the basement of the Columbus Center — home to IMET — Zohar initiated a project where fellow IMET scientists Kevin Sowers and Keiko Saito are working on a technology, sponsored by a Norwegian company, to use micro-organisms known as methanogens to break down fish waste. These tiny microbes flourish in conditions with little or no oxygen and produce methane gas as they digest the waste.

Using these beneficial microbes as their workhorses, the team built a system to collect wastewater from fish tanks, concentrate the solid waste in an airtight container, and then let the microbes do the work of converting the waste to methane gas. The biogas produced, much like the natural gas used in homes for heating and electricity, can then either be used as an energy source for the facility where the fish are raised or be sold to an electric company.

In Norway, where aquaculture is an $8 billion industry second only to oil, private companies are turning to Zohar and other scientists for solutions. They cannot continue to discharge the salmon waste produced by land-based hatcheries and nurseries into the fjords, according to stricter government rules, and will eventually have to collect and treat the waste produced by floating net pens too.

The IMET team tinkered in labs overlooking Baltimore's Inner Harbor until they found the right microbial mix. "This is the test case," Sowers said of the methanogen conversion apparatus he and his colleagues keep in the basement of IMET. He and Saito just returned from Norway where they helped launch a waste-to-energy system, based on the IMET technology, at one of the country's largest land-based salmon aquaculture operations.

"We had never seen such a big operation incorporating this kind of technology," Saito said. "It will be a great demonstration project. It will accelerate the whole aquaculture industry."

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