Fish in the Fields

Fish in the Fields

Fish in the Fields: FLBS Scientist Works with California Conservation Group to Reduce Methane Emissions in Central Valley Rice Fields

by Heather Fraley, Environmental Science and Natural Resource Journalism Intern

Deborah Moskowitz stared at two jars of water from different experimental ponds in a California rice field. Dozens of tiny animals called zooplankton, drifted gently in the brownish water from a control pond that had been left as is. The other jar held water from a pond where golden shiner minnows were stocked. Only a few lonely zooplankton floated in it. Adding fish to flooded rice fields was changing the food web just as Moskowitz had hoped. Fish were eating the zooplankton, leaving methane gas-eating bacteria predator-free, and less methane was escaping from the flooded fields into the atmosphere. It was the first step to decreasing the carbon footprint of the California rice industry, and improving sustainable aquaculture in the Central Valley and beyond.

 “After working on this project for seven years, there were tears,” says Moskowitz as she described how it felt to see the difference between the two jars. “Just the idea that this could work is so exciting.”

Moskowitz is the president of the Resource Renewal Institute (RRI), a California-based nonprofit that innovatively solves environmental problems. RRI is collaborating with scientists at the University of Montana’s Flathead Lake Biological Station and the University of California, Davis on the “Fish in the Fields” project. It started out as a sustainable foods idea. Seven years later it’s grown into a concept with vast potential for climate change solutions and fish conservation.

University of Montana scientist Shawn Devlin who oversees the research, just finished analyzing data from the first winter field season. He describes the preliminary results as “significant and compelling.” They show 70% less methane in the ponds where fish were added. The results, although still early, add scientific weight to the difference in the two jars that Moskowitz noted with the naked eye.

Let’s Put Fish in the Fields

The Fish in the Fields Project was born in a duck blind in the Central Valley. RRI founder and exceptional conservationist Huey D. Johnson went out duck hunting as he did every year. While squinting out from under his tweed cap, he realized that the artificial ponds in the rice fields were only being used by ducks. Why not grow fish in them for people to eat or maybe even for conservation?

RRI got permission from some farmers and started adding fingerling fish to rice fields in 2012 to see if the idea was viable. The tiny fish thrived in the ponds, growing at astonishing rates with no supplemental feeding. Growing the fish was remarkably easy. Marketing them was not. Rice farming is the second-highest producer of methane gas in California behind only the cattle industry. This created a stigma that was hard to get past. Patagonia Provisions loved the sustainable aquaculture idea, but they didn’t want to associate with methane production. It was back to the drawing board for Moskowitz and RRI.

The methane problem

Rice fields create four tons of waste straw per acre. Farmers in the Central Valley used to burn the left-over straw because it was cheap and easy. When California became more populated, people saw the effects of burning on air quality, and it was phased out under the state Rice Straw Burning Reduction Act of 1991.  This created pushback from rice farmers who now had literally tons of straw that they couldn’t get rid of.

Third generation Yuba County rice farmer Charley Matthews Jr.’s family has been farming rice in California since 1912. He remembers when burning ended. “A lot of people at the time said this is the end of the rice industry,” he said. “I was kind of a young one at the time, and I said ‘no this is minor.’ We started flooding our rice fields and incorporating that straw into the soil.” “Pretty soon it became an industry-wide thing, and at the same time we noticed an increase in wildlife.”

Flooding the rice fields in the winter when the fields weren’t in use, allowed the waste straw to decompose. It had the added benefit of putting nutrients back into the soil for the next growing season. On top of that, rice farmers got accolades for creating the artificial square-shaped ponds like giant waffles filled with syrup. They provided important winter habitat for waterfowl in the Pacific flyway. It seemed like the perfect solution. Suddenly rice was the “environmental crop.”

But there are tradeoffs with everything. Decomposing straw in flooded fields also produces a lot more methane, a greenhouse gas. Increased methane production brought new environmental concerns and climate change implications.

Methane is 25 times more potent a greenhouse gas than carbon dioxide over a 100-year period according to the EPA.

“No matter how you slice it, even out to 100 years, pound for pound you want to reduce methane. It should give you the bigger impact on the climate,” says Ian Faloona, a climate scientist at the University of California, Davis.

With 500,000 acres of land in rice production in California, this source of methane is not huge, but not entirely trivial.

A “magic key” from Finland

Moskowitz began running internet searches looking for a solution. In 2016 she found it. University of Montana scientist Shawn Devlin was working on exactly what she needed. Devlin’s research showed that adding fish to humic lakes in Finland, reduced methane emissions. A humic lake is one that has a lot of decomposing organic material in it. These lakes were similar to the ponds created by the flooded rice fields.

In his 2015 paper, Devlin wrote about how he and his colleagues introduced fingerling European perch into several small lakes in Finland. When the fish ate the zooplankton, they induced a trophic cascade, or a kind of domino effect in the food web. The fish ate the zooplankton, and the zooplankton practically disappeared. Without zooplankton there to eat them, the bacteria proliferated. Among those bacteria were methanotrophic bacteria, a type of bacteria that consume methane. They start out with methane gas and oxidize it to CO2. More methanotrophic bacteria meant less methane released into the atmosphere.

 “Coming across Shawn’s work was truly one of those moments,” said Moskowitz. “It was thrilling. It almost seemed like the magic key.”

Shawn Devlin is a science rock star, but he still gives you that “guy next door” feeling. He’s a father in his thirties. For him, searching for the answers to research questions is just what he does. He still has a hard time believing that he won the prestigious ASLO Award in limnology for his work.

 While Devlin had expected methane emissions to decrease, the Finland results were off the charts. “If you have fish present, you have about a ten times difference in the amount of methane leaving the system,” he said. The structure of the food web could be a really strong factor in regulating methane emissions in certain water bodies.


Through the Fall and the Spring, researchers collected water samples to study population and composition of zooplankton and microbacterial communities in these flooded fields, as well as dissolved methane in the water column.


Moskowitz was intrigued.

“I thought ‘my gosh, if it could work in a Finnish lake, maybe we could see if it could work in a rice field,’” she said.

 Sitting in his office at the Flathead Lake Biological Station, with its view of the largest natural freshwater lake west of the Mississippi, Devlin is supremely nice and unassuming. He remembers the day he first heard from Moskowitz.

“I got an email one day from a group in California saying ‘we just read your paper and it’s a good paper, and we’re interested in using those concepts to reduce methane in rice production,’” he said. Devlin told Moskowitz that he was on board.

Climate solutions?

Applying this concept had greater implications than RRI’s sustainable protein idea. If putting fish in the fields also reduced methane, it could potentially be implemented over a portion of the 500,000 acres of California rice lands. Scale this up to the other six states in the US that produce rice, or even globally, and it could make a difference.

Fish production in rice cultivation has been going on in Asian countries for over 1000 years, but a scientific protocol with the specific goal of reducing methane gas emissions and producing sustainable aquaculture operations would be new.

“If California does it and it’s successful, and economically feasible, and it’s implemented throughout Asia or somewhere else, it has the potential to be impactful, says UC Davis climate scientist Ian Faloona.

With a 2025 carbon neutrality goal looming in California’s future, rice farmers are seeing the pressure building like a thundercloud.

There have been some attempts to address the issue. The California Air Resources Board (CARB) spent years developing a methane emissions reduction protocol for rice farmers, but it hasn’t taken off. David Clergen, CARB public information officer, says there is really very little incentive under the current cap and trade program for farmers to implement the strategy. “At this point it’s a tough sell, he says. “We think over time, people may be able to make some adjustments and make it more realistic for them.”

The protocol involves draining and re-flooding fields. It reduces methane. It also reduces benefits to waterfowl. It’s expensive and potentially dangerous to the crop. It also involves the convoluted California water rights system, making it that much harder.

“In California water is money,” said Clergen.

Rice farmer Charley Mathews says that right now there’s no incentive for him to reduce methane using the CARB protocol, but he knows the problem isn’t going away.

“At some point we need to address it, he said. “If every other industry has to make a sacrifice to reduce greenhouse gas emissions, we’re going to have to do it too somehow, and this is a method to accomplish that as well.”

A flood plain in disguise? Conservation implications for fish

UC Davis fisheries scientist Andrew Rypel is a fisheries researcher working with Shawn Devlin on the Fish in the Fields Project. Shawn recruited him through their mutual friends who saw that they were both working on similar things.

 Rypel was already working on the Nigiri Project. The name is a humorous nod to sushi, referring to a thin strip of fish over compacted rice. Cal Trout and several collaborators started raising Chinook salmon fry in rice fields that adjoin the Sacramento River. Rypel’s work on this project makes him a natural fit for the Fish in the Fields project, which uses many of the same concepts.

He’s never seen a more politically charged area surrounding water and natural resources than California. He’s seen the “water is money” concept first-hand.

Despite the politics, he considers the Fish in the Fields Project to be one of the most exciting projects that he’s working on.

“One of the reasons I really like the project is that it goes way beyond California,” he said.

Rice is a globally grown crop, often produced in high greenhouse gas-producing countries in the Far East.

“It’s also applicable to just flood plains in general. It doesn’t have to be rice. “It’s a way of thinking that could encourage reductions in methane globally,” said Rypel.

A lot of the political nature of water in California revolves around endangered fish. The federal Endangered Species Act puts protections in place that affect the use of water. California has a number of federally threatened or endangered fish species that are endemic, or native to only that area. Many of these species were specially adapted to thrive in the Central Valley floodplain.

The Central Valley of California used to be a natural floodplain. Fish species like Chinook salmon would happily fatten up there before going on their journey to the Pacific Ocean. Now the floodplain is gone and the salmon are disappearing. Today only five percent of the original floodplain habitat remains. The rest has been taken over by human activities including the 500,000 acres in rice agriculture. Yoshiyama et al. estimated in 2011 that salmon populations in the Central Valley have decreased to under 75% of their numbers just since the 1950’s.

Managers are starting to eye artificial habitat for solutions because so little natural habitat is left. Rice fields can be viewed as surrogate floodplains.

“People have been sort of slowly realizing that ‘oh, you know, rice agriculture could be thought of as a floodplain if you thought about it the right way,’” said Rypel.

California Rice farmer Charley Mathews says that he thinks the main value of the Fish in the Fields Project for rice farmers lies in fish conservation programs. He’s seen it work well with waterfowl. As a businessperson he wants to get in on the ground floor of salmon rearing if the Nigiri project starts expanding to land-locked rice fields.

“I think at the end of the day they’re going to find that this is the best way to increase the salmon population. If it’s still fish and game and the Fish and Wildlife Service that are involved, they’re gonna look to the rice farmers that have a system of aquaculture already in place, and are able to take care of these fish,” he says.

In addition to conserving threatened or endangered native species, the project also has the potential to reduce pressure on ocean fish that are over-exploited.

Marine baitfish such as sardines, anchovies and herring are netted and used for bait, fertilizer, or aquaculture. It’s gotten bad enough that the sardine season has been closed off the coast of California for the last three years. Providing new areas to grow a farmed source of these popular bait species, could be huge for wild populations.

Food for the people

The Fish in the Fields project is also set up to do what it was originally designed to do--provide a much-needed carbon-neutral source of protein for people.


jars of phytoplankton from california rice fields

Not only do the fish growth 10x larger in these fields than in wild habitat, but the zooplankton populations are much lower in test ponds where fish were introduced. Soon, RRI will analyze all samples to learn more about those impacts on methane emissions.


More and more seafood in the world is originating from aquaculture. According to a World Bank Report released in 2013, 62% of world seafood will come from aquaculture by the year 2030. People are going to be increasingly relying on aquaculture for food. Rice farmers would have no problem selling the fish they grow in their fields as a second crop, adding to their bottom line.

In the experimental ponds, Rypel added golden shiner minnows and watched them explode into growth. Growth rates for the minnows were similar to what generally is seen in aquaculture. But the thing that sets this aquaculture operation apart is that they didn’t have to feed the fish.

 “We just filled the ponds up and they developed their own zooplankton community. We put the fish in and they grew like that. It wasn’t like there was a cost beyond the cost of the fish,” said Rypel.

The project is brimming with potential. The next steps are to get funding to start looking at the role of fish density on how much methane is produced, as well as how scalable the results are beyond the test ponds. A lot of it is still uncertain, but so far, it’s incredibly promising. “This is a real game changer,” says Devlin.

For updates and more information about Devlin’s work with the “Fish in the Fields” project, please visit the FLBS website at