Of the 160 million tons of seafood that end up on people’s plates each year, 50 percent comes (pdf) from aquaculture. Growing all that salmon, tilapia and shrimp requires a steady supply of the perfect food supplement: oily anchovies and sardines, often called forage fish, which are rich in proteins, fats and vitamins. About 90 percent of the 20 million tons of forage fish pulled from the wild each year is ground into meal or oil to nurture fish farmed for human consumption.

But with expectations aquaculture will continue to boom—the United Nations predicts production to increase by 34 percent by 2026—the industry is outgrowing its feed supply. This dilemma has spurred researchers to try to synthesize a stand-in that will provide the nutrients found in forage fish, be economically viable, yet not deplete resources such as grains that humans directly depend on for food. “Fish meal is important in aquaculture, and if [aquaculture] wants to grow, it has to break out of forage fish dependency,” says Michael Tlusty, a an associate professor of sustainability and food systems at the University of Massachusetts Boston. But “how do you come up with totally new products” to fill this need?

Even at current aquaculture production levels, high demand and limited supplies have made fish meal and oil too expensive to use for more than about 30 percent of a farmed fish’s diet. That amount provides enough of the necessary mix of nutrients (including coveted omega-3 fatty acids) to help some species grow faster and thus require less feed overall, says Halley E. Froehlich, a soon-to-be assistant professor at the University of California, Santa Barbara, who studies global aquaculture and fisheries. Most producers fill in the remaining calories with soy, grain and other cheap products.

But soy and grain are already under pressure to supply food for other farmed animals such as cows and pigs—and to directly sustain humans—says Jillian Fry, a seafood and public health researcher at the Johns Hopkins Center for a Livable Future at Johns Hopkins University. Rising demand for such crops is already driving deforestation and overloading waters with fertilizer runoff.

With all this in mind, researchers and start-ups are developing novel feeds from other resources. Some labs are looking to mimic forage fish by reaching one step back in the food web to the algae forage fish themselves eat, and that are the source of those prized omega-3’s and other micronutrients. Pallab Sarker, an associate research professor of sustainable aquaculture at the University of California, Santa Cruz, and his team found Nile tilapia gain more weight on less feed—and contain more omega-3’s—when they consume a particular algal species instead of the usual fish oil; this suggests algae could be a viable replacement fish fatty acid source for this species of farmed fish. Research in other labs suggests similar microorganisms could substitute a portion of fish products fed to red drum and Atlantic salmon.

Algae are not the only alternate organisms researchers are looking at. Margareth Øverland, a professor with Foods of Norway at the of the Norwegian University of Life Sciences, is testing whether a particular protein-rich yeast, grown on Norwegian spruce wood and seaweed sugars, could be an ersatz fish feed. “The yeast is sustainable because it can be produced independent of arable land, uses little fresh water and can use low-value biomass” for which humans have little food use, she says. Atlantic salmon that had a third of their diet converted to this yeast gained weight as fast as their conventionally fed counterparts, Øverland and her team found. To make the product easier for fish to digest, the researchers are tinkering with their yeast strain and the combinations of sugar they feed it to see if that helps it go down fish gullets more smoothly.

Other researchers are experimenting with everything from bacteria to crickets as forage fish substitutes. Some, although not Sarker or Øverland, are competing in a contest called the F3 Challenge to see who can sell as much of their oil substitute as possible in an effort to push innovation, Tlusty says.

For most researchers, scaling up presents the biggest hurdle. Replacing the 22 million tons of wild aquaculture fish used every year will require massive volumes of microalgae production. “Our lab can’t meet the quantity we’d need to meet feed levels,” Sarker says. That production level is also required to drop the price, because otherwise farmers will still opt for the adequate and cheap grain, he adds. He hopes to reach these goals by using by-products from other companies that harvest algae for human dietary supplements and other goods. “This one product will help the micro-algae industry to grow with another stream of revenue,” he says.

Inherent to the problem of ramping up production of these feed substitutes is nailing the right ratios of fatty acids, such as omega-3’s. Mimicking the natural balance found in fish oil requires one of two methods: Researchers must either find the perfect algal or yeast strains and feed it the right starter, so associated microbes produce everything in proportion—or they must combine fatty acids from various sources, which makes coordinating production even more difficult.

Even if that delicate balance of nutrients can be reproduced, and algae or yeast scaled up to the needed levels, questions remain—such as how much greenhouse gas the imitation feed refinery processes will emit. These feed ideas are still so young it is hard to do the math on that, Tlusty says, though current industrial fermentation processes, like beer brewing, hint at what emissions could look like.

Overcoming the various hurdles and answering those questions may be crucial to maintaining human food-production systems without adding to the mounting pressures on marine ecosystems from overfishing and climate change. “Aquaculture is producing more,” Tlusty says, “and we need to make sure as a responsible industry we have all future scenarios mapped out.”