Inside something similar to a beer-brewing vat, at a biotech accelerator in San Francisco, a startup spent the last four months tweaking a process to grow fungi that it then turns into a “salmon” burger that looks, tastes, and smells like the actual fish. Side by side with a salmon burger from Whole Foods, the fungi-based burger is nearly indistinguishable.

“We asked ourselves, is there something in nature–that isn’t a plant–that has the same size of fiber as animal muscle fiber?” says Kimberlie Le, cofounder and CEO of Terramino Foods, one of several startups that will graduate today from Indiebio, an accelerator that helps scientists launch companies. The structure of plants makes it difficult to replicate the texture of chewing on meat. Plants high in protein also tend to have strong flavors. Fungi, they discovered, addressed both of these problems. After algae and plant-based ingredients are added to the fungi, the burger also has the same flavor and nutrition as salmon.

Le and cofounder Joshua Nixon met as students at the University of California-Berkeley, where both enrolled in an undergraduate class called Plant-Based Seafood Collider, where students experimented with creating alternatives to fish. While plant-based meat is growing quickly as an industry–meat giants like Cargill and Tyson have invested heavily in companies like Beyond Meat and Memphis Meats, which make alternates to traditionally farmed meats (the former makes plant-based versions of beef and chicken, the latter grows meat in a lab from animal cells), and Impossible Foods now sells its plant-based burger at a fast-food chain–alternatives to seafood have gotten less attention.

At the same time, humans consume more seafood than any other protein source, and that consumption is growing. Seafood, like meat, poses multiple environmental challenges. Overfishing is already a widespread problem. Pollutants like mercury, flame retardants, and microplastics sometimes show up in fish. Some salmon farms use large amounts of antibiotics.

“We were looking at a lot of the efficiencies of the production of what in some cases are food products that then get ground up and put into fish fingers or fish cakes or fish paste . . . there’s a wide range of different places where a fish could be replaced without losing the taste of the product,” says Allison Berke, an academic research advisor for the Good Food Institute, a nonprofit that mentored students in the class and a series of related classes focused on alternative meat that followed. During the class, students focused on finding ways to replicate the taste of fish, along with texture. While other students in the class worked with plant proteins, Le and Nixon used fungi.

Le and Nixon have experimented with various fungi, but are particularly interested in using koji, a fungus commonly used to make sake, miso soup, and soy sauce. (Koji, or Aspergillus oryzae, is well-known enough in Japan that it has inspired a manga series and, after being named “national fungus,” is celebrated each year on October 12.) “Instead of using [koji’s] ability to transform soy or rice, we’re using their biomass as a great source of protein,” says Le.

The startup brews the fungus in a liquid, feeding it on simple nutrients, and as it grows into strands they harvest it to use as an ingredient. On its own, the fungi are nearly flavorless. Algae, another key ingredient, helps give the burger its characteristically fishy flavor and provides omega-3 fatty acids. The resulting product has less fat than farmed salmon but otherwise is nutritionally the same. Like meat, it is a complete protein source.