Will plant-based fish food make aquaculture more sustainable?

Using plants comes with many of its own environmental trade-offs, as we’ve learned from extensive reporting on the resources needed to feed livestock. Wesley Malcorps, a Ph.D. student at the University of Stirling in Scotland, wanted to know what exactly those trade-offs would look like for farmed seafood, particularly shrimp.

“Aquaculture is the fastest growing food sector in the world at the moment,” Malcorps says in a phone interview, citing a report on aquaculture from the 2018 Fisheries and Aquaculture Organization of the United Nations (FAO). “However, if we want to sustain the current aquaculture growth that we see…we need a lot more aquafeed.”

Using data collected from prior scientific research and FAO, Malcorps created a mathematical model that calculated the land, water, and fertilizer use for various combinations of fishmeal and plant-based inputs like soy—a common substitute for fishmeal—or a soy-free canola- and pea-based feed (research on these plant alternatives is more nascent compared with soy).

To design realistic combinations of fishmeal and plant-based ingredients, he used proprietary feed formulation software. Malcorps focused on two popular species of farmed shrimp: whiteleg and black tiger. For each, he created a baseline feed that included high levels of fishmeal, then a series of other feeds with incrementally less fishmeal and proportionally more plant-based substitutes.

Malcorps found that an increase in plant ingredients was directly correlated with an increased toll on freshwater and land resources. This was the case for both whiteleg and black tiger shrimp, with both soy and non-soy plant ingredients. The latter also demanded significantly more land and fertilizer use than soy ingredients. Crops like rapeseed (which produces canola) and pea plants may have higher resource demands compared to soy, Malcorps notes.

The implications here aren’t negligible. If aquaculture companies use increasing amounts of plant-based ingredients for fish feed, those changes can aggregate into a consequential change in land farming.

“The continuing trend of increased inclusion of terrestrial plant-based ingredients may lead to competition for land, causing social and environmental conflicts, which may in turn affect the resilience of the global food system,” the study notes.

In a globalized world, food production doesn’t—can’t—operate in a vacuum. Instead, it interweaves human and natural systems, on land and in water. Any change in one sphere is bound to cause reactions in others. The takeaway is that neither fishmeal nor plant-based feed is clearly better for the environment than the other.

“It’s about looking at the strategic inclusion of these ingredients in relation to their availability,” Malcorps says. “It’s about finding a balance between the marine and terrestrial ecosystems—because both systems are under pressure.”