Shift in farmed fish feed may affect nutritional benefits of eating seafood

The fish-farming industry is increasing its use of plant-based ingredients in its feed and moving away from traditional feed made from fish, a shift that could affect some of the health benefits of eating certain types of seafood, according to a new analysis from the Johns Hopkins Center for a Livable Future.

Fish farming, also known as aquaculture, is the fastest-growing food animal sector, outpacing the beef and poultry industries. While wild fish find their own food—which includes smaller fish for carnivorous species—intensively farmed fish are fed a manufactured aquaculture feed. Until recently, manufactured feed was typically composed of high levels of fishmeal and fish oil derived from wild fish, but it has become unsustainable to catch enough wild fish to feed growing numbers of farmed fish.

Image caption: Jillian Fry

As a result, the industry has shifted the makeup of the feed—the use of crop-based ingredients is projected to increase 124 percent between 2008 and 2020. The shift has been hailed by some as a positive change in light of the increasingly depleted oceans and the rapidly expanding aquaculture industry, but there may also be unintended consequences.

"Farmed fish get their health-promoting omega-3 fatty acids, EPA and DHA, from their feed, and specifically from fish oil," says study leader Jillian Fry, director of CLF's Public Health and Sustainable Aquaculture Project and a faculty member at the Johns Hopkins Bloomberg School of Public Health. "Our review found that increasing plant-based ingredients can change the fatty acid content in farmed fish, which can affect human nutrition."

The new study, published online in the journal Environment International, details the industry shift to crop-based feed ingredients, such as soy, corn, and wheat. Using vegetable oils instead of fish oil changes the fatty acid content of fish and nutritional value for human consumption, the researchers say.

Omega-3 fatty acids promote cardiovascular health and neurodevelopment. Considering that Americans are encouraged to consume seafood because of its omega-3 fatty acid content, the industry shift has large-scale implications for dietary recommendations. Also, aquaculture's environmental footprint likely now includes increased nutrient and pesticide runoff from the production of manufactured feed. This runoff is a key driver of water pollution globally, and depending on where and how feed crops are produced, plant-based fish feed could be indirectly linked to negative health outcomes for agricultural workers and nearby communities due to exposure to contaminated air, water, or soil.

According to the study, more research is needed to better understand the impact of this shift on the health benefits of consuming farmed fish. Fry says that these new findings may raise more questions than they answer.

"The nutritional content of farmed fish should be monitored," Fry says. "The aquaculture industry should assess the environmental footprint and public health impacts of their crop-based feed ingredients and seek those produced using sustainable methods."