Eating fish is good for us, but what should the fish eat?

Increased use of plant-based ingredients in aquaculture feed could impact the nutritional benefits of eating seafood, according to a study that examined the environmental health implications of crop-fed fish.

While wild fish find their own food — which includes smaller fish for carnivorous species — intensively farmed fish are fed a manufactured aquaculture feed. This feed was until recently composed of high levels of fishmeal and fish oil derived from wild fish, but this has become unsustainable, prompting a shift to plant-based ingredients such as soybean meal. The use of crop-based ingredients in the US is projected to increase 124% between 2008 and 2020.

“Farmed fish get their health-promoting omega-3 fatty acids, EPA and DHA, from their feed, and specifically from fish oil,” said study leader Jillian Fry, PhD, director of the Public Health and Sustainable Aquaculture Project at Johns Hopkins Center for a Livable Future. “Our review found that increasing plant-based ingredients can change the fatty acid content in farmed fish, which can affect human nutrition.”

‘Environmental Health Impacts of Feeding Crops to Farmed Fish’, published in the journal Environment International, estimates the environmental footprint for the top five crops used in commercial aquaculture feed. The shift to crop-based feed has been hailed by some as a positive change in light of the increasingly depleted oceans and the rapidly expanding aquaculture industry, but the change may also have some unintended consequences.

Using vegetable oils instead of fish oil changes the fatty acid content of fish and nutritional value for human consumption, the researchers said. Dietary guidelines encourage us to consume seafood high in omega-3 fatty acids, which promote improved cardiovascular health and neurodevelopment, so this could have implications for dietary recommendations and the aquaculture industry. More research is needed, they said, to better understand the impact of this shift in feed on the health benefits of consuming farmed fish.

And while fish-based ingredients are limited, so are the resources such as land, water and fertiliser used to produce feed crops. Aquaculture’s environmental footprint may now include increased nutrient and pesticide run-off from the industrial crop production needed to supply fish food. This run-off is a key driver of water pollution globally and can negatively impact public health. 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 air, water or soil contaminated by nutrients and/or pesticides.

Fry believes the nutritional content of farmed fish should be monitored and the aquaculture industry should assess the environmental footprint and public health impacts of crop-based feed ingredients and seek to develop sustainably produced alternatives.

Originally published here.