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Smaller fish offer better nutrition and lower environmental cost, Amazon River study finds

Smaller fish species are more nutritious, lower in mercury and less susceptible to overfishing, a Cornell-led research team has found.

The team's study was conducted in the Amazon River, but the findings have implications for biodiversity conservation and public health across the globe as large fish species populations are declining worldwide.

The study, "Accessible, Low-mercury and Nutritious Fish Provide Win-Wins for Conservation and Public Health," Jan. 17 in One Earth. It was authored by four Cornell researchers and colleagues from Brooklyn College and the Wildlife Conservation Society, a nongovernmental organization.

"Fish can provide a nutritious source of food at lower environmental cost than other animal-sourced foods, but fish can also potentially expose consumers to mercury contamination, and overexploitation of oceans and rivers harms biodiversity," said first author Sebastian Heilpern '10, a Schmidt AI in Science Postdoctoral Fellow in the College of Veterinary Medicine (CVM).

"Often, these risks vs. benefits are looked at in siloes," Heilpern said, "but we wanted to look at them holistically."

The researchers analyzed nutritional value, mercury content, price and abundance for 59 fish species in the Amazon River. They found that smaller species that are more common and less expensive are also more nutritious and lower in mercury.

Worldwide, larger fish species tend to have the highest levels of mercury, because the element accumulates in their tissues as they live longer and eat other mercury-contaminated organisms. The problem is especially acute in the Amazon because of the expansion of poorly regulated gold mining that uses mercury to separate gold from river sediments.

The Amazon is one of the most biodiverse regions in the world. Roughly 2,500 species of fish exist in the Amazon River, and about 100 different species are sold for consumption, Heilpern said. Helping people get the best nutrition from limited resources is a key priority, especially as population growth and climate change put even more pressure on natural resources, he said.

Though this research was conducted in the Amazon, many findings are more broadly applicable. For example, though humans tend to prize larger fish species, for cultural reasons and easier preparation, globally, larger fish have higher mercury levels and are more vulnerable to human pressures.

Larger species such as goliath catfish, tuna and salmon are more likely to take long migratory routes; especially for freshwater species, these routes can be interrupted by dams and other habitat interruptions that further jeopardize reproduction.

Smaller fish are less susceptible to overfishing, in part because they have faster reproduction cycles, which may also make them more nutritious because micronutrients like iron and zinc fuel cell metabolism and growth, Heilpern said.

Public health messaging should incorporate a more holistic view of the nutritional and environmental impacts of eating a variety of fish, the researchers advocate.

"Human food systems are a huge driver of biodiversity loss in the environment. At the same time, biodiversity in our food systems sustains the nourishment that humanity depends upon," Heilpern said. "My hope is that this information can help provide guidance and identify solutions so that our food systems can become more sustainable, for the benefit of human health and ecological systems."