Scientists discover key to easing reliance on wild-caught fish

University of Maryland researchers have developed a plant-based diet that can support marine carnivore fish raised in aquacultural systems.

For the first time, scientists have been able to develop a completely vegetarian diet that works for marine fish raised in aquaculture, the key to making aquaculture a sustainable industry as the world's need for protein increases. The study, by Aaron Watson and Allen Place at the University of Maryland Center for Environmental Science's Institute for Marine & Environmental Technology, was published in the August issue of the journal Lipids.

"Aquaculture isn't sustainable because it takes more fish to feed fish than are being produced, but a new vegetarian diet might change everything," Watson said.

Supported by another paper published in the Journal of Fisheries & Aquaculture, the team has shown that a completely plant-based food combination can support fast-growing marine carnivores like cobia and gilthead sea bream in reaching maturity just as well as — and sometimes better than — conventional diets of fish meal and fish oil made from wild-caught fish.

Nearly half of the world's fish and shellfish supply is supplied by aquaculture — growing fish in tanks or ponds instead of catching them from the oceans or streams — and scientists have been trying to figure out how to make growing fish sustainable. Many high-value fish such as cobia, sea bream and striped bass are predators and eat other fish to survive and grow. As a result, their food in captivity is made of a combination of fish meal and fish oil, and must be caught from the wild to feed them.

"This makes aquaculture completely sustainable," Place said. "The pressure on natural fisheries in terms of food fish can be relieved. We can now sustain a good protein source without harvesting fish to feed fish."

The replacement of fish meal and fish oil in aquaculture diets has been a goal for researchers for decades but has met with limited success. The team's research centered on replacing fish meal with a blend of plant protein sources to completely eliminate the need for fish meal and fish oil in diets for cobia and other high-value marine carnivores.

Fish meal was replaced with a food made of corn, wheat and soy. Fish oil — expensive and scarce due, in part, to its popularity as a health supplement for people — was replaced with soybean or canola oil, supplemental lipids from algae sources and amino acid supplements, such as taurine.

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