Scientists find key to vegetarian diet for fish raised in aquaculture

August 29, 2012

As warning bells clang about the decline of ocean fisheries and contaminant levels in fish, scientists from the University of Maryland Center for Environmental Science have found the key to raising some marine fish on a vegetarian diet. The study found that cobia—a fast-growing fish well-adapted to commercial aquaculture—can grow just as well on a plant-based diet as a diet of fishmeal, as long as the essential amino acid taurine is added to the mix. 

In the world of commercial aquaculture—growing fish in tanks instead of catching them from the oceans or streams—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 fishmeal, and must be caught in the wild to feed them. This is expensive (for example, it takes 6 kg of wild fish to make 1 kg of salmon), and it further depletes the world’s fisheries. 

“Aquaculture isn’t sustainable because it takes more fish to feed fish than are being produced,” said study author Aaron Watson, who conducted his research with Dr. Allen Place at the Institute of Marine and Environmental Technology in Baltimore, Maryland. “But a new vegetarian diet might change everything.”

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

Taurine, an amino acid often used by body builders and added to energy drinks, is also found in high concentrations in carnivorous fish and their prey, as well as fishmeal. However, it is not found in vegetarian alternatives to fishmeal. The researchers proved that taurine is integral to a vegetarian diet to ensure the growth of these top-of-the-food chain fish.

In addition to the potential to turn aquaculture into a more profitable enterprise and ease the pressure on catching wild fish, raising fish on a vegetarian diet also means cleaner fish to eat, with levels of PCBs and mercury as much as 100-fold lower.

“Right now, you are only supposed to eat striped bass once every two weeks,” said co-author Dr. Allen Place.  “You can eat aquaculture-raised fish twice a week because levels are so low.”

Preliminary taste tests have shown that there’s no difference between the taste of fish on the vegetarian or fish meal diets.