Fishermen catch a cobia at a fish farm off the coast of Penghu County, July 26, 2007. (Sam Yeh/AFP/Getty Images)

Cobia is a sleek and powerful fish that devours flesh and doesn’t apologize for it. Open its belly and anything might pop out — crab, squid, smaller fish, you name it.

Recently, three Baltimore researchers — Aaron Watson, Frederic Barrows and Allen Place — set out to tame this wild and hungry fish sometimes called black salmon. They didn’t want to simply domesticate it; hundreds of fish farmers have already done that. They sought to turn one of the ocean’s greediest carnivores into a vegetarian.

The researchers announced last week that they pulled off the feat at a laboratory in the Columbus Center in downtown Baltimore. Over the course of a four-year study, Watson said, they dabbled with mixtures of plant-based proteins, fatty acids and a powerful amino acid-like substance found in energy drinks until they came up with a combination that cobia and another popular farm fish, gilt-head bream, gobbled down.

The conversion of these carnivorous fish to a completely vegetarian diet is a first, according to the University of Maryland Center for Environmental Science, and a key to breaking a cycle in which the ocean’s stocks of small fish — menhaden, anchovies and sardines — are plundered by industrial fishing partly to provide fish feed to aquaculture, one of the fastest-growing economic sectors in the world.

“It would take the pressure off harvesting the menhaden fishery,” Place said, referring to the bony and oily little fish billed as the most important in the sea. Menhaden, caught off Virginia’s coast, feed a plethora of marine animals, including dolphin, swordfish and birds.

The research was published in this month’s issue of the journal Lipids and is supported by a paper published earlier in the Journal of Fisheries and Aquaculture. It’s part of a race to replace feed from wild-caught fish as the diet of choice for farm-raised fish, set in motion by the National Oceanic and Atmospheric Administration and the Department of Agriculture in 2007.

Feeding both farm fish and more than a billion humans from wild fisheries is environmentally unsustainable, according to NOAA and just about every nonprofit conservation organization that monitors oceans.

Fearing that menhaden are severely overfished by an industry that sells it worldwide for oil, animal feed and sport-fishing bait, the Atlantic States Marine Fisheries Commission in December sharply reduced the amount that can be harvested.

Aquaculture was once thought to be a solution to overfishing in the world’s oceans, lakes and rivers. After the explosion in the human demand for seafood, the need to feed farm fish started depleting the stocks aquaculture was supposed to save.

But there is a way for people to have abundant fish and eat them, too, said Michael Rust, aquaculture research program manager at NOAA’s Northwest Fisheries Science Center.

“All fish — carnivore, herbivore, and omnivore — require about 40 nutrients in the correct ratio,” Rust was quoted as saying on NOAA’s Web site. “It doesn’t matter to the health of the fish where the nutrients come from. By incorporating marine algae, fish processing trimmings, and a variety of plant products, we can formulate high quality fish feeds without relying on wild-caught fish.”

The unproved observation faced nothing but obstacles. No one had created a plant-based alternative to the food carnivorous fish eat. And even if they had, when it comes to aquaculture, the United States is a small player in a big pond. Most aquaculture happens in Asia.

On the other hand, the United States is the brains behind the development and commercialization of animal feeds of all types and stands to one day greatly influence what China and India feed the multitudes of fish they raise in tanks.

Cobia is all the rave in Europe and Asia, and is a growing delicacy in the United States, where tuna, salmon and grouper reign as the meat-eating fish that meat-eating humans prefer.

In 2009, Watson set out with a NOAA grant to demonstrate that cobia could live without eating meat. With the help of Place and Barrows, he sought to show that a veggie diet would also reduce the amount of contaminants, such as polychlorinated biphenyls (PCBs) and mercury, absorbed by wild fish feeding in polluted waters and consequently by the humans who eat them.

A diet free of fish meal was not an easy recipe. Fish eat meat for protein, so the researchers had to give them plenty of that. They needed to come up with the right mix of lipids — fats, waxes and such — that fish also need to survive. Finally, they needed to supplement it with the right dose of a crystalline acid called taurine, the stuff that gives drinks such as Red Bull their energy jolt.

Watson said close attention was paid to feed eaten by herbivores such as trout. For a while, he relied on barley for protein. “Cobia were very sensitive to it,” he said. He saw when he squeezed the waste out of the fish that it wasn’t properly digested. They tried gluten, but that slowed the fish’s growth.

When the researchers tried a combination of soybean concentrate, protein concentrate, wheat flour and soybean meal, they made progress. The pellets that worked “are 15 to 20 percent more expensive than the commercially available feed,” Watson said. On the other hand, the cobia grew bigger and absorbed fewer contaminants.

“There’s no way you will ever in our lifetime get menhaden that’s not contaminated with PCBs and mercury, because of power plants, coal-burning and so forth,” Place said. “The products we have have very little PCBs and mercury. You’ve lowered the contaminant load that humans are eating.”