U.S. researchers say they\'ve turned a greedy carnivorous fish into a vegetarian, a result that could protect smaller fish in the marine food chain. Cobia -- sometimes known as black salmon -- are a sleek and powerful fish that devour crab, squid and smaller fish. Researchers in Baltimore sought to change farm-raised cobia into vegetarians to ease pressure on the ocean\'s stocks of small fish -- menhaden, anchovies and sardines -- being pressured intensely by industrial fishing to provide fish feed to aquaculture. Feeding farm fish from wild fisheries is environmentally unsustainable, experts have said. The researchers -- Aaron Watson, Frederic Barrows and Allen Place -- said they\'ve come up with a combination of plant-based proteins, fatty acids and a powerful amino acid-like substance found in energy drinks to convert the carnivorous cobia and another popular farm fish, gilt-head bream, into vegetarians. \"It would take the pressure off harvesting the menhaden fishery,\" Place told The Washington Post. Menhaden -- bony and oily little fish vital as part of the marine food chain, feeding many marine animals including dolphin, swordfish and birds -- are severely overfished for oil, animal feed and sport-fishing bait. The work in Baltimore could lead to satisfying human demand for seafood without depleting the wild stocks that aquaculture was meant to save, said Michael Rust, aquaculture research program manager with the National Oceanographic and Atmospheric Administration. \"All fish -- carnivore, herbivore and omnivore -- require about 40 nutrients in the correct ratio,\" Rust said. \"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.\"