Researcher Creates Soy Feed To Keep Fish On The Table

"We've maxed out the ocean fisheries," says Purdue aquaculturist Paul Brown. "For example, eight or nine strains of Pacific salmon are now on the rare or endangered species list. We need an alternative. To meet global demand in the future, aquaculture must grow."

For aquaculture to grow, producers need new sources of fish food. Fish meal, which is dried and ground fish that is the traditional food for farm-raised fish, is getting more expensive and harder to find, Brown says. He sees plant proteins as the logical alternative, and soybeans as the best source of plant protein. Also, according to Brown's tests, fish that eat soy-based feed excrete less phosphorus and nitrogen than do fish that eat fish meal. That means they're less likely to cause pollution problems.

Brown predicts that with the world's current population growth and declining wild fish populations, farmers in the year 2035 may produce as many pounds of fish as chicken. If those fish were fed a soy-based diet, they would consume the equivalent of between 40 percent and 90 percent of the current soybean output of the United States. And much of the food fed to those farm-raised fish will be developed from nutrient studies and feed formulations now being done at Purdue, he says.

Last year, a new soy-based, commercial feed developed by Brown for yellow perch reached the market. Brown picked yellow perch because they produce the lowest-fat fish fillet in the United States and because without aquaculture, supply can't meet demand. The yellow perch population in the Great Lakes has plummeted so that current harvests are about one quarter of what they once were.

With funding from the Indiana Soybean Board, Brown figured out which nutrients yellow perch need to grow properly, then found a way to get those nutrients out of a mix mostly made of soybeans and corn. When he compared growth of grain-fed perch to perch fed the highest quality fish meal, he found no difference. And the grain-fed perch produced quality fillets.

Trout make another good-quality fillet. Fish farmers currently produce 60 million pounds of trout per year, and the market is growing. Soy-based feed could help bring more economical trout fillets to grocery counters.

Brown came up with a feed formulation that, in small-scale trials, put a pound of meat on a trout for every pound of food the fish ate. The new trout food, developed with a regional grant from the U.S. Department of Agriculture, is three-quarters soybean and corn meal, with some added fish oil. Eventually, Brown says, he'd like to replace the fish oil with oil from a plant such as canola. He's testing it now in commercial-scale aquaculture ponds. He also gave the formulation to a producer who plans to try it.

Brown's also detailing diets for lobsters.

"The lobster industry is growing, but producers face a shortage of feeds," Brown says. "Their main food has been cod racks – the cod head, bones and guts left after processors take off the fillets. As of two years ago, the North Atlantic Ocean was considered overfished, and there's a shortage of cod. Plus, cod racks don't keep well in storage. Lobster producers need a more storable feed."

Restaurateur Frank Crohn, a Purdue alumnus who lives in Maine, thought that soybean-based feeds would fit the bill. Through Brown, he hired a postdoctoral student to tailor-make food for the American lobsters he puts on his menu. The researchers, who had done similar diet development for spiny lobsters in the last five years, worked out a formulation that's now ready for testing on a commercial scale. Both Crohn and Brown will run tests to see how well lobsters perform on the feed.