Ocean fisheries could benefit from research using distillers grain, the high-protein co-product of ethanol production, to partially replace fish meal in aquaculture diets.

Professor Michael Brown in South Dakota State University’s Department of Wildlife and Fisheries Sciences said the studies are part of SDSU’s ongoing exploration of using plant protein in fish feeds. Brown’s upcoming studies include diets containing a high protein, dried distillers grains with soluble (DDGS) produced by some corn ethanol plants. He’ll include that 42 percent protein product as one component in the diets of rainbow trout and yellow perch.

To sustain production, fish farmers need to include enough protein in the diets of fish they raise for human consumption, Brown said. Traditionally, the largest share of that protein has come from fish meal derived from ocean species such as menhaden, anchovies, herring, and sardine.

“That’s one of the key problems right now – the marine fisheries where we derive most of our fish meals that go into commercial fish feeds have been depleted. Some have been over-harvested and some are on the border of collapse,” Brown said. “ Similar to any commodity with low supply and high demand, fish meal prices continue to increase, driving fish production costs higher. For these reasons we need to develop alternatives.”

Brown, who also includes soybean meal and other soy products in experimental fish diets, said aquaculture feeds could provide a new market for farmers’ corn and soybeans.

“Plant proteins from sources such as soybeans and dried distillers grains are readily available. We can replace a certain amount of that fish meal with these plant-based proteins and achieve successful grow-out. That’s the bottom line ,” Brown said.

SDSU’s aquaculture studies have used DDGS in fish diets for the past few years. But that work was done with conventional DDGS of about 29 percent protein and about 8 to 10 percent lipids. Brown found that aquaculture feeds could include up to 20 percent of such DDGS products in tilapia feeds without greatly impacting performance, and similarly up to about 40 percent in yellow perch feeds under experimental conditions.

“We were trying to determine the maximum amount that we could include in the diet without adversely affecting growth performance and other metrics of fish production, such as feed efficiency and fillet or dress-out percentage,” Brown said. “The DDG experiments we’ve planned this next year are with yellow perch again, but we’re trying some different products. These will be dried distillers grains with solubles, but these will be about 42 percent protein, so they’re relatively ‘hot,’ if you will, in terms of the protein content. The lipid (fat) levels are reduced a little bit compared to the traditional DDGs, but we can supplement low-level combinations of plant and fish lipids in those diets.”

An entirely separate but parallel experiment will use the 42 percent DDGS in rainbow trout diets. Previous work by researchers in another state found that rainbow trout did well in diets that included up to 17.5 percent conventional DDGS.

“Our first experiment will be to apply these new products to rainbow trout feeds, and we’ll investigate inclusion levels from 0 up to 100 percent of the fish-meal component, and we’ll see where performance declines,” Brown said. “We won’t know until we ask the animals and see what they like – what will accommodate growth performance and survival.”

Funding for the research comes from the South Dakota Agricultural Experiment Station and the U.S. Department of Agriculture’s Agricultural Research Service.