Ethanol Co-Products Could Lower Cost of Freshwater Fish Production

Add this to the list of ethanol's potential benefits: lowering the cost of fish production.

Fish feed is a major expense for many aquaculture operations. New research by Agricultural Research Service (ARS) scientists shows that ethanol co-products can provide protein for fish feeds at a lower cost than the soybean-corn combinations commonly used.

The recent proliferation of ethanol processing facilities has led to a surplus of distiller's dried grains with solubles, or DDGS—a nutrient-rich processing co-product that is often used to feed livestock.

DDGS is relatively protein-rich and lacks some of the undesirable characteristics that make many plant protein sources less suitable for use in fish feeds. In addition, DDGS is cheaper and more palatable to fish than soybean-corn combinations. However, it lacks some essential amino acids, such as lysine.

In the ARS Aquatic Animal Health Research Unit at Auburn, Ala., nutrition scientist Chhorn Lim and his colleagues are evaluating how diets including DDGS influence growth performance and disease resistance in catfish and tilapia.

The scientists gave the fish feeds that included 0, 10, 20, 30 or 40 percent DDGS. All five feeds had similar levels of energy, protein and fat. Results showed that tilapia thrive on feed with up to 20 percent DDGS. Adding supplemental lysine to the feed increased that percentage to 40 percent.

The scientists found that catfish thrived on feed comprising up to 40 percent DDGS plus lysine. In addition, they observed that catfish raised on diets that included DDGS demonstrated greater resistance to at least one major disease: enteric septicemia of catfish. Catfish raised on DDGS-containing diets were more likely to resist infection.

Surviving catfish raised on a diet without DDGS had fewer antibodies than those raised on the DDGS feed—particularly fish on the 20 percent DDGS diet, whose antibodies were significantly higher than those of the control fish.

This work has potential economic benefits for both ethanol and aquaculture. Finding markets for DDGS is essential to economical ethanol production. And substituting soybean-corn combinations with a cheaper protein source could help reduce the cost of fish feed, thereby reducing overall production costs.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.