Aquaculture Magazine

Octuber-Novembrer 2016

Sustainable feeds IS THERE A CORN/SOY DIET FOR AQUACULTURE?

Producing high quality animal protein at minimal cost has been a goal of humans for millennia, and a promise from kings and politicians for over 400 years.

By: Paul B. Brown and Budi Tangendjaja1

The following quote was attributed to King Henry IV (1553-1610) of France, “I want there to be no peasant in my realm so poor that he will not have a chicken in his pot every Sunday”. In 1928, Herbert Hoover (1874-1964) promised “…. a chicken in every pot and a car in every garage” if elected president of the United States. Kings and politicians probably had little influence on current production of poultry, but production of meat birds serves as an example of high-volume low-cost production of animal protein; an example aquaculture has been attempting to mimic for several decades.
Numerous factors have contributed to the efficient production of poultry. Three of the more commonly discussed factors are selection for rapid growth, enhanced muscle development, and achieving these selection parameters when fed a standard diet containing soybean meal (SBM) and corn grain.  There have been several attempts to establish standard diets for various aquatic species, but this has been a challenge in the face of rapidly changing commodity prices, particularly fish meal and fish oil prices.  Poultry production also migrated away from fish meal in favor of a SBM/corn grain combination of ingredients. However, this basic dietary combination of ingredients is insufficient in crude protein and essential amino acids to meet the nutritional needs of aquatic animals.
Two processed corn products have received the bulk of the consideration in aquafeeds, corn gluten meal (CGM) and distillers dried grains with solubles (DDGS). Use of CGM is limited by price and pigment concentrations; muscle of aquatic animals tends to retain the yellow pigment from corn.  Use of CGM is commonly restricted to less than 10-15 % of the diet. Use of DDGS offers more promise largely due to more moderate pricing, but the crude fiber concentration is higher than preferred in aquafeeds. The rapid expansion of ethanol production as a fuel resulted in a modified DDGS that is lighter in color and effectively a different product from the traditional DDGS from the alcoholic beverage industries. More importantly, a high-protein DDGS has become available that contains lower concentrations of crude fiber, and is moderately priced. Nutritional comparisons of fish meal (FSM), high-protein DDGS, traditional DDGS and soybean meal (SBM) are presented in Table 1. Corn products commonly have lower concentrations of lysine than soy products, but soy products commonly have higher concentrations of methionine; two of the most limiting essential amino acids in feed ingredients. Thus, mixing SBM with corn products alleviates the essential amino acid deficiencies of both products and this has served as the basis for use in poultry and swine diets. Under the leadership of the US Grains Council, there is a renewed interest in DDGS as a complimentary ingredient in aquafeeds.
Feeding trials are underway in several countries, with an emphasis on the rapidly expanding aquacultural production in Vietnam. Data from two trials are presented here; one with tilapia, the other with Pangasius catfish (Tra). In both trials, DDGS was incorporated into practical diets and fed to the target species until market weight was achieved. Data from both trials indicates no negative impact of DDGS up to 15% of the diet. Further, color of fillets of both species was not different across treatments. In the tilapia trials, feed conversion ratio decreased from 2.5 in fish fed 0 % DDGS to 2.1 in fish fed 15 % DDGS.  Feed conversion was not different in the Tra study averaging 1.5-1.6 across all treatments.  Costs of the major ingredients are presented in Table 2. The trials reported here used the lower protein DDGS, but appear encouraging, particularly in diets containing relatively low protein concentrations (26-30 %). With increasing availability of high-protein DDGS, future trials will focus on additional species in high producing areas of the world.
Major agricultural crops offer significant potential in the rapidly expanding aquaculture market simply due to volume and consistency of product produced. Significant global increases in corn and soybean plantings helped stimulate the availability of poultry and swine as low-priced, high quality animal protein. A SBM/DDGS combination of major ingredients in aquafeeds might be the corn/soy combination needed to continue the rapid expansion of aquacultural production. Perhaps even to the point where we might see a fish in every skillet, and perhaps even more than once per week.

Dr. Paul Brown is Professor of Fisheries and Aquatic Sciences in the Department of Forestry and Natural Resources of Purdue University. Brown has served as Associate Editor for the Progressive Fish-Culturist and the Journal of the World Aquaculture Society, among many others.
pb@purdue.edu

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