Co-products of the United States biofuels industry as alternative feed ingredients for aquaculture

The tremendous growth of the biofuels industry has made large amounts of co-products (i.e. distillers grain and crude glycerin) available for use in aquafeeds. This chapter reviews the prospects and challenges associated with their use in aquafeeds. Properties of each product as it pertains to fish nutrition and available research are described for different fish species. Despite the apparent deficiency in lysine and the high fibre content in DDGS, considerable amounts of DDGS can be fed to omnivorous fish species without impact on growth or product quality. Nutrient variability is, however, an issue that needs to be considered when feeding DDGS to fish. The use of crude glycerin in fish is less clear, and further research is necessary before nutritional recommendations can be made. Biofuel co-products as livestock feed – Opportunities and challenges 404 and fish oil. Fish meal used in aquaculture represented 68.2 percent of total global fish meal production in 2006 (Tacon and Metian, 2008), but increased pressure due to exploiting marine resources and rising prices could ultimately decrease the use of fish meal, as it will inevitably be replaced by less expensive alternative proteins. DDGS, a relatively cheap protein source (Figure 3) compared with fish meal, is a candidate plant protein. During the last 10 years, DDGS market price has been generally between 5 percent and 20 percent that of fish meal. While DDGS is not recommended as a direct, complete replacement for fish meal, it can be used with, or in lieu of, other plant proteins (such as soybean meal – SBM) to reduce the use of fish meal in aquafeeds. As shown in Figure 3, over the last decade the price of DDGS has ranged from approximately 20 percent to 70 percent that of SBM. This chapter will review the nutrient composition of major biofuels (i.e. maize-based fuel ethanol and soy-based biodiesel) co-products (i.e. distillers grain and crude glycerin), will provide summaries of available nutritional studies for different fish species, and will conclude with final remarks on challenges associated with these co-products and areas of needed research. Before proceeding, however, it is important to note a few key issues. First, maize is the primary feedstock for fuel ethanol production in the United States. Other starch-rich materials can theoretically also be used to produce ethanol, including barley, cassava, field peas, millet, triticale, oats, rice, rye, sorghum, sweet potato and wheat. Unfortunately, most of these alternative starch sources have only been investigated on a laboratoryor pilot-scale and are not readily commercially available. Not surprisingly, fish feeding trials are essentially non-existent for co-products from these substrates, and thus will not be discussed in this chapter. In contrast, biodiesel can be produced from a variety of oilseeds and lipid-containing materials, including canola • DDGS from fuel ethanol production can be an effective protein ingredient in aquafeeds. • DDGS serves to replace SBM and maize in the diet, but