In recent months, the buzz has been about using various fractions from DDGS as protein ingredients in feeds for the aquaculture industry.  Indeed, there are some very interesting value-added ingredients coming down the pipeline. Unbeknownst to many, however, traditional DDGS has already been proven time and again as working very well as a protein source in a variety of aquafeeds. As with any feed ingredient, though, it must be used at the proper level, and in proper combination with other ingredients as part of a complete, balanced diet. Formulations vary, depending upon the species and the age of the fish—similar to any other livestock species. A broad look at the industry and a bit of history are in order.

Aquaculture is the fastest growing animal food-producing sector globally. The industry has been growing by nearly 7 percent per year for almost 40 years. In fact, it has been the only food producing sector growing at a rate greater than human population growth. Most of this growth has been outside the U.S. and, although there is considerable potential here in the U.S. for fish production, it has been slow to materialize. China has by far been the world’s leader in aquaculture production, but other countries around the world have also become large players, including Indonesia, Vietnam, Bangladesh and several South American countries. Even though many countries have rapidly increased production during the past decade, China is still the largest producer of fish.

For a typical fish production operation, in the U.S. or abroad, feed costs represent between 40 and 70 percent of all operating costs, depending on the specific farm. Historically, fish meal has been one of the most important ingredients in aquatic diets, supplying essential proteins, amino acids, fatty acids, minerals and other nutrients. In recent years, as the demand for fish meal has grown in tandem with the growth of aquaculture, the price of fish meal has skyrocketed, hovering between $1,500 and $2,000 per metric ton for the past four years. The increases in both demand and price have propelled the search for wild marine and fisheries stocks, even though wild capture has not increased significantly for many years.

A logical solution to this dilemma is to use plant-based cereal and oilseed ingredients. There are many to choose from. There are also challenges with many of these alternatives, however, including unwanted nutrients and antinutritional factors (e.g., trypsin inhibitors, protease inhibitors, lectins, gossypol), nutrient variability, poor nutrient balances (e.g., amino acid profiles, fatty acid profiles), cost-intensive processing to convert them into usable form, low-volume production and poor effectiveness in fish performance. At the moment, soy-based ingredients are the leading contenders for fish meal replacement.

DDGS is also an effective protein source for aquaculture feeds. Advantages include its wide availability, moderate protein level, complementary amino acid profile (depending on supplementary ingredients), and effectiveness in many fish species when used in proper conjunction with other ingredients. The greatest advantage, however, is that DDGS is generally one-tenth to one-twentieth the price of fish meal, and approximately one-half the price of soybean meal. The economics are hard to argue with.

Many feeding trials have investigated the use of DDGS in aquafeeds over the years. In fact, the Distillers Grains Technology Council funded the first feeding trials as far back as the 1950s, and found that distillers dried solubles could be effectively used in catfish and rainbow trout diets up to 21 percent inclusion levels. Most early aquaculture research used DDGS from beverage distilleries, because the fuel ethanol industry was so small back then. But, the idea gained traction in the 1990s and 2000s as the fuel ethanol industry grew, and the quantity of DDGS grew. Some of the landmark studies, listed in the accompanying table, found DDGS (or even thin stillage or solubles in some cases) can be successfully used in a variety of fish diets, with fairly high inclusion levels.

The economics of using DDGS to partially offset fish meal are quite astounding. For example, if fish meal were used in an aquafeed at 40 percent inclusion, and DDGS increasingly replaced that fishmeal (from 0 to 100 percent), the relative cost of the diet would decrease, as shown in the accompanying graph. At 100 percent fish meal replacement, the total diet cost would be reduced by almost 90 percent. Overlaid on this graph, I also show some of my research team’s results over the past decade. Depending on the species and the other ingredients used, we successfully used 20 percent DDGS inclusion in tilapia diets with no difference compared to a fish meal-based control diet; we have been able to use up to 40 percent DDGS in yellow perch diets, and we have even been able to achieve up to 60 percent DDGS inclusion in rainbow trout diets. All of these studies were conducted using traditional DDGS, not fractionated products.

Using DDGS in aquafeeds is not quite a slam dunk, however. Some of the challenges associated with using DDGS include both feed manufacturing as well as fish performance considerations. In terms of processing, the big question is how much DDGS can be used in a formulation without hindering the extrusion process or sacrificing pellet quality. We need to have cohesive, stable, floating pellets. This can be achieved with high levels of DDGS, but there is an art in operating the extruder so that high quality pellets can be produced. In terms of feeding trials, we need to determine how much DDGS the fish can eat, what level will result in optimal fish growth and feed conversion, what else must be added to the ingredient matrix, and what level will result in optimized production costs. In terms of feeding recommendations, it appears that using 20 percent DDGS inclusion is about optimal, both for feed manufacturing operations, as well as fish performance (this is true for many fish species, actually). And this has been borne out by much research in the past decade, both by my team as well as other researchers.

DDGS is a viable protein ingredient for aquafeeds when used as one component of a balanced feed. We need to convince aquaculture producers as well as aquafeed manufacturers that real economic benefits can be realized by using DDGS as a protein source, and feed quality and fish performance will not suffer if done correctly.

Author: Kurt A. Rosentrater
Executive Director,
Distillers Grains Technology Council
515-294-4019
karosent@iastate.edu