TWIN FALLS • Feeding trout a diet that doesn’t include fish meal has long been the goal of fish nutritionists. That day is finally near.

“We are showing that you can grow fish without fish meal and we’re doing it at a lower protein level,” said Gary Fornshell, University of Idaho extension aquaculture educator.

Fornshell was part of a three-year, multi-state integrated research effort that focused on identifying alternative protein sources for trout, through feed formulation and all the way to evaluating the quality of the product for consumers.

Finding alternatives for fish meal has been a priority for aquaculture in part because fish meal costs have risen sharply over the last two decades and in part because consumers want to purchase more sustainable products.

Fish meal increased from about $750 a ton 20 years ago to more than $2,100 a ton last winter. Prices have settled back under $2,000 a ton again, but that’s still quite an expense. In the old days, diets were formulated to include around 40 percent fish meal. That’s expected to drop to as little as 10 percent industry-wide by 2020.

But research presented at the 2013 Idaho Aquaculture Association annual meeting showed that fish meal can be reduced to as little as 5 percent in salmon diets as long as the rest of the diet is balanced to meet the amino-acid needs of the fish.

Several presentations focused on the three-year Western Regional Aquaculture Center study that Fornshell was part of. The project began by identifying alternative or novel feed ingredients that had been used in other feed trials. From that information, two best experimental diets were formulated: one a plant product-based diet and the other an animal product-based diet.

The two experimental diets were compared with a traditional fish meal diet in both laboratory studies and a production facility.

“The production trial validated what we found in the lab,” Fornshell said. “All plant-based feed and animal protein feed without fish meal performed equal to the fish meal control feed.”

A second phase of the production trial will be run this summer.

Amino Acids Are Key

Chris Myrick, a fish physiologist at Colorado State University, focused on lysine levels during part of the laboratory trials. Lysine is one of the first three limiting amino acids in fish production. Lysine is typically high in fish meal diets, but not plant-based diets. But he found that lysine levels can be as low as 3 to 3.5 percent as long as the rest of the diet is very carefully formulated.

That’s an important finding when it comes to protein retention, a standard that is becoming almost as critical as feed conversion when talking about fish diets. Retaining more protein means better growth rate for the fish and a more economical feed conversion for producers. Higher protein retention means less nitrogen in the waste generated by fish, which means better water quality below fish production facilities.

Gibson Gaylord, a physiologist nutritionist with the U.S. Fish and Wildlife Service in Bozeman, Mont., said one of the benefits of this research project is the flexibility it offers to producers. He worked on digestibility studies that helped refine the lysine levels used in diets that Myrick fed in the lab trials and Fornshell fed in the production trials.

“We had refined the diets in the lab so we were pretty confident when they went to the production trial,” Gibson said. Still, he was pleased to see that the production trial showed no difference in yield or dress out between the diets.

Even though there is no difference between the diets when it comes to fish gain, the plant-based diet did have an effect on white trout production. The plant-based diet included 22 percent corn gluten meal, which gave white trout filets a yellow color. That could be an issue for consumers if the yellow filets were marketed in a case next to red trout filets.

Two of the three fish processors in the Magic Valley handle only white trout so it is a concern here. But, as Fornshell points out, the animal-product based diet performed equally well so producers have options. The plant-based diet was also more expensive than the animal product diet.

Consumers Don’t Have Strong Taste

Carolyn Ross, an assistant professor in food science at Washington State University, has conducted two years of sensory evaluations that found consumers didn’t have a strong preference for fish produced on one diet over another.

She conducted paired evaluations in which consumers were given two filets and asked questions such as: Which filet is firmer? Which has a more fishy taste? She used special lights to disguise any color differences between the filets.

Overall, Ross found that if the diet contained animal products, consumers said it had a more “grassy” flavor. Fish fed the fish meal diet tasted more “fishy.”

“That’s very intuitive,” Ross admitted, “but to find it in comparison-after-comparison, year-after-year, taste test-after taste-test was validating.” Especially considering how variable fish are from raceway to raceway.

The research also supported other findings in the food science industry: That there is no perfect product for everyone.

“Different people like different products,” she explained. “Some people like a filet that is fishy and flaky, some people will like a more mild-flavored product and firm. That doesn’t mean one product is bad, they are just different. The food science industry is getting away from one product for everyone.”

And that’s good news for an industry that is discovering that there is not one perfect ingredient that will work to replace fish meal in all diets, but it is still possible to raise fish without any fish meal.

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