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Farmed trout go vegetarian (sort of), but what about the taste?

Tom Banse

The search is on for a cost-effective alternative fish food in the form of pellets. A key ingredient in commercial feed is other fish caught in the wild. Northwest trout farmers and some salmon growers recognize the practice is unsustainable.

But trout are carnivores; they can't just become vegetarians, or can they? Washington State University recently held a taste test to see if seafood consumers can tell any difference.

Put to the test: Difference in taste?

I was one of 72 volunteer taste-testers at WSU’s School of Food Science in Pullman. I was seated, fork at the ready, in a row of booths that resembled voting booths but with sliding windows to the test kitchen.

If it's true that you are what you eat, I should be able to tell the difference between the trout sample raised on fish meal, another on animal proteins, and a third raised on a mostly vegetarian diet. The fish have no sauce to allow tasters to sample pure, unadulterated trout. 

I couldn't really tell whether each sample had been raised on fish, land animals, or vegetables.

I compared notes later with some of my fellow testers. Some got a little bit of "grassy" flavor from what turned out to be the vegetarian-fed trout fillet. The trout raised on traditional fish meal had slightly more "fishy" flavor and aroma. The trout that ate chicken byproducts did not taste like chicken.

The definition of success in this aquaculture experiment would be for the non-fish alternative diets to work out more or less the same as the current fish-based feed.

"I think they are getting close,” said WSU professor Carolyn Ross, who supervises the taste testing. “Certainly, there are differences between samples. But whether that is a game changer or not is a different question. So yes, I can tell one has a more fishy aroma. I can tell one is firmer. But if you're sitting down at home having a BBQ, it's not going to make a big difference."

‘We knew this was coming’

Idaho is by far the top trout-producing state in the nation. A longtime fish grower there says finding a cost-effective alternative feed is the industry's "number one" priority. Leo Ray of Buhl, Idaho says fish meal used to cost around $300 per ton about 15 years ago. Nowadays, the same amount runs him close to $2,000.

"We knew this was coming,” Ray said. “There is a limit on the amount of fish meal the ocean can produce, and we've hit that limit."

Ray says the suppliers he buys from have already reduced the wild fish content in commercial feeds somewhat. He and his competitors in southern Idaho have tested all sorts of alternative diets. They've fed their fish poultry byproducts, corn and soybean protein, coconut oil, and ground-up insect larvae, to name a few. Ray doubts going completely vegetarian is the answer.

"We have healthier fish if we put a little bit of fish meal in the diet.” Ray said. “I think what we will end up with is a diet that instead of using 20 or 30 percent fish meal, will be using 5 percent fish meal."

University of Idaho Extension educator Gary Fornshell says an upcoming economic analysis could shed more light on what the ultimate formulation of trout feed will be. Federal government and university researchers are scheduled to present their findings to an industry gathering in Twin Falls on June 8. There, fish farmers will get their own chance to nibble the various trout fillets.

Beyond trout

"It goes beyond trout," said U.S. Fish and Wildlife Service scientist Wendy Sealey, who leads the multi-agency study of trout dietary treatments. "It applies to other aquaculture species."

Parallel studies are testing alternative feeds for farmed Atlantic salmon and several species of warm water fish. 

"Salmon are harder to wean off fish meal," said Ray, while tilapia could fairly easily be converted to a plant-based diet.

Tom Banse covers national news, business, science, public policy, Olympic sports and human interest stories from across the Northwest. He reports from well known and out–of–the–way places in the region where important, amusing, touching, or outrageous events are unfolding. Tom's stories can be found online and heard on-air during "Morning Edition" and "All Things Considered" on NPR stations in Washington, Oregon, and Idaho.