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Can Farmed Trout Go Vegetarian?

A key ingredient in the commercial feed that fish farmers buy is other fish caught in the wild. Northwest trout farmers - and some salmon growers - recognize this practice is unsustainable, so the search is on for a cost-effective alternative fish food.

But trout are carnivores. They can't just become vegetarians, or can they? And would seafood consumers be able to notice any difference?

Tasting the difference

I'm one of 72 volunteers recruited as taste testers at a trout fillet tasting panel. We're at the School of Food Science at Washington State University in Pullman. I'm seated - fork at the ready - in a row of booths - kind of like 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 these trout samples that I'm being presented because one was raised on fish meal, another on animal proteins and a third on a mostly vegetarian diet.

The first sample has a pretty classic trout flavor. These have been poached. There's no sauce on them. So you get pure, unadulterated trout. And I couldn't really tell you if that was raised on fish, land animals... or vegetables.

I compare 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. Professor Carolyn Ross supervises the taste testing. She's been serving panelists trout raised on different feeds since 2008.

"I think they are getting close. Certainly, there are differences between samples. But whether that is a game changer or not is a different question," Ross says. " 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."

Byproducts, corn and insect larvae

Idaho is by far the No. 1 trout producing state in the nation. A longtime fish grower there says finding a cost-effective alternative feed is the industry's "No. 1" 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 says. "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.

But Ray doubts going completely vegetarian is the answer. "We have healthier fish if we put a little bit of fish meal in the diet. 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."

A magic formula?

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 8th. There, fish farmers will get their own chance to nibble the various trout fillets we sampled.

U.S. Fish and Wildlife Service scientist Wendy Sealey leads the multi-agency study of trout dietary treatments. She is based at the Bozeman Fish Technology Center. "It goes beyond trout," observed Sealey. "It applies to other aquaculture species."

Parallel studies are testing alternative feeds for farmed Atlantic salmon, coho 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.

On the Web:

Alternative Protein Diets for Rainbow Trout - Western Regional Aquaculture Center
Trout-Grains Project - USDA Agricultural Research Service 
Sensory evaluation lab - WSU School of Food Science 
"Seafood Watch" sustainability assessment of farmed trout - Monterey Bay Aquarium

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