Maggots used to fatten rainbow trout

Cow manure and fish guts and maggots. It could all soon be dinner -- if you're an Idaho rainbow trout.

University of Idaho and Idaho State University scientists are working on a new maggot-based feed capable of fattening rainbows for the dinner table, while simultaneously helping slash growing mounds of manure and fish entrails.

Idaho is America's largest commercial producer of trout, with the industry bringing in more than $35 million annually. And with 500,000 cows, it's surpassed Pennsylvania as the nation's fourth-biggest dairy state.

That got Sophie St. Hilaire, an aquatic species veterinarian, thinking: Why couldn't dairies use a slurry of cow dung and trout intestines to grow maggots rich in fatty acids that make fish so good for humans?

With demand from giant Chinese fish farms driving fish meal prices up to $1,400 a ton, St. Hilaire is aiming to create something much cheaper that also eats up tons of cow dung and fish guts in the process.

“Don't laugh -- I've taken my kids to help me. My 3-year-old tells me, 'Maggots are gross.' Yeah, I say, but they're going to save the fishery,” she said. “We're making protein out of a waste product that's kind of a pain to manage.”

Black soldier flies, already used in Asia to eat restaurant waste, can reduce manure by 50 percent, turning it quickly to insect biomass. In fact, they're being studied in southern states including North Carolina, Georgia and Texas, whose big poultry and hog industries hope to harness the flies' voracious appetite for manure.

They're also a tropical species that can't survive Idaho's harsh winters, St. Hilaire said, making it unlikely adult flies that might escape could establish themselves and become pests. And though adult flies resemble wasps, they don't bite.

The work in Idaho is being done with a $120,000 grant from the U.S. Department of Agriculture's sustainable agricultural research program.

First, animal waste management engineer Ron Sheffield, of the University of Idaho, gathers manure in buckets, then seeds it with fly eggs imported from a commercial insect grower. He's gone through 700 gallons of manure so far.

About 70 days later, fish guts are added to the brew to help enrich the maggots with heart-healthy omega-3 and omega-6 fatty acids. The resulting maggots eventually wriggle up specially built ramps -- only to drop through holes into waiting buckets.

That's when Wendy Sealey, a University of Idaho fish nutritionist, gets involved: She washes the maggots, then freeze grinds them to be fed to rainbow trout in long runs at the test station along the Snake River.

The fish seem to have developed a taste for them.

“It makes sense to me that the black soldier flies are closer to their natural food than corn and soybean meal,” said Sheffield, an avid angler.

The next step is to raise fish to harvestable size, then enlist college students for blind taste tests to determine whether they are comparable in flavor and texture to trout raised on traditional commercial fish food. So far, the team's work has been so encouraging that they've enlisted a local dairy for a larger test in 2008.

Commercial fish food producers are intrigued, though they say there's no guarantee a marketable product will result.

Dairy farms would have to erect sizable facilities to raise the maggots. A distribution system must be developed. And after harvest, the maggots must be stored for long periods, then mixed seamlessly with other fish food ingredients in existing feed mills.

Mass maggot production will also be key, many said.

“There has to be a sufficient and regular supply, so that I can count on it,” said Richard Nelson, of Nelson & Sons, a fish-food producer in Murray, Utah. “You need volume production, to reduce the price. If I'm only adding half a pound of this, it's not worth it.”

In his laboratory in Twin Falls, waste engineer Sheffield said he's optimistic this could become a niche industry for the region's burgeoning dairies that now generate more than 10 billion gallons of milk products annually -- and 27 billion pounds of manure.

Still, he concedes working with manure, fish guts and squirming maggots isn't exactly a job for the faint of heart.

“Hey, you look at a five-gallon bucket of wigglies and see if your stomach doesn't do a summersault,” he said.

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Maggots used to fatten rainbow trout