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Think Tank: Fit for a fish

Scientists research fishmeal alternatives in fish feed

Scientists expect the bulk of a farmed fish's diet
    will come from plants in the future. - Photo Skretting
By Lauren Kramer
January 01, 2010

There's a long-standing perception that because most fish are carnivores, fishmeal is an imperative part of a farmed fish's diet. But that's not true, says Michael Rust, research biologist at the Northwest Fisheries Science Centre. Rust is developing an interagency white paper this month to discuss alternative aquaculture feeds that reduce or eliminate fishmeal and fish oil.

Rust says there are at least a dozen different research projects under way in the United States alone, with biologists looking at alternative proteins for farming different seafood species such as Atlantic and Pacific salmon, rainbow trout and others. The research projects include seaweed, insect meals, plant proteins and lipids, by-products from 
rendering terrestrial animals and fish scraps, even beer sludge and the by-products from ethanol are making a name for themselves as a possible fishmeal substitutes.

A blend of one of the plant meals looks to be the most promising fishmeal substitute. "Plant oils will provide the bulk of the protein and lipids, with seafood trimmings to provide a few of the required nutrients not contained in the plants. But I don't see any single item being a full replacement for fishmeal," he says. "Meal made from seafood trimmings is fully nutritional, but there is not enough of it to fully satisfy demand."

Rust just finished a study wherein the fishmeal portion of the diet of black sea bass was replaced by worm meal. "The fish ate it and liked it," Rust says. "But we haven't done a full-scale trial on it yet, and it's still a ways from being economically viable."

Meal worms cost $100,000 per ton and are comprised of 40 percent protein and 20 percent lipids. Fishmeal costs $1,400 per ton and contains 65 percent proteins and 3 percent lipids, while fish oil costs $2,000 per ton. "Both fish products are getting more expensive over time, but meal worms are currently not cost effective," says Rust.

That's because the majority of meal worms are fed to pet birds, and the process of drying and packaging the worms is expensive. "But if a small amount of worm meal can enable higher uses of cheaper plant-based proteins, then it might have a future in feeds for fish," he says.

For the past six years Rick Barrows, lead scientist and nutritionist at the U.S. Department of Agriculture's Agricultural Research Service, has been studying the replacement of fishmeal with plant ingredients including soy, corn, barley and wheat in feeds for rainbow trout.

"We've completely replaced fishmeal with plant ingredients and for a year now it's been used by rainbow trout producers on the West Coast," says Barrows.

But the plant ingredient-based diet is still more expensive than its fishmeal equivalent. In part, that's because Barrows and his team have been using food-grade plant ingredients and still need to find feed-grade resources. They are also trying to make it more cost effective by substituting animal products where applicable.

The findings gleaned from rainbow trout can be applied to other seafood species, but "nutritionally speaking, each species seems to have its own particular twist," he says.

Other fishmeal replacement studies are ongoing with Atlantic salmon at the USDA's National Cold Water Marine Aquaculture Center in Franklin, Maine, and with yellowtail and white sea bass in San Diego, in collaboration with the Hubbs SeaWorld 
Research Institute.

"In San Diego we're six weeks into a study where white sea bass have been fed a plant-based diet and they are showing better growth than when they are fed a fishmeal diet," says Barrows. "That's very close to proving the concept that you don't need fishmeal for a carnivorous marine fish."

When it comes to replacing fish oil in fish feed, no viable substitute has yet been found, though Barrows says algae oil "seems to have a lot of potential. We're doing a lot of work with biofuel companies to see if we can find a source of oil through them."

Meanwhile, Rust is leading an effort coordinated by the National Oceanic and Atmospheric Administration and the USDA to find out what research and technology transfer is necessary to increase the amount of non-fish ingredients in fish feed.

"One thing we'd expect is that in the future the bulk of a diet for farmed fish will come from plants," he says. "Fish trimmings or oil will be added just for specific nutrients or for flavor that is lacking in plants."

 

Contributing Editor Lauren Kramer lives in British Columbia 

 

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