By CAROL RYAN DUMAS
TWIN FALLS, Idaho -- Finding an alternative for fish meal in fish feed is a high priority for the aquaculture industry, and collaborative research on fish diets looks promising, researchers say.
Lab and commercial production trials have shown that rainbow trout fed either a plant-based or animal-based protein diet (without fish meal) show no statistical differences from trout fed a typical commercial feed containing fish meal.
In addition, the alternative diets supported equal growth at 38 percent digestible protein, compared with the typical 45 percent crude protein in standard commercial feed.
The findings are exciting because fish meal is a finite resource. There's a limited supply and high demand, which makes it expensive, said Gary Fornshell, University of Idaho extension aquaculture specialist and a principal investigator on the project.
Fish meal prices have more than doubled since 2007 from their 30-year average range of $400 to $850 a metric ton to an average of nearly $1,900 per metric for the first four months of this year.
The research on alternative diets was presented June 8 at the Idaho Aquaculture Association's annual meeting in Twin Falls.
In laboratory trials, the alternative diets and lower protein levels did not compromise body condition, growth, efficiency, or survival, said Wendy Sealey, a physiologist nutritionist at the U.S. Fish and Wildlife Service's Bozeman Fish Technology Center and a principle investigator on the project.
And no real differences were seen in feed conversion or filet ratio, she said.
Those findings were repeated in commercial production trials in ponds owned by SeaPac of Idaho in Twin Falls County, Fornshell said.
Fish on the alternative diets performed equal to those on the control diet with no statistical differences, he said.
"The bottom line is fish meal is not an essential nutrient. It's a very good ingredient but not an essential nutrient," he said.
The researchers did find one potentially negative difference and that was in pigmentation of the fish fed the plant-based protein diet. Filets of those fish would be yellow and unmarketable, due to the corn gluten, Fornshell said.
For the trials, the researchers added pigment to the feed to result in a red filet, a practice that is done in farmed salmon production and in some trout production. But filets from the fish fed the plant-based diet were paler and more orange rather than red.
At the levels fed, corn gluten won't work for Idaho's primarily white flesh production. White corn meal gluten does exist but is not readily available. Other researchers are also looking at removing the pigment from yellow corn meal gluten, he said.
Protein in the plant-based diet came mostly from corn gluten but also from soy isolate or soy protein concentrate, soybean meal and whole wheat. Protein in the animal-based diet came from pet-grade poultry byproduct. Both diets were supplemented with amino acids, Fornshell said.
Cost figures of the alternative feeds are preliminary but Fornshell did analyze returns over estimated feed costs Those returns for mid-range priced feed at normal feed conversion rates were 42.5 cents per pound of fish for the plant-based diet, 46.3 cents for the animal-based diet without fish meal, and 46.2 cents for the commercial diet containing fish meal.
The results are exciting because they demonstrate alternative diets are doable; fish performed well on both diets. And the plant-based diet uses readily available commodities wile the animal-based diet without fish meal doesn't have the potential pigmentation problem, he said.
Due to disease and mortality problems associated with the older ponds' design in the commercial production trial, another trial will be conducted, followed by an economic analysis, Fornshell said.
The three-year, $360,000 research project is funded by the Western Regional Aquaculture Center, with considerable in-kind support from industry. Washington State University, Colorado State University and USDA Agricultural Research Service are also involved in the research.