HAGERMAN, Idaho — With world demand for farmed fish growing by about 8% a year, a commonly used feed will become harder to get and more expensive.

Fish meal is made from small ocean fish such as menhaden, sardines and anchovies. Since those populations are limited, so too is the future supply for the aquaculture industry, said University of Idaho aquaculture researcher Matt Powell. In addition, using one fish to feed another can be a public-perception problem.

Soybean meal is an economically and environmentally sustainable solution for the trout-production industry in the state’s south-central region.

But soybean meal comes with its own challenges for trout. It has potentially harmful components, such as saponins and lectins, that cause distal enteritis — similar to irritable bowel syndrome and Crohn’s Disease in people, Powell said.

“Soybeans are abundant and cheap, but they need to be processed to get the protein fraction out of them,” he said, adding that expense increases with every production step.

“We have developed a rainbow trout that eats an all-plant diet and grows just as fast as rainbow trout that are fed a conventional fish meal diet,” Powell said.

After some 22 years of working together, UI and USDA researchers are on the 12th two-year generation of rainbow trout that they genetically selected — without adding genes — to thrive on soybean meal. Selection is overseen by Ken Overturf of the USDA Agricultural Research Service.

For about eight years, genetics for a vegetarian rainbow trout, known as the USDA-UI strain, have been released to the industry.

A key focus of Powell’s research is to “figure out how these fish are tolerant to soybean meal,” he said. “Our trick is to select rainbow trout that can eat minimally processed soybean meal.”

He looks at “how they are able to digest that, recognize it as food and not have a reaction to it,” he said.

The immune systems of the fish have changed over the generations as researchers increased their intake of minimally processed soybeans meal. Now they can feed on it without getting enteritis, Powell said.

In the industry, pelleted diets contain a bit of soybean meal.

“You can’t give them too much because it will give them enteritis,” Powell said. “What we have shown is you can select for tolerance to soybean meal in the diet.”

Breeding in general has gotten more efficient, as some lines of fish selected can grow to a pound in about six months, down from a year or so in the mid-1990s, he said.

“The fish now are just so good at what they do,” Powell said.

Another goal for the team is to reduce effluent from fish farms that are home to the rainbow trout that eat a plant-based diet.

The researchers are incorporating binders, for example.

“The idea is to keep the phosphorous and nitrogen and whatnot bound to the fecal pellet, rather than dissolving into the water, so the water remains cleaner,” Powell said, as pellets stick to the raceway surface and are removed.

Matt Powell

Title: professor, University of Idaho Aquaculture Research Institute. Based at Hagerman Fish Culture Experiment Station.

Age: 59

Education: B.S. and M.S. in geology, University of Idaho; Ph.D., geology, Texas Tech; postdoctoral research in fisheries genetics, UI.

Hometown: Mountain Home, Idaho. Lives in Twin Falls.

Family: Wife Chris Vaage, recently retired from Idaho State University; adult son.

Hobbies: hunting, bird dogs, fly fishing, outdoor writing

Affiliations: Western Regional Aquaculture Center technical subcommittee, Ocean Resources Enhancement and Hatchery Program (California) science advisory committee