Probiotics inhibit growth of coldwater disease bacteria

By SEAN ELLIS

Capital Press

HAGERMAN, Idaho -- University of Idaho researchers are studying a way to use "good bacteria" from the guts of fish to combat outbreaks of coldwater disease, the No. 1 cause of mortality among commercial rainbow trout in Idaho.

Researchers at UI's Aquaculture Research Institute have shown that probiotics mixed with fish feed result in a significant reduction in fish mortality due to coldwater disease.

Idaho produces about 41 million pounds of rainbow trout each year, about 75 percent of total U.S. production.

"We're excited about the research," said Professor Ken Cain, who leads the university's trout research. "We've seen very encouraging results in the lab that have been backed up by good results in the field."

Probiotics are live microorganisms such as bacteria that are similar to beneficial organisms naturally found in the gastrointestinal tract. They are used in dietary supplements and other food to provide health benefits to humans.

But probiotics for fish is an extremely new field, said Cain, associate director of the institute.

The state's $40 million commercial trout industry loses about $10 million each year to coldwater disease, and aquaculture facilities are particularly interested in the research.

"It's a disease we would definitely like to get control of and minimize its effects," said Randy MacMillan, vice president of research for Clear Springs Foods, the largest rainbow trout producer in North America. "The disease is a significant challenge."

The research could also benefit state and federal steelhead and salmon hatcheries in the Pacific Northwest that are impacted by coldwater disease.

UI researchers isolated 318 different types of bacteria from the guts of trout collected around the state. They were screened for their ability to inhibit the growth of the bacteria that cause coldwater disease.

Researchers then experimented with a couple of dozen in the lab by mixing them with regular fish feed. Two strains of probiotics emerged as the most promising for being able to reduce outbreaks of coldwater disease, and one has been tested in a field trial at a Utah Division of Wildlife Resources hatchery.

Fish fed the probiotics at the hatchery experienced as much as a 50 percent reduction in mortality due to coldwater disease.

"One strain's been pretty much evaluated in the lab and field tests," Cain said. "The other one needs additional trials in the lab and field."

The university has filed a patent application for the two strains of probiotics.

MacMillan said one big challenge of the study will be finding an economical way to mix the probiotics with regular fish feed.

"This early in the game, we don't know if it will be cost-effective to do that," he said. "We certainly welcome Ken's work and encourage him to continue it. It is certainly an encouraging avenue to pursue."

Cain said the team still needs to determine the best way to grow the probiotics on a large scale, store and ship them either directly to aquaculture facilities or feed mills.

The research team is looking at either developing a startup company to bring the product to market or collaborating with a company.

A $34,000 grant from the State Board of Education's Higher Education Research Council will help the researchers navigate the initial steps of developing the products for commercialization.

Cain's team is also researching ways to enhance a vaccine for coldwater disease. He believes using a vaccine in tandem with the probiotics may prove the best way to combat the disease.