Research aims to reduce rainbow trout losses in U.S. hatcheries

Michigan State University is trying to reduce rainbow trout losses in U.S. hatcheries caused by the yellow-pigmented bacterium, Flavobacterium psychrophilum.

Chris with Rainbow Trout Experiment-resized
Michigan State University doctoral student Christopher Knupp examines fish in a tank. Credit: Thomas Loch, Michigan State University
March 1, 2023

Rainbow trout are one of the most valuable finfish in the United States, valued at more than $200 million in 2021, according to USDA’s National Agricultural Statistics Service (NASS). Unfortunately, millions of rainbow trout are lost each year, mostly to disease, resulting in substantial economic losses. As a result, researchers at Michigan State University are trying to reduce rainbow trout losses in U.S. aquaculture facilities and hatcheries, specifically, losses caused by the yellow-pigmented bacterium, Flavobacterium psychrophilum.

F. psychrophilum spreads from fish to fish and from infected parents to offspring via infected reproductive fluids and eggs. It causes bacterial coldwater disease and rainbow trout fry syndrome in salmon and trout, which have led to substantial losses of farmed and hatchery-raised trout and salmon. Unfortunately, few FDA-approved treatment options for these diseases exist, and effective commercial vaccines are still unavailable in the United States.

“Over the past several years, we have determined that certain strains of F. psychrophilum seem more frequently linked to disease outbreaks in U.S. trout farms, may be better able to resist FDA-approved antimicrobial treatments, and may be more adept at persisting in fish farms and hatcheries,” said project director Thomas Loch, assistant professor at Michigan State University.

“Our findings also suggested that some strains are more difficult, or even impossible, to detect via widely used laboratory tests. Thus, this project aimed to develop methods for more rapidly and effectively detecting and diagnosing all recognized F. psychrophilum variants in the United States and better understand the mechanisms by which this bacterium persists and is transmitted in trout and salmon facilities,” Loch said.

As a result of funding from USDA’s National Institute of Food and Agriculture, Loch and his team have developed multiple methods to detect this very problematic bacterium, allowing for more timely disease diagnosis and treatment recommendations, therefore reducing losses. Moreover, their research has provided insights into how F. psychrophilum interacts with its fish host and aquaculture facility environment, which, in the short-term, can be used to inform best management practices to limit F. psychrophilum transmission, and, in the long-term, inform future research aimed at developing improved disease prevention and control strategies, including vaccine development.

The potential return on investment for this research is substantial. In 2021, the total value of trout sales was $97.3 million, but the total losses of trout intended for sale were $8.09 million, according to NASS. Disease accounted for 54% of these losses.

F. psychrophilum is believed to play a central role and can lead to losses of 70% in severe cases, which, if incurred in a single rearing unit of, for instance, 100,000 trout, would equate to 70,000 fish for a loss of $187,600, of course depending on the age of the affected fish. Considering some aquaculture facilities rear hundreds of thousands of trout at once, losses of this magnitude have a significant economic impact,” Loch said. “Fortunately, much of these losses can be mitigated through prevention, timely diagnosis and treatment, which our research directly contributes to. Moreover, our research uncovered how F. psychrophilum survives in its environment and is transmitted, which fuels disease outbreaks. Therefore, our research provides insights into how aquaculture facility personnel can most economically direct their efforts to reduce the risk of disease outbreaks.”