More than 31,000 Atlantic salmon raised at a Michigan fish farm had to be killed after they failed to recover from the disease, officials said Tuesday.
The decision followed a failed 28-day treatment period at the Harrietta Hatchery in Wexford County in northwestern Michigan.
“It was painful to make the decision to discard these sick fish, but it was clearly the right decision,” Ed Eisch, assistant chief of the DNR Fisheries Division, said in a statement. “The Atlantic salmon fishery is highly valued, but first and foremost, we have a public responsibility to protect the aquatic resources of the state of Michigan. Restocking fish known to be actively suffering from a disease outbreak would go against that.”
The fish, about 6 inches long, were loaded into a truck Monday, euthanized with carbon dioxide and buried in a pit, Eisch said.
The salmon, sick with bacterial kidney disease, were treated with medicated feed.
“The bacterium that causes bacterial kidney disease is listed as a Level 1 restricted pathogen in the Great Lakes Fish Health Management Model Program,” Eisch said. “Fish positive for pathogens under Level 1 restriction can be released into areas where the pathogen is already known to exist, but only if they are free of signs of disease. This batch of fish is still showing signs of active BKD, so they cannot be turned off.” The unhealthy fish would have posed a risk to other fish if released into Michigan waters, he said.
The disease probably came from the brown trout in the hatchery.
“We think there are some latent bacteria in the brown trout, and they released the bacteria, enough that the Atlantics picked it up and got sick from it,” Eisch said.
Officials say BKD causes salmon and trout deaths and played a major role in the decline of Chinook salmon populations in the Great Lakes in the mid-1980s.
The DNR says it keeps 20 to 30 million fish in Michigan’s public waters each year. Healthy Atlantic salmon from Platte River State Fish Hatchery were released into Torch Lake, the Au Sable and Thunder Bay rivers, and Lexington Harbor in Lake Huron. The St. Marys River in Sault Ste. Marie also received almost 27,000 fish this week.
Scientists at Michigan State University plan to develop a vaccine to protect fish from future outbreaks, Eisch said.
