State euthanizes 30,000 Atlantic salmon sickened at Michigan hatchery

(FOX 2) - The state euthanized tens of thousands of salmon that had been grown in one of its hatcheries after it was unable to treat an outbreak of kidney disease in the fish, the Michigan Department of Natural Resources said Tuesday.

More than 31,000 Atlantic salmon were humanely killed after it was discovered the fish being reared at the Harrietta State Fish Hatchery in northern Michigan had been infected with bacterial kidney disease.

BKD is fatal to trout and salmon and is believed to be responsible for the large declines of Great Lakes Chinook salmon populations in the mid-1980s. BKD is caused by the Renibacterium salmoninarum bacteria.

It was found during an inspection of fish in early April at the Wexford County hatchery. Staff at an animal health lab at Michigan State University confirmed the presence of the problematic bacteria that causes BKD.

Officials attempted to save the salmon with a month-long antibiotic treatment, but it was not effective in eliminating the infection.

"These fish were sick enough that a significant portion of the fish were not feeding well," Aaron Switzer, DNR fish production program manager said. "That means that the antibiotic, which was mixed in with their feed, was not being eaten at the rate necessary to eliminate the pathogen."

Ed Eisch, assistant chief at the DNR's fisheries division said the disease is a Level 1 restricted pathogen. Fish that test positive for any pathogens at that level can still be stocked as long as they're free of disease.

The event is extremely uncommon, he said, and has only happened about three times in the decades he's been at the DNR.

It's unclear how the bacteria got into the hatchery, but he suspects the source was brown trout eggs that shed the bacteria. While many native fish species are resistant to illnesses, Atlantic salmon are particularly sensitive to bacteria.

"Atlantics are susceptible to everything. So if there's a pathogen there, they're going to get sick," he said.

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The other hatchery that rears Atlantic salmon is the Platte River State Fish Hatchery, which is near Traverse City. That population was healthy and helped stock tens of thousands of fish in Torch Lake, the Au Sable River, the Thunder Bay River, and in Lexington Harbor in Lake Huron.

Another 27,000 fish will also be added to the St. Mary's River and Sault Ste. Marie this week.

"Having to make the decision to dispose of these diseased fish hurt, but it was clearly the right thing to do," said Eisch. "The Atlantic salmon fishery is highly valued, but first and foremost, we have a public trust responsibility to protect the aquatic resources of the state of Michigan. Stocking fish known to be actively suffering a disease outbreak would be counter to that."