HARRIETTA, Mich. – The Michigan Department of Natural Resources said that fisheries staff had to kill just over 31,000 Atlantic salmon that were sick with bacterial kidney disease (BKD).
The disease was found in early April during routine prestocking inspection of fish at the Harrietta State Fish Hatchery in Wexford County. Staff at the Michigan State University Aquatic Animal Health Lab noticed signs of the disease and confirmed the presence of Renibacterium salmoninarum, the bacterium that causes BKD.
BKD is a bacterial disease that is known to kill trout and salmon. It is believed to be the cause of the decline in Great Lakes Chinook salmon populations in the mid-1980s.
“The bacteria that causes bacterial kidney disease is listed as a Level 1 restricted pathogen in the Model Program for Fish Health Management in the Great Lakes,” said Ed Eisch, DNR Fisheries Division Assistant Chief Ed Eisch. “Fish that are positive for Level 1 restricted pathogens can be stocked where the pathogen is already known to exist, but only if they are free of signs of disease. This lot of fish still shows signs of active BKD so they cannot be stocked.”
The salmon at the Harrietta State Fish Hatchery were given a 28-day antibiotic treatment that was completed on May 17, but the treatment didn’t completely get rid of the infection. After treatment, a group of fish were sent to the lab and internal signs of active disease were still found.
“Having to make the decision to dispose of these diseased fish hurt, but it was clearly the right thing to do,” Eisch said. “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.”
Aaron Switzer, DNR Fish Production Program manager, said it’s not surprising that the treatment wasn’t completely successful.
“These fish were sick enough that a significant portion of the fish were not feeding well,” Switzer 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.”
The Harrietta State Fish Hatchery is not the only DNR hatchery rearing Atlantic salmon. There were salmon raised at the Platte River State Fish Hatchery, which is about 15 miles west of Traverse City. Those fish were deemed healthy and were stocked in four places:
- Torch Lake received 15,883 fish.
- The Au Sable River in Oscoda and the Thunder Bay River in Alpena each received 25,000 fish.
- Lake Huron’s Lexington Harbor received 40,000 fish.
the St. Marys River at Sault Ste. Marie will receive just under 27,000 fish.
The DNR stocks 20 million to 30 million fish each year into Michigan’s public waters.
Michigan’s hatchery system is getting infrastructure updates to fix a backlog of maintenance needs. Some of the upgrades will improve biosecurity, which is expected to help protect the fish from illnesses like BKD.
You can learn more about fish and aquatic diseases at Michigan.gov/FishHealth. You can learn more about the DNR’s fish production program and hatcheries and weirs at Michigan.gov/Hatcheries.