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31,000 Killed Due to Bacterial Kidney Disease Outbreak in Salmon in the US

Bacterial Kidney Disease Outbreak in Salmon

United States: The Michigan Department of Natural Resources revealed on Tuesday morning that over 31,000 Atlantic salmon in Wexford County were culled following a positive test for bacterial kidney disease (BKD).

“Deciding to euthanize these infected fish was a difficult but necessary decision,” stated Ed Eisch, division assistant chief for DNR Fisheries, in a press release.

Bacterial kidney disease, a persistent infection caused by the bacterium Renibacterium salmoninarum, manifests through symptoms such as abdominal fluid accumulation, swelling, muscle ulcers, anemia, and blood blisters. The DNR attributes this disease to the decline of Great Lakes Chinook salmon populations in the mid-1980s, as per bridgemi.com.

The infection was detected during a routine inspection in early April at the Harrietta State Fish Hatchery in Wexford County and was confirmed by the Michigan State University Aquatic Animal Health Lab.

“The value of the Atlantic salmon fishery is immense, but our foremost responsibility is to safeguard Michigan’s aquatic resources. Releasing fish with an active disease outbreak would be irresponsible,” Eisch asserted.

Although a 28-day antibiotic regimen concluded on May 17, it proved insufficient, according to the DNR. Post-treatment, signs of active disease surfaced in another group of fish.

“The antibiotic treatment is generally effective when the bacterium is initially detected. However, since these fish had already contracted BKD, they exhibited increased resistance to the treatment,” Eisch explained to Bridge Michigan, as reported by bridgemi.com.

Over the past decade, occurrences of fish testing positive for bacterial kidney disease have been infrequent, although cases involving the bacterium Renibacterium salmoninarum have been more common, according to Eisch. Previously, such fish were successfully treated, but this situation was different.

“These fish were sufficiently ill that many were not consuming food properly,” said Aaron Switzer, DNR fish production program manager. “The antibiotic, mixed with their feed, wasn’t ingested at the rate required to eliminate the pathogen.”

Each year, the DNR stocks between 20 million and 30 million fish in state waters. By the fall of 2023, over 9 million individual fish had been stocked.

Infected fish were first observed in 1999 and have been identified in various waters across the Upper Peninsula, western, and northern Michigan, as per the National Oceanic and Atmospheric Administration’s Great Lakes Aquatic Nonindigenous Species Information System. The most recent observation occurred in 2008, according to bridgemi.com.

Despite the euthanization of 31,000 fish, Eisch emphasized that this number is insufficient to impact the overall Atlantic salmon population for Michigan anglers.

Even if an angler catches an infected fish, it remains safe to consume as long as it is properly cooked since most pathogens or parasites do not survive the temperatures used in cooking, Eisch reassured Bridge Michigan.

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