Approximately 100 fish died in Launt Pond in Walton over the weekend of June 15 because of a disease, according to the state Department of Environmental Conservation.
While the disease isn't known to be a health risk to humans — the culprit bacterium doesn't grow well at the temperature of the human body — it is often deadly to fish. DEC staff members who work onsite first noticed the fish kill, a DEC spokesperson told The Daily Star in an email exchange.
DEC partners at Cornell University took samples from Launt Pond and determined the cause of the fish kill was columnaris. Columnaris is a fish disease caused by a type of bacterium called Flavobacterium columnare that is often prevalent in fresh water and cultured fish reared in ponds or raceways. A follow up laboratory analysis of the water showed no other issues, the DEC spokesperson said.
The disease-causing bacterium lives in water and mud and is found on the bodies of fish and in the gill area, according to a fact sheet by the Ontario Ministry of Natural Resources. Bacteria can enter the fish through the gills or broken skin. Fish across the world can experience columnaris, and bullheads and catfish are particularly susceptible.
Outbreaks occur when fish are undergoing some type of stress, including low oxygen level in the water, excessive handling, crowding or unfavorable temperatures, according to the OMNR fact sheet. Columnaris is more easily transmitted in higher water temperatures, according to a 2009 study in Proceedings of the Royal Society B: Biological Sciences.
Brown bullhead was the primary affected species, the DEC spokesperson said. These fish had recently completed their spawning process, which is a stressful ritual for them. The spokesperson said this stress likely facilitated the spread of the latent pathogen.
The species impacted are native to the pond. The state stocks brook trout, which were not affected by the columnaris outbreak, the DEC spokesperson said.
Signs of columnaris in fish are sores on the gills and body that are white to brown, grayish-white or orange-yellow, according to the OMNR fact sheet. Infected fish may also be seen with sores or ulcers on the fins, head and body that eventually increase in size and may expose the underlying muscle. In very severe cases, fish can display ulcers on the mouth and jaw. Some infected fish show no signs but carry the bacteria in their kidneys.
Columnaris outbreaks in the wild are nearly impossible to prevent or treat, according to the OMNR fact sheet. Outbreak risk in cultured fish in the salmon family can be reduced by keeping the water temperature low. Handling in warm weather should be minimized, crowding avoided and water should be reused with caution. If an outbreak is suspected, consult a veterinarian.
Shweta Karikehalli, staff writer, can be reached at firstname.lastname@example.org or 607-441-7221. Follow her @DS_ShwetaK on Twitter.