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Dead fish do tell tales: Using the necrobiome to measure impact of wastewater on aquatic life

Thursday, July 27, 2017

Waterloo Biologists Paul Craig and Andrew Doxey find fish struggle to live in the Grand River downstream from Kitchener, Ontario’s wastewater treatment plant.

Rainbow darter fish in a respirometer used to measure metabolic activity.And it’s no wonder. The researchers found potentially harmful bacteria thriving as part of what’s known as the necrobiome, bacteria associated with dead and decaying organisms.

"We can see that fish from effluent-contaminated waters are enriched in pathogenic bacteria associated with human infections including species that cause food poisoning such as Clostridium perfringens," says Doxey, a professor of biology with a cross appointment to computer science. He is also a member of Waterloo’s Centre for Bioengineering and Biotechnology.

Their study, presented by Craig at the annual meeting for the Society for Experimental Biology in Gothenburg, Sweden, is the first of its kind to analyze this important, but overlooked microbial community that amplifies what fish and other wildlife are being exposed to beyond what’s in the water and sediment.

"Decaying fish can act as a sink for the spread of harmful bacteria to scavenging fish and birds. Fish caught in areas downstream of effluent outlets may also pose a health risk to anglers," says Craig, a professor of biology and a member of Waterloo’s Water Institute.

Further study of rainbow darters, a common fish in the Grand River, found their exposure to the wastewater increased their metabolic rates, indicating that the fish required more energy to survive, leaving less energy to find food, attract mates or escape predators.

"This increase in metabolic rate is likely the result of a costly immune response to overcome infection from these pathological bacteria," says Craig.

When the fish were returned to clean water, their rates returned to normal after a week, raising hopes that current upgrades to the wastewater treatment facility will result in a rapid recovery of the local river ecosystem.

Craig and his team acknowledge Metagenom Bio Inc. for their work in DNA sequencing and contributing some analysis on this project.


Science in the MediaThis story was featured in:

  • Sleeping with the Fishes — Decay in Wastewater Damages Aquatic Life. July 6, 2017. Invisiverse.
  • One fin in the grave: Necrobiome poses a health threat to fish. July 5, 2017. Eurekalert and Phys.Org.
  • Fish exposed to sewage in water can spread bacteria. July 5, 2017.  Earth.com
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