Water Institute researcher measures the effects of waste water on the metabolism of fish

Friday, July 14, 2017

Sewage-contaminated water is even more harmful for aquatic life than previously thought, according to researchers in the University of Waterloo’s Department of Biology. Paul Craig, Water Institute member and assistant professor in the Department of Biology, and his research team are the first to examine the effects of the bacterial necrobiome on fish exposed to wastewater.

"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,” said Craig.

paul craig

This study analyzes how the unique community of bacteria associated with dead and decaying organisms, known as the necrobiome, is affecting the metabolic performance of rainbow darters. Craig and his team examined this by measuring the rate of breathing in fish exposed to contaminated water in the Grand River Watershed using custom-made respirometry chambers.

"We saw an increase in metabolic rate in fish exposed to wastewater effluent. This indicated that these fish were under environmental conditions that required more energy to survive in a resting state, leaving less energy to find food, attract mates or escape predators,” said Craig.

rainbow darter

In addition to harmful pollutants such as pharmaceuticals, Craig's co-author Andrew Doxey, assistant professor in the Waterloo’s Department of Biology, described how the effluent contaminated wastewater is also a source of pathogenic bacteria:

"We can clearly see that fish from effluent-contaminated waters are particularly enriched in pathogenic bacteria most associated with human infections, including bacteria that cause food poisoning such as Clostridium perfringens.”

When wastewater exposed fish were returned to clean water, the metabolic rate returned to normal after a week, prompting Craig and his team to investigate the role of the necrobiome:

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

Wastewater from the Grand River site was found to have different kinds of human pathogenic bacteria in it. Clostridium perfrigens, Aeromonas veronii, and Eubacterium tarantellus were all present in the wastewater. They all are known to cause sickness, and the researchers found them in the necrobiome of dead fish in the study.

“The necrobiome itself is associated with the decaying fish, however, the type of bacteria that become enriched as the fish decays is attributed to whatever the fish was exposed to while it was alive — such as wastewater or the natural, inherent microbiome that is found in the gut. While wastewater is very low in pathogenic bacteria, a way of identifying and enhancing this is through the necrobiome of organisms exposed to wastewater,” said Craig.

Craig and his team will have a unique opportunity to compare fish from the same sites after the completion of planned upgrades to Grand River’s wastewater treatment facilities. They are hopeful that the improvements will help reduce levels of pollutants and pathogenic bacteria coming from these facilities into waterways and minimize their impact on fish.

Craig and his team wanted to acknowledge Metagenom Bio for their work in doing the sequencing and contributing some analysis on this project.

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