Czech scientists use fish scales to monitor water quality

Bream in the Římov reservoir, photo: Jiří Peterka / Czech Academy of Sciences

Czech researchers have become the first in the world to use fish scale samples to map the changing quality of water. A new study, published in the prestigious international magazine Science of the Total Environment, shows that fish scales are a reliable source of information about human impact on the water ecosystem.

Just like tree rings store information about the history of the Earth’s climate, so can fish scales tell us about the history of the aquatic ecosystem.

Using samples of scales from the Římov reservoir in South Bohemia, a team of researchers from the Czech Academy of Sciences have analysed the quality of its water from 1979, when it was first filled, to the present.

Mojmír Vašek,  photo: archive of Czech Academy of Sciences

Mojmír Vašek, one of the members of the team, explains they have focused on two substances, carbon and nitrogen isotopes:

“These two isotopes can provide information about the environment the fish live in. Analysing its scales, we can see, for instance, how green the water is. That tells us about the amount of planktonic algae.”

The scientists have analysed some 1,200 fish scale samples from two species, the common roach and the common bream, collected over the 40-year history of the reservoir, says mr. Vašek:

“In our study we cut off the edge of the scale representing the last year of the fishes’ life and we analysed that. But what is interesting about our study is the fact that we had samples collected in the reservoir over the past 40 years.”

Římov reservoir,  photo: Jvk,  Wikimedia Commons,  CC BY 3.0

The researchers have subsequently compared their findings with data from the long-term monitoring and the results have matched, proving that the method is reliable.

The Římov reservoir has served as a source of drinking water for the city of České Budějovice, but throughout the 1980s, the quality of its water wasn’t very high.

It was mainly affected by farming and the lack of a water treatment plant. The water contained fertilizers washed off from the nearby fields and was full of algae and cyanobacteria. In the 1990s, the quality of water improved. However, over the past decade it has been stagnating again.

In the future, researchers from the Czech Academy of Sciences would like to use the same method to analyse water from other lakes and reservoirs in the country, which haven’t been monitored as closely as Římov, explains Mr. Vašek:

Photo: Petr Znachor / Czech Academy of Sciences

“Many lakes and reservoirs in the country may have not been monitored as closely, but there are fish scales available.

“So analysing them retrospectively, we can find out how their water quality has been changing.”

The new method can also be used to monitor the content of other substances in the fish scales, such as mercury, and can be also employed to look deeper into the past, using fish scales from archaeological findings, for instance.

Authors: Ruth Fraňková , Martin Srb
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