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Tapping on the Aquarium Glass: What Effects on Fish?

Tapping on the Aquarium Glass What Effects on Fish 1

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The Experiment

Does tapping on the aquarium glass pose dangers to fish? At the Schönbrunn Zoo in Austria, two scientists analyzed the noise pollution in aquariums and studied the behavior of visitors who engaged in this activity. The results of the experiment were quite surprising.

Tapping on the Aquarium Glass: The Test

A waterproof microphone connected to a receiver was hidden in a one-cubic-meter aquarium. Whenever a visitor tapped on the aquarium glass, the device would instantly turn on and record the action. The four-week-long experiment conducted by Helmut Kratochvil and Harald Schwammer focused on the behavior of aquarium visitors who had the habit of tapping on the glass. The tests were conducted in batches of 100 visitors from Monday noon to Friday noon and from Friday noon to Monday noon. Three different signs were then placed, stating “Tapping on the aquarium glass kills the fish,” “Only the foolish tap on the glass,” and “Please refrain from tapping on the glass.”

Tapping on the Aquarium Glass What Effects on Fish

Results of the Experiment

The recorders registered a higher number of taps on the aquarium glass during the week, which was likely due to the high influx of school visitors. Out of 100 visitors, approximately 2 visitors tapped on the glass. On days with high attendance, the zoo can receive up to 15,000 visitors, resulting in approximately 300 taps on the glass. In the most severe cases, a single person would tap three to four times on the aquarium walls. The recorders even counted 72 consecutive taps, which represents a severe trauma for the fish. For humans, repeated shocks like these could lead to hearing impairment.

However, for fish, the effects are even worse: the acoustic pressure is greater in water than in air, and the resulting waves from the taps have a very powerful effect. Consequently, it is assumed that in many cases, the death of fish in aquariums is directly linked to this unfortunate phenomenon.

Warning Signs

In general, visitors tap on the walls of aquariums or terrariums to startle an inactive fish, make it move, or get its attention.

So, the question that arises is: how can this behavior be minimized among visitors? To find an answer, the two scientists successively displayed one of the three signs on the front wall of the aquarium for two weeks. The conventional sign stating “Please refrain from tapping on the glass” resulted in a 72% reduction in taps on the aquarium. The sign “Tapping on the aquarium glass kills the fish” yielded better results, as it led to an 82% decrease in noise disturbances. Topping the list was the boldest sign, which read “Only the foolish tap on the glass.” Consequently, approximately 90% of the aquarium visitors refrained from attracting the attention of the two freshwater rays in the aquarium.


The results presented in this article should encourage public aquariums to implement similar warning signs. On one hand, the findings of this experiment provide a good understanding of the influence visitors can have. On the other hand, to fully protect the fish from such noise disturbances, new aquarium designs should prevent visitors from accessing the walls and tapping on the aquarium glass.

mahatma gandhi portrait

- Mahatma Gandhi

“The greatness of a nation and its moral progress can be judged by the way its animals are treated.”

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