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These fish gather together and create huge waves to scare off predatory birds

Just as in soccer matches, attendees create 'human waves' to celebrate a goal, the Teapa mollies do something similar to scare away their predators. According to a study published in the journal 'Current Biology', these fish work together in groups of up to hundreds of thousands of specimens to create surface waves and scare away possible attackers.

“The surprise came after we realized how many fish can act in such repeated waves”, explains Jens Krause , from the Leibniz Institute for Freshwater Ecology and Inland Fisheries in Berlin and the Cluster of Excellence Science of Intelligence. “There are up to 4,000 fish per square meter and sometimes hundreds of thousands of fish participate in a single wave.

Fish can repeat these waves for up to two minutes, with one wave every three to four seconds or so. '

The Teapa molly (Poecilia sulphuraria) is an endemic fish from Mexico, specifically from the Azufre Baths near Teapa, Tabasco. Sulfur Baths are sulfidic springs that contain high toxic concentrations of hydrogen sulfide, although this species has evolved to tolerate these critical conditions. “At first we didn't really understand what the fish were doing,” says David Bierbach , co-author together with Carolina Doran and Juliane Lukas, also at the Leibniz Institute of Freshwater Ecology and Continental Fisheries-. Once we realized that they were waves, we wondered what their function could be.

The first thing that reminded them was precisely the waves that fans create by raising their arms at football matches. However, the presence of many fish-eating birds around the river made them think that this behavior was likely some kind of defense mechanism, not exactly celebratory. That is why they investigated whether this phenomenon could scare off predators. And so it was: they found rhythmic and repetitive patterns that frightened the hunters, who took twice as long to attack again . In addition, the probability of capture also decreased with the number of waves, apart from the fact that the birds also changed their position in response to this movement, which suggests that they would have decided to change their targets.

“Until now, scientists have mainly explained how collective patterns arise from the interactions of individuals, but it was not clear why animals produce these patterns in the first place,” says Krause. Our study shows that some patterns of collective behavior can be very effective in providing protection against predators. ”

The researchers note that although it is clear that these waves reduce the chances of a successful hunt, what is still unanswered is why these birds carry out these evasive movements: do they mistake the waves for other birds? Do these waves indicate to them that they have been detected and, therefore, that they are less likely to hunt successfully? The group will try to answer this question in further studies.

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