Why are these Mexican fish doing the wave

In the sulfur-filled ponds in Mexico’s Tabasco state, a tiny silver slip of a fish, sulfur molly, lives. Throw a rock, and you might see a bunch of them dancing: the surface of the water will explode in pale, pulsating waves, spreading across the frightening blue like milk through coffee. Every few seconds, thousands of fish repeat a rapid diving motion to generate the wave, sometimes for up to two minutes.

why? Biologists asked. What purpose can this flash serve?

Mollies are prey for a range of winged predators, including egrets, kingfishers and kiskades. When birds dive to attack, molars flash and spin. Scientists in Germany, unable to visit the fish due to the coronavirus pandemic, have analyzed hours of videos taken over two years of bird attacks, both real and simulated by a researcher, and believe they may have decoded the message sent by the fish.

They seem to target predators that are perched on the beach, hmm Report in Current Biology on Wednesday. Message text: See you. We are watching. Don’t try any funny business.

Not every bird attack causes an eerie flash, said David Berbach, a biologist at the Leibniz Institute for Freshwater Ecology and Inland Fisheries, and author of the new paper. For example, Kingfishers shoot in the water and provoke mollies to flash almost every time. But the kiskadees are subtle — they just dip their beaks. It rarely elicits a response.

This observation gave the researchers a way to test their hypothesis that blinking could lead to a change in the behavior of predators. They set up perches along the sulfur stream as well as cameras to film hunting kiskadees. After a bird hovers over the water, a researcher carrying a slingshot elicited the fish’s waving behavior, mimicking something kiskadees routinely saw when kingfishers were hunting alongside them. Now they can compare undisturbed fishing with turbulent fishing.

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When the fish were rippling and tumbling, the kiskadees sat on the nearby roosts. Over the course of more than 200 hunting sessions, the researchers saw that the birds waited twice as long before starting to pass again compared to how long the water remained undisturbed. When they attacked again, they were less successful in catching a fish than in standing water.

Without the researchers’ intervention, the birds caught a fish more than half the time. With the slingshot running, that was less than a quarter of the time. When the researchers watched the fisherman, they saw that the more the fish flashed, the longer the birds waited, as if they were waiting for them, too.

The response indicates that the blinking behavior not only makes it difficult for predators to focus on a fish, but also that the birds know that their efforts are likely to be lost once the waves start.

This is an interesting observation, because if the fish were just trying to escape from predators, they could dive deeper and stay at the bottom longer. Dr. Bierbach said that although the low-oxygen environment of the sulfur basin means they cannot stay underwater indefinitely, they are perfectly capable of surviving much longer at the bottom.

«They can stay for up to two or three minutes underwater,» he said. “But they don’t. They quickly return to the surface and repeat the dive very synchronously and very rhythmically.”

Simultaneous behaviour, as with flocks of fireflies flashing in unison or flocks of birds moving together in a carefully spaced pattern across the sky, has long fascinated scientists and anyone else lucky enough to see them. But so far, it has proven difficult to determine exactly what benefit the creatures get from them and why they may have evolved.

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Moly sulfur appears to be one of the rare cases in which the benefits of synchronous behavior can be dispensed with.

Dr. Bierbach said the birds learn to «avoid these shoals of fish waving afterwards because the chance of getting a fish is less if waving occurs — and the fish are not eaten, which is a win-win situation.» «This is how a signal can evolve, if both parts, the sender and the receiver, benefit from it.»

There is still a lot to learn in the sulfur ponds in Tabasco.

«Right now, we’re just looking from the top at what’s going on,» Dr. Bierbach said. «And now we want to go underwater, with underwater cameras.»

The researchers hope to discover how the first fish to dive are able to send signals to others, and whether their dive varies with the type of disturbance.

«We have to go under the water to see it,» he said.

Olga Dmitrieva

Любитель алкоголя. Возмутитель спокойствия. Интроверт. Студент. Любитель социальных сетей. Веб-ниндзя. Поклонник Бэкона. Читатель

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