Frequent blinking affects the behavior of other fish in school.
Lampfishes have the ability to create situation-specific flash patterns similar to the visual Morse code. Researchers at Ruhr-Universität Bochum have shown in laboratory and field experiments that animals use these light signals to coordinate their behavior at school when vision is limited. The light intensity and the frequency of blinking influenced the behavior of the animals. The team headed by Peter Jägers and Professor Stefan Herlitze from the Department of General Zoology and Neuroscience shared their findings in the journal. Scientific Reports, Which was published online on March 19, 2021. “Our data shows that lampfish are attracted to the light signals emitted by other school members,” notes Jägers.
Milky Way in the water
Lampfish Anomalops katoptron has a luminous organ under their eyes that is full of illuminating bacteria that can close so that they appear to flash. During the day, animals hide in caves, rocky crevices, or in deep, dark waters. “On moonless nights, up to a thousand people at a school migrate to surface waters rich in plankton,” says Peter Jaggers, who observed fish in the wild during an expedition in the Indian and Pacific Oceans. “It’s a surreal experience to see schools – like the Milky Way in the water.”
To understand the function of the blinking patterns, the researchers first studied Anomalops katoptron in the laboratory in a large water tank containing fish dolls that can be controlled digitally to mimic the animals’ light signals. They also used infrared cameras to record individual animal movements in response to flashing artificial lights. During the experiments, there was only one animal in the tank at a time, with many individuals testing one by one.
Lamp dolls attract fish
When the researchers placed a single flashing doll in the middle of the tank, the fish moved closer to it as the light flashed faster. In another experiment, 13 lights were placed around the tank and lit one by one at varying intervals of time. “We noticed a large impulse among the lampfishes to direct toward the light,” says Peter Jägers.
Based on laboratory experiments, the researchers concluded that faster flashing is a signal for Anomalops katoptron to stay close to their schoolmates, as the group offers, for example, protection from predators. This theory was confirmed in field trials. On a diving expedition, researchers showed that the animals responded to stress by blinking more quickly.
Waiting for school at night at sea
The researchers plunged into the darkness at night, and waited until a group of lampfishes approached. The animals avoided the brighter moonlight by fleeing immediately. The Bochum team fired the escape response with a faint red light and simultaneously recorded the animals and their flashing patterns with special cameras. This is how they demonstrated that stress is associated with increased blinking frequency. “We assume that increased frequency of blinking is a signal to closely follow other group members under pressure,” concludes Peter Jaggers. “In our study, we showed for the first time that there is a direct link between signals that are visually communicated under limited lighting conditions, such as those prevalent at night or in the deep sea, and the school composition of fish. We hope this will be useful in future studies, for example, Deep sea largely undiscovered. ”