Artificial light at night makes guppies more courageous during the day, according to a new behavioral study. Researchers exposed fish to artificial light at night, which not only made them more active during the night, but also made them emerge quicker from hiding places during the day. It is expected that these behavioral characteristics will increase their exposure to predators.
What is Light Pollution?
Excessive and inappropriate artificial light, known as light pollution, is responsible for the disappearance of the Milky Way from our night skies. Professional astronomers must use observation sites far away from air pollution for a clear view of the skies. Research has also linked the brightening night sky to measurable negative impacts on human health and immune function, as well as a host of adverse behavioral changes in insect and animal populations (Dark Skies Awareness).
Current study design
The researchers used guppies, a tropical freshwater fish and a model organisms of animal behavioral science. The scientists studied three groups of animals. Each group was exposed to the same bright light condition during the day, but to different illuminations during the night. The first group (control) experienced complete darkness at night; the second group was kept at a low light level at night, comparable to nocturnal illuminance under a street lamp; and the third group experienced bright light at night.
After ten weeks of exposure, the scientists conducted behavioral tests to study the consequences of light exposure at night on daytime behaviors.
Fish left their hiding places faster during the day and swam more often in the riskier, open areas of the aquarium when exposed to strong, but also weak, artificial light at night. It is difficult to predict, but it’s possible that light pollution could increase risk of predation by birds or other fish.
“We suspect that the nocturnal light causes a stress response in the fish, and fish generally increase their risk taking when experiencing stress,” explains Ralf Kurvers.