Do fish ever get tired

Do City Fish Sleep Worse? Light pollution suppresses melatonin formation in perch

Research results, scientific publications

Melatonin clocks the internal clock, thanks to a high melatonin level people get tired in the evening. Melatonin is also important for the biorhythm of animals. Artificial light at night - light pollution - can suppress the formation of melatonin in fish even at very low light intensities, researchers at the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) discovered.

Melatonin shapes the day-night rhythm in humans and vertebrates. Organs, tissues and cells set their internal clock depending on the concentration of this hormone. As a result, melatonin also controls processes such as reproduction and growth. Vertebrates and humans perceive differences in the brightness of their surroundings via light receptors, for example on the retina in the eye. When a lot of light hits the receptors, the formation of melatonin is suppressed, whereas in the dark, a lot of melatonin is formed. Artificial light at night can disrupt the melatonin balance.

The IGB team investigated the melatonin production of European perch. During the day there was daylight for all animals, at night the lighting varied depending on the group: The control group spent the night in complete darkness, the other three groups were exposed to light intensities of 0.01, 0.1 and 1 lux. After 10 days, the researchers determined the melatonin concentrations at intervals of three hours over 24 hours. The result: Even the lowest lighting intensity of 0.01 lux reduced the formation of melatonin; at the higher lighting intensities, melatonin was gradually reduced more and more.

In comparison, the illuminance levels experienced by living beings at night: On a clear, starry night, the illuminance is less than 0.001 lux. On a full moon night, it reaches a maximum of 0.3 lux. The light dome of a city can achieve illuminance levels of up to 1 lux and more, street lighting can even achieve up to 150 lux.

Even the night light in cities suppresses the formation of melatonin:

“The astonishing thing is that the intensities of a city's light dome are sufficient to suppress melatonin formation in fish,” says first author Franziska Kupprat from IGB. Large areas around the world are affected by this type of light pollution. The light from artificial lighting shines in the sky and is reflected on clouds and particles, creating a large bell of light that goes beyond the actual illumination radius of the light source.

The lighting intensity had no influence on the rhythm of melatonin formation. Melatonin formation increased in all animals in the course of the afternoon and reached its maximum value at night. "Earlier studies have shown that higher intensities of nocturnal lighting such as 10 and 100 lux also influence the melatonin rhythm of the perch, as the melatonin formed at night was so greatly reduced that no difference to the low daily values ​​could be measured", explains Dr. Franz Hölker from the IGB.

Pisces oversleep much of their lives, just because they don't have eyelids, you can't see it. As with other living beings, sleep helps them to regenerate. Study leader Professor Werner Kloas from IGB explains the effects of a disturbed melatonin balance: “With our previous scientific methods, we cannot assess whether city fish suffer from a sleep deficit due to light pollution. However, we suspect it is because melatonin is an important factor influencing the sleep of vertebrates, including fish. What is certain is that other body functions such as the immune system, growth and reproduction can be disrupted by altered melatonin formation. "


Scientific contact:
Franziska Kupprat
Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB)
PhD student
Department of Ecophysiology and Aquaculture
Email: [email protected]

PD Dr. Franz Hölker
Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB)
Head of the Light Pollution and Ecophysiology Research Group
Department of Ecohydrology
Email: [email protected]
Original publication:
Franziska Kupprat, Franz Hölker, Werner Kloas (2020). Can skyglow reduce nocturnal melatonin concentrations in Eurasian perch? Environmental Pollution, Volume 262 https://doi.org/10.1016/j.envpol.2020.114324