Environmental scientists at IGB, The Leibniz-Institute of Freshwater Ecology and Inland Fisheries, the research institute in Germany, found that artificial lighting at night affects melatonin reproduction in fishes.

It is widely acknowledged that melatonin plays a critical role in regulating circadian rhythm of human bodies. And a research team now proved that lighting also suppresses production of melatonin in fishes. The team of IGB researchers investigated melatonin production in European perch and showed that light pollution, like nighttime urban sky glow, is bright enough to suppress melatonin production and affect fish’s circadian rhythm.

(Image: IGB; Michael Feierabend)

The research exposed fish to daylight during the day and put them under different light at night. The control group spent the night in complete darkness, whereas the other three groups were exposed to light intensities at 0.01, 0.1 and 1 lux. After ten days, the scientists measured melatonin levels at three-hour intervals over a period of 24 hours. The result showed that even the lowest light intensity of 0.01 lux was enough to suppress melatonin production; higher light intensities led to an increasingly strong gradual reduction of melatonin.

For comparison, illumination intensities to which organisms are exposed at night: on a crystal clear night, illumination intensity is less than 0.001 lux. On a full moon night, it measures a maximum of 0.3 lux. Sky glow over a city can reach illumination intensities of up to 1 lux and more, and street can lighting anything up to 150 lux.

Researchers noted that fishes spend much of their lives asleep and need sleep to regenerate. IGB’s Professor Werner Kloas, lead investigator of the study, explained the effects of disturbed melatonin levels: “Our previous research methods do not enable us to assess whether urban fish experience a lack of sleep due to light pollution. However, we assume this is the case because melatonin is an important factor influencing sleep in vertebrates, including fish. One thing for sure is that other body functions such as immune defence, growth and reproduction can be disturbed by altered melatonin production.“