Does light pollution in urban areas affect sleeping fish? Researchers looked at the effect of different light levels on the production of melatonin, a hormone that regulates the diurnal patterns of animals, in European perch (Perca fluviatilis). Four groups of fish were set up; a control group that spent nights in complete darkness, and three groups that were exposed to different levels of light at night (0.01, 0.1 and 1 lux). All fish groups were exposed to full light during the day (2900 lux). After ten days of these conditions, the researchers tested the tank water for all four groups every three hours for 24 hours.
What researchers found is that even the lowest intensity light levels was enough to suppress melatonin. Low light intensities of 0.01 lux and 0.1 lux, which mimic the skyglow, or urban/suburban night light pollution, are enough to disrupt the physiological functions of European perch.
The findings of the researchers aligns with other studies that have found that the persistent presence of night light pollution impairs the ability to produce melatonin.
Kupprat, F., Hölker, F., & Kloas, W. (2020). Can skyglow reduce nocturnal melatonin concentrations in Eurasian perch? Environmental Pollution, 262, 114324. https://doi.org/10.1016/j.envpol.2020.114324