title: Spotlight on fish: light pollution affects circadian rhythms of European perch but does not cause stress.
abstract: Flora and fauna evolved under natural day and night cycles. However, natural light is now enhanced by artificial light at night, particularly in urban areas. This alteration of natural light environments during the night is hypothesised to alter biological rhythms in fish, by effecting night-time production of the hormone melatonin. Artificial light at night is also expected to increase the stress level of fish, resulting in higher cortisol production. In laboratory experiments, European perch (Perca fluviatilis) were exposed to four different light intensities during the night, 0 lx (control), 1 lx (potential light level in urban waters), 10 lx (typical street lighting at night) and 100 lx. Melatonin and cortisol concentrations were measured from water samples every 3h during a 24 hour period. This study revealed that the nocturnal increase in melatonin production was inhibited even at the lowest light level of 1 lx. However, cortisol levels did not differ between control and treatment illumination levels. We conclude that artificial light at night at very low intensities may disturb biological rhythms in fish since nocturnal light levels around 1 lx are already found in urban waters. However, enhanced stress induction could not be demonstrated.
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany. Electronic address: bruening@igb-berlin.de.
authors.forename: Anika
authors.initials: A
authors.lastname: Brüning
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany. Electronic address: hoelker@igb-berlin.de.
authors.forename: Franz
authors.initials: F
authors.lastname: Hölker
authors.affiliation: Leibniz Institute for Plasma Science and Technology, Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany. Electronic address: steffen.franke@inp-greifswald.de.
authors.forename: Steffen
authors.initials: S
authors.lastname: Franke
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany. Electronic address: preuer@igb-berlin.de.
authors.forename: Torsten
authors.initials: T
authors.lastname: Preuer
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany. Electronic address: werner.kloas@igb-berlin.de.
authors.forename: Werner
authors.initials: W
authors.lastname: Kloas
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D005399:Fishes; D006854:Hydrocortisone / Q000378:metabolism; D008027:Light; D008550:Melatonin / Q000378:metabolism; D010471:Perches / Q000502:physiology*; D010775:Photic Stimulation
chemical_list: D008550:Melatonin; D006854:Hydrocortisone
keywords: Fish; Light intensity; Light pollution; Non-invasive hormone measurement; Perca fluviatilis