Do fish need a dark environment at night?

Question

Is it bad if I accidentally leave the lights lit on a fish tank overnight? Or do the fish not care whether it is light or dark?

score 17 · Accepted Answer · edited Aug 23 '14 at 23:38

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Fish do care if it´s day or night: they have a cicardian rhythm and many physiological events are related to the day / night time. Light could interfere with that. Source: this book, chapter 6.

Even blind fish can have a cicardian rhythm

Leaving the aquarium light accidentally lit for one night won´t instantly kill them but will cause some stress.

edited Aug 23 '14 at 23:38

CGCampbell

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answered Oct 09 '13 at 15:40

woliveirajr

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Why not just connect your lights to a timer that will shut it off automatically at a given time each day?! – martin Oct 09 '13 at 18:56
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Also leaving the lights on for long periods can increase algae growth - which, as well as being unsightly, can decrease oxygen levels in the tank. – starsplusplus Jul 18 '14 at 12:41
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As an addendum, the night is also required for some plants. Compare for example this question. – Voitcus Jun 02 '15 at 10:46

score -1 · Answer 2 · answered Jan 08 '21 at 03:05

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I would set a light with a timer, fish are less active when the tank is dark and can get stressed, which means they are more vulnerable to illness.

answered Jan 08 '21 at 03:05

Flyhighwhiskers

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Do fish need a dark environment at night?

2 Answers2