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How long can goldfish stay in the dark?

How long can goldfish stay in the dark?

Goldfish are a popular pet fish that have been kept as pets for hundreds of years. One aspect of goldfish care that many goldfish owners wonder about is how long goldfish can survive without light. Goldfish do not actually require light to survive, but keeping them in prolonged periods of darkness can impact their health and wellbeing. In this article, we will explore how long goldfish can stay in the dark, the impacts of keeping goldfish in the dark, and best practices for lighting for your goldfish tank.

How Long Can Goldfish Physically Survive Without Light?

Goldfish can physically survive without light for quite a long time. Here is an overview of how long goldfish can survive without light:

Timeframe Impact on Goldfish
2-4 Days No major impact, goldfish can function normally
1-2 Weeks May become more lethargic, loss of coloration
2+ Weeks Increased risk of disease, may stop eating
1-2 Months High risk of disease, organ damage, and death

As you can see, goldfish can physically survive without light for quite a while. Their bodies are adapted to function in low light conditions. However, after about two weeks, the goldfish will begin to show signs of stress, illness, and deterioration. Prolonged periods of 2 months or more in complete darkness could eventually lead to death.

So in summary, goldfish can survive purely physically for 2-4 months without light, but will become very unhealthy in this timeframe without light exposure.

Impacts of Keeping Goldfish in the Dark

While goldfish can physically survive in the dark, lack of light exposure can cause a number of detrimental impacts to their health and wellbeing:

– **Disrupted Circadian Rhythms** – Goldfish, like many animals, have circadian rhythms that are influenced by exposure to light and dark. Keeping them in 24/7 darkness disrupts these rhythms which can impact appetite, activity levels, and physiology.

– **Color Loss** – Many goldfish varieties have bright pigmentation. Lack of light causes loss of coloration and faded, pale appearances.

– **Increased Susceptibility to Disease** – Over time, lack of light appears to compromise goldfish immune systems and make them more prone to bacterial and parasitic infections.

– **Decreased Activity Levels** – Goldfish tend to become more lethargic and less active without regular light exposure.

– **Failure to Thrive** – Goldfish kept in constant darkness may exhibit poor appetite and growth over time and can eventually succumb to malnutrition and organ damage.

– **Stress** – Although goldfish do not require lighting, a complete lack of light is an unnatural and stressful environment for them long term. Chronic stress negatively impacts health.

So while goldfish can survive in the dark, there are many downsides to keeping them without lighting that should be avoided. Some intermittent darkness is fine, but goldfish need regular day/night light cycles for their health.

Do Goldfish Need Lighting?

Goldfish do not technically need lighting the way some animals like corals and plants do. However, regular light/dark cycles are still very important for their biological rhythms and overall health. Here are some general lighting guidelines for goldfish:

– Goldfish should have some daytime ambient lighting for 10-12 hours per day. Natural daylight near a window works well for this.

– If ambient light is low, the tank will need supplemental artificial lighting. Standard fluorescent or LED aquarium lighting can be used.

– Lighting intensity does not need to be extremely bright – a moderate level is fine for goldfish care.

– Lights should be off for around 10-12 hours per day to allow for nighttime/darkness. Automatic timers help maintain the lighting schedule.

– Complete darkness should be avoided. If the tank is in a naturally dark room, a low wattage night light can prevent it from being pitch black at night.

While goldfish do not need light, following these general lighting guidelines helps promote healthy circadian rhythms and prevent problems caused by too much darkness.

Ideal Lighting Schedules for Goldfish Tanks

The ideal lighting schedule for a goldfish tank balances adequate daytime light exposure with a long enough nighttime dark period. Here are some sample lighting schedules that work well:

Time Period Tank Lighting
7 AM – 7 PM (12 hours) Daytime lights on
7 PM – 7 AM (12 hours) Nighttime lights off
Time Period Tank Lighting
8 AM – 8 PM (12 hours) Daytime lights on
8 PM – 8 AM (12 hours) Nighttime lights off
Time Period Tank Lighting
10 AM – 10 PM (12 hours) Daytime lights on
10 PM – 10 AM (12 hours) Nighttime lights off

The exact schedule can be adjusted based on your household schedule. The key is maintaining around 12 hours of light and 12 hours of darkness. Automatic light timers help stick to a consistent schedule.

Signs Your Goldfish Are Not Getting Enough Light

Here are some signs that your goldfish may not be getting adequate lighting:

– Loss of bright coloration
– Staying inactive and hiding during times they are normally active
– Not responding to feeding times or loss of appetite
– Appearing generally lethargic and restless
– Increased susceptibility to disease
– Rapid gill movement or gasping at surface
– Clamped fins or frayed fins
– Goldfish stuck to filter intakes or other surfaces

If you notice any combination of these signs, lack of sufficient lighting could be the cause. Try increasing daytime lighting to 10-12 hours per day and observe if your goldfish perk up.

Using Natural Sunlight in Your Goldfish Tank

Natural sunlight can provide an excellent daytime light source for goldfish tanks. Here are some tips for using sunlight:

– Place tank near, but not directly touching, a sunny window. South or West facing windows work best.
– Make sure no direct sun beams shine directly onto the tank, as this can overheat the water. Sheer curtains can help diffuse direct sunlight.
– Check that ambient room light is low enough at night – blinds or curtains may be needed at night.
– Avoid too much direct sunlight, as this promotes excessive algae growth.
– Natural daylight avoids the need for supplemental tank lighting during the day.

When used properly, natural sunlight provides the lighting intensity and variations that goldfish thrive on. Just be careful not to allow too much direct sunlight, and make sure the tank is not too brightly lit at night. With a little trial and error, sunlight can work very well.

Using Artificial Lighting for Your Goldfish Tank

If natural sunlight is insufficient, artificial aquarium lighting is needed to properly light your goldfish tank. Here are some guidelines on choosing lighting:

– **Florescent bulbs** – Linear florescent bulb fixtures are an economical choice. Go with daylight or full spectrum bulbs.
– **LED fixtures** – LED lights last longer and are more energy efficient. Full spectrum or 6500K lighting works well.
– **Low wattage** – Goldfish do not need intense light. Standard fluorescent or LED strips around 6500K color temperature are perfect.
– **Avoid night lights** – Blue or moonlight LEDs disrupt proper day/night cycles. Use timers for daytime lighting only.
– **Automate lighting** – Use automatic timers to maintain a consistent 12 hours on, 12 hours off schedule.

With artificial lighting, it’s important to get the photoperiod right. The wrong lighting duration or improper spectrum can negatively impact goldfish health. Carefully follow lighting recommendations when using artificial lights.

Lighting for Outdoor Goldfish Ponds

For outdoor goldfish ponds, sunlight provides all the lighting needed during the day. Here are some tips for pond lighting:

– Make sure pond gets at least 6 hours of direct sunlight daily. More is preferable.
– If pond is shaded, consider trimming back nearby trees and shrubs.
– Artificial lighting is not necessary during the day, but can extend viewing time in evenings.
– Optional pond lights should be used only for short periods in evening when fish are normally inactive.
– Pond depths over 18 inches will remain naturally dark at night, even with pond lights on. This allows for normal day-night cycles that goldfish need.

Outdoor goldfish get abundant natural daylight. Carefully positionedaccent lighting can provide some evening pond viewing without disrupting goldfish routines. But additional daytime lighting is rarely needed in ponds.

Tips for Providing Proper Lighting for Goldfish

Here are some tips to ensure proper lighting for your goldfish tank or pond:

– Stick to a consistent 12 hours on, 12 hours off lighting schedule every 24 hours. Automate lights with a timer.

– For indoor tanks, make sure daytime light intensity is moderate. Natural sunlight or standard aquarium light fixtures work well.

– Avoid complete darkness at night. Indoor tanks benefit from a low wattage night light.

– Position the tank or outdoor pond so it receives ample ambient natural light during the daytime from a nearby window or sky exposure.

– Avoid too much direct sunlight on the tank or pond, as this can promote excessive algae growth.

– If using artificial lights, choose fixtures with daylight or full spectrum bulbs in the 5000K-7000K color temperature range.

– Monitor goldfish for signs of insufficient lighting like loss of color or appetite. Increase duration or intensity if needed.

Providing proper lighting really comes down to maintaining a consistent, moderate-level day/night cycle without prolonged periods of darkness. Doing so will keep goldfish active and healthy.


In conclusion, while goldfish do not technically require lighting, exposure to regular periods of daylight and darkness is crucial for their health and wellbeing. Goldfish can physically survive in complete darkness for 2-4 months, but will gradually deteriorate without any light. Prolonged darkness leads to issues like disrupted bio rhythms, color loss, disease susceptibility, lethargy, and stress.

Ideally, goldfish should get around 12 hours of moderate ambient daylight each day, and about 12 hours of darkness each night. Natural sunlight near a window works great for indoor tanks, supplemented by artificial lighting as needed. Outdoors, sunlight provides more than enough daytime light. Care should be taken to prevent too much direct sunlight, which can encourage excess algae. Proper lighting promotes active, healthy goldfish, so be sure to provide lights on a consistent daily schedule. With the right balance of light and dark periods, goldfish can thrive for many years.