Do fish need sunlight?

Do Fish Need Sunlight? All Questions Answered:

Keeping a fish at home is quite different from a wild fish living in a freshwater or saltwater environment. For the wild fish sun is the basic source of light and it’s inevitable for them. Here the question arises that do fish need sunlight?

The simple one word is No, they do not need sunlight. Despite benefits, there are more drawbacks to a constant supply of sunlight to the aquarium. Thus, it is beneficial not to put an aquarium near a window or a sunlight source.

An artificial light source is more than enough for fish to survive and go about their daily routine.

Let’s discuss the perks and downsides of sunlight for a fish tank in detail.

Why Light Is Necessary for An Ecosystem?

As we are all familiar with the components of the ecosystem, plants, living organisms, microbes, animals, air, water, and a lot of other stuff. Our matter of concern here is microbes, plants, and of course fishes.

For plants, sunlight is the main source of photosynthesis resulting in their growth. This photosynthesis is ultimately an abundant source of oxygen for living organisms to survive. Thus, without this essential photosynthesis, our ecosystem can’t survive.

In the case of a fish tank, photosynthesis does not only result in the growth of plants but can also cause algal bloom. Yes, an abundant algal bloom that can ultimately destroy the aquarium ecosystem can result from a constant supply of sunlight.

Effects of sunlight on aquarium plants:

The only component of an aquarium that needs constant sunlight plants. Plants can only utilize this light from the sun for only 12-14 hours a day. As pants sleep at night and thus there is no photosynthesis.

Production of oxygen:

This light used by plants results in the production of Oxygen necessary for fishes to breathe.

Removal of waste Products:

Waste products such as nitrates and nitrites are used up by plants and thus, they will be removed from the aquarium. Without this sunlight, plants won’t be able to survive and thus there will be a buildup of waste products.

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Algal bloom:

Unlike plants, the alga can use light for more time, thus are quicker to grow. Using the nutrients available in excess algae can overgrow the aquarium.

Thus, an abundant supply of sunlight can result in the overproduction of algae leading to the destruction of the aquarium ecosystem.

Effects of sunlight on aquarium fish:

As it has already been made clear that fish do not necessarily need sunlight, thus there is no significant effect of sunlight on fish. If there is no other source of light for the aquarium sunlight is the only source for fish to view the food and other objects.

Moreover, the timing of sunlight is in direct accordance with the sleep-wake cycle of fish. The fish living near the surface of the water is more dependent on light as compared to the fish species inhabiting the bottom of the water.

Mexican Cavefish:

This fish species is habitual of living in caves without a tinge of sunlight reaching them. Thus, this fish has gone blind over time, and they can find their food without light.

Thus, fishes do not need to see the sun or require sunlight. Any alternate source of light is enough for fish to go on with their daily activities.

As long as fish is getting their food and sleeping on time, they do not care about the source of light used.

What are the benefits of sunlight for an aquarium?

Following are some benefits that you can achieve by providing constant sunlight to your fish.

Better Pigmentation:

Sunlight has proven to be beneficial in boosting the pigments and coloration in fish. The fish living near the surface of the water have better colors and improved pigmentation. As compared to the fish living near the bottom.

The Mexican cavefish is thus colorless as it is not ever exposed to sunlight.

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Temperature Management:

For the fish habitual of warm waters, sunlight is no less than a blessing. Apart from the light sun is also a source of heat maintaining a correct water temperature for fish to survive.

More Algae for Algae Eating Fish:

As mentioned earlier, excess light is responsible for the abundant production of algae. This alga is a food source for algae-eating fish species.

Thus, sunlight is ultimately useful for algae-eating fish.

Supply of oxygen:

Sunlight is a necessary component for photosynthesis and in turn production of oxygen. This oxygen is dissolved in water and is readily available to fish. Thus, sunlight is beneficial for fish as a source of oxygen.

What are the drawbacks of sunlight on the aquarium?

The downsides to the constant sunlight supply are more than the perks and here we will look at them individually.

Temperature Rise:

The excess light will result in an unwanted rise in the temperature of the aquarium. This increased temperature can put unnecessary stress on your fish.

Algal Bloom:

The greatest downside to excessive sunlight is unimaginable algal production. This algal bloom can destroy your aquarium in no time.

Changes in Circadian Rhythm:

Sunlight can put a negative effect on the circadian rhythm of fishes, resulting in disturbances in their normal sleep-wake cycle. Inadequate sleep can make your fish sick due to unnecessary stress.

What could be an alternate source of light for the aquarium?

LED lamps are the absolute alternative to sunlight. Lamps have unlimited advantages over sunlight, firstly, lamps have adjustable lights. You can even put a timer on the lights to switch off at any time.

Furthermore, lamps are sufficient for plants to survive and grow. They can be adjusted according to the needs of the plants and fishes to avoid unnecessary algal growth or a temperature rise.

In addition, the timer of lamps could be altered according to the internal clocks of fish to help achieve a perfect sleep-wake cycle for fish.

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Thus, lamps are a perfect substitute for natural sunlight.

Frequently Asked Question (FAQs):

How much sunlight do fish need?

Fish do not need sunlight, just a normal amount is more than enough. Excess sunlight could be hazardous for your aquarium ecosystem. Fish is pretty fine even without any sunlight available.

Do fish like sunlight?

Fish have no inherent liking or need for sunlight. Some fish species inhabiting the surface of lakes or oceans do need light for better coloration, but this need can be fulfilled by artificial LED lights as well.
Thus, fish do not like sunlight, nor do they dislike it. Fishes are fine either way until their needs are met properly.

Can a fish tank be near a window?

It is strictly prohibited by aquarists to place your aquarium near a window. Whenever looking for a perfect place for your aquarium try to avoid the locations having direct sunlight.
Placing your aquarium near a window will result in the overproduction of algae, turning your aquarium green in no time.

How long should I keep my aquarium lights on? 

The light should be adjusted according to the sleep-wake cycle of your fish. Normally, a period of 12-14 hours is more than sufficient for your fish in the aquarium.  


Thus, it is clear that fish has no biological need for sunlight. Fish do not need to see the sun and it is of no particular benefit to fish.

Plants do get a lot of advantages from continuous sunlight supply, but these perks can also be achieved by using LED lamps.

Fish really do not care about the source of light as long as their food requirements and sleep are managed.

So, in conclusion, sunlight is necessary for an ecosystem but not for an aquarium and especially not for fish.

Hope this article answered all your question and cleared all the misconceptions.

Best of luck with your aquarium!!!

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