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Do Aquarium Fish Need Sunlight? (Why + Why Not)

Do Aquarium Fish Need Sunlight? (Why + Why Not)

Most living creatures need light to live! The same goes for fish. However, do aquarium fish need sunlight, or can they survive on artificial light alone?

While many would argue that there are many things we’ve taken from animals we keep in captivity, modern technology has helped us improve their lives in many ways. 

There are many ways in which we have substituted sunlight. Artificial lights are enough in most situations, but what about the living conditions for aquarium fish?

If you want to know do aquarium fish need sunlight and whether you keep your tank close to your window, you’re in the right place!

Let’s get started.

Do Aquarium Fish Need Sunlight?

Some people are claiming that sunlight is the only type of light suitable for fish. Is this true?

The short answer is: No, your fish don’t need sunlight in order to survive or even to thrive. In fact, there are many downsides to keeping your tank in direct sunlight. 

The main issue is that direct sunlight can lead to algae growth. In fact, sunlight is the main cause of algae in a tank. 

Sunlight is a strong light that contains a lot of energy. Algae love this as it can help them thrive. 

Having too much algae is bad for several reasons. Most importantly, algae can use too much oxygen from your tank, leaving nothing for your fish. This can result in the death of your guppies, and other tank inhabitants. 

So, if you’ve wondered whether aquarium fish need sunlight, now you know that they don’t.

Is Light Necessary?

aquarium fish on sunlight
Photo: ethanscapes

While sunlight isn’t necessary for your tank, this doesn’t mean they don’t need a light source. Quite the opposite – light is necessary for all living beings to thrive.

From microbes to plants, fish, and shrimp, all creatures inside your tank require light. One of the main reasons behind this is photosynthesis.

Aquarium plants cannot live without photosynthesis. This process helps them live and grow. Not just that, but it helps your fish live and grow, as well!

When plants photosynthesize, they create oxygen fish need for breathing. At the same time, they’re reducing the amount of carbon dioxide which can be toxic to fish, shrimp, and other creatures.

Even if you don’t have live plants inside your tank, you still have plenty of beneficial bacteria! Having these bacteria is a good thing, as they eat ammonia and nitrite. Without light, these bacteria cannot survive, which means your fish are done for!

Not just that, but algae photosynthesize, as well. While too much algae is a terrible thing, having a tiny bit of algae is extremely beneficial. However, they too cannot survive without light.

But What About Fish?

Humans need sunlight to produce vitamin D and to ensure healthy bodily functions. Are fish the same?

Unlike most land creatures, fish don’t have a biological need for light. Their natural habitat is pretty devoid from light, so technically, they don’t need it to survive, at least not directly. 

However, as the water quality quickly becomes poor without the light, you cannot expect to keep fish in a tank that doesn’t have any light source.

There is one single fish species that we can keep in our tanks that doesn’t require any light, and that is the blind cave tetra.

These fish live in dark caves and are almost entirely transparent, and light will stress them out and harm them.

Other than blind cave tetras, all other fish require some amount of light.

How Much Light Do Fish Need?

harlequin rasbora

The exact amount of light depends on the type of tank you have.

In general, 8 – 10 hours of sunlight is enough for most tank setups. For reef tank setups, you need to have a bit more light – about 10 to 12 hours is enough.

Of course, you need to think about all tank inhabitants. Plants don’t have the same light requirements as fish, and some bottom-dwelling creatures might need less light than fish that like to swim near the top of the tank.

Also, keep in mind that too much light can cause more harm than good. I’m not talking only about algae growth.

Many fish are shy or nocturnal. If the tank has too much light, they’ll be stressed out or start hiding. 

Benefits of Sunlight

Since plants need light, sunlight has to be better than artificial light in some aspects, right?

In general, there are no benefits that sunlight has over artificial light. However, we can talk about the benefits of having a strong, bright light in your tank, as sunlight certainly is one.

Some of these benefits include:

  • Brighter color of plants and fish that live near the surface of the water.
  • Easier temperature management for tropical tanks.
  • Algae eating fish will love having more algae in their tank.
  • As plants will produce more oxygen, your fish will thrive.

Downsides of Sunlight

As I’ve mentioned before, there are many downsides of having direct sunlight in your tank.

I’ve already spoken about algae growth. However, this isn’t the only flaw of having too much sunlight. Here are some cons that you can also expect:

  • If you’re having a tank that doesn’t require warm water, the temperatures can become too high.
  • Direct sunlight can mess with the fish’s circadian rhythm.
  • Your fish can become stressed out.

What Happens If Fish Don’t Have Enough Light

Without the proper amount of light, any live plants you have in your tank will struggle to photosynthesize and die. The same will happen to any algae inside your tank. 

Not just that, but your fish can become sick rather quickly. Without algae and beneficial bacteria, the water will no longer be good for them. They will deplete oxygen reserves rather quickly and they’ll be more susceptible to harmful bacteria and parasites. 

As the fish’s immune system weakens, they’ll become more prone to illnesses and diseases. 

The same awaits not just your fish, but also any other animals you might have, such as shrimp or snails. 

As your plants and beneficial bacteria die, the pH levels of your water will likely drop. No method for raising the pH level of your tank can help you now! You need light to keep the good bacteria in your tank.

Some of the symptoms that there isn’t enough light in your tank include:

  • Your plants aren’t thriving or are dying.
  • Fish are gasping for air at the surface of the tank.
  • Fish seem as if they’re having breathing issues.
  • Your animals are refusing to swim as they don’t have enough strength. 
  • Tank animals are refusing to eat.

If you don’t deal with this issue right away, all of your tank inhabitants will likely die.

What Type of Light Is the Best?

small planted fish tank with fish

Most types of light are suitable for a tank. This includes standard fluorescent, full spectrum, LED, or even metal halide!

Most experts claim that LED lights are the best choice for an aquarium. This is also my favorite option. They are cheap, don’t emit any heat, and they come in various shapes and sizes!

Of course, you need to have your own tank in mind when choosing the best light for your fish. The most important feature to consider is the depth of the tank. Deeper tanks require brighter, stronger lights than shallow ones.  

For example, a bottom-dwelling sexy shrimp in a deep tank will need less light than a molly that swims around your tank.

Also, make sure that your light has a protective cover. If you’ve picked a light source without one, buy a glass canopy. This will keep the tank from overheating while diluting the light, making it more suitable for the creatures in your tank. 

Of course, if you can provide your fish with filtered sunlight, then there’s no real need for any type of light whatsoever! However, it can be challenging to determine just how much light your fish are getting this way. This is why artificial lights are preferred. 

Do Fish Need Light at Night?

The main reason why fish need light is to see. However, in nature, there is no light source during the night. As such, no, your fish do not need light at night. Quite the opposite – they’ll prefer having a day and night cycle similar to the one they’d have in nature.

Fish need to sleep, as well. Just like us, they sleep during the night, when it’s dark outside. If there’s too much light during the night, they’ll have trouble sleeping, which will stress them and possibly lead to health problems.

If you’re concerned about your fish not being able to see during the night, you can buy them a special night light.

This type of light can help them stay oriented during the night, without disrupting their sleep. Night light is similar to the moonlight, providing them the most natural living conditions possible.

However, you only truly need night light if you keep your tank in an area that is pitch black during the night, such as in a basement.

Final Words

While many people wonder do aquarium fish need sunlight, the truth is that artificial lights can provide more benefits. 

Sure, fish that live in nature live in direct sunlight. However, they live in huge bodies of water, while our tanks are several dozens of gallons at best! The bright sunlight is too much for fish in aquariums to handle.

In the modern age, there is no need to risk the health of your fish by keeping them in direct sunlight. LED lights are inexpensive and beneficial and you can find the one that will suit your tank the best.

Of course, you should never forget about the light entirely. Without light, your fish will die. Provide them with the best possible conditions in a safe way.