Are fish affected by light

Are fish affected by light?/ Everything You Need To Know!

Everyone loves light, as it makes everything visible to us. It seems unlikely to live without light in the dark. However, what about fish? Are fish affected by light? Many fish lovers with aquariums in their homes, as well as fishermen, have asked me this question.

The answer is yes, there are a lot of behavioural and physical effects on all species of fish.

When fish are exposed to too much artificial light, it interferes with all of their physiological and behavioural functions. Light also affects the metabolism of fish.

That’s the quick answer. If you want to learn profoundly about this topic, then make sure you read this article all the way to the end so that you do not miss anything vital.

Now let’s discuss our topic without getting behind schedule.

Are fish affected by light?/ Everything You Need To Know!

Are fish affected by light?

The answer is yes, each species of fish is affected by light in both behavioural and physical ways. Overexposure to artificial light interferes with fish’s physiological and behavioural functions

The thing that light affects the most is fish metabolism. The growth and production of eggs may be significantly accelerated by increasing light. In several fish species, the amount and quality of light affect the maturation of the gonads.

It may be difficult for fish to develop properly and their regular metabolism may be affected if they do not receive the necessary amount and intensity of light.

The Question Is, What Are The Effects Of Light On Fish?

Light can have different effects on fish based on their life stage. Sometimes, the light can be a very good thing for them, while other times, it can be aggravating and annoying for them. 

It is therefore necessary to look at the different stages of fish life to understand how they are affected by light at each stage.

Effects Of Light On Fish Different Life stages:

Luckily, there has been a lot of research on the effects of light on fish, which shows the following effects on different fish life stages:

Good Effects On Some Fish Reproduction

16 hours of light and 8 hours of darkness benefited the growth and reproduction of cod (Gadus morhua), trout (Oncorhynchus mykiss), sea bream (Sparus aurata), and red snapper.

During this photoperiod, species with better feed visibility have higher feed consumption and feeding efficiency.

Bad Effects On Some Species!

A prolonged light cycle isn’t always the key to successful fish reproduction, especially when it comes to lighting on fish production.
Several aquatic species prefer short light periods, such as turbot (Scophthalmus Maximus), which convert feed more efficiently and yield higher yields under 12:12 and 08:16 light-dark cycles.


During the early stages of development in the catfish (Clarias gariepinus), prolonged exposure to light causes distress, which delays growth and increases aggression.

As a result, these effects have a direct impact on the survival of the catfish. Continuous activity and increased aggression in this same species kept under longer lighting schemes have resulted in elevated lactate and cortisol levels.

Are fish affected by light
Redtail catfish close up. Free public domain CC0 photo.

After prolonged exposure to darkness, the catfish’s dermis becomes dark, increasing its market value.

What about Goldfish?

Just like other species, goldfish also have some effects of light on them.  As goldfish don’t have eyelids, they rely on cues from their surroundings to determine when to feed, sleep, and be awake.

Therefore, goldfish are totally dependent on light. When it’s dark, the goldfish thinks that it’s time to go to sleep and stops eating and moving. And when it’s light, then goldfish tend to come out and start eating food and enjoying it.

Are fish affected by light
Free goldfish image, public domain animal CC0 photo.

So, these are the effects of light on the life of fish. It is evident that light effects vary depending on the species of fish and their life stages.

Is there a colour that fish are attracted to?

Due to their brightness and ability to attract fish from a distance, white and green lights are the colorus that fish are attracted to the most. Other than these two colorus, fish are also attracted to yellow.

How does black light affect fish?

Most people use black lights in their fish aquariums to heat them. However, it is not advisable to heat or illuminate a fish tank with black lights. It is important to provide aquarium lighting that mimics the natural lighting fish would encounter in the wild. 

Due to their UV properties, black lights should only be used sparingly. Black lights in the 315 to 380 nm range are the least hazardous.

But, what about UV light? Let’s talk about that now!

How Does UV Light Affect On Fish?

By encouraging the pigment to reproduce more quickly, UV light increases the fish’s natural tolerance levels to UV radiation. Goldfish’s color is also affected by how much UV light they receive.

Higher UV levels tend to result in vivid colors in fish, while lower levels tend to result in paler colors.

What To Consider About Lighting in An Aquarium?

When there isn’t any light in the fish aquarium, the color of the fish and the plants inside won’t look as beautiful and colorful, especially when the tank is placed in a dark area. Thus, lighting the aquarium is crucial.

As you can see, the fish can be affected negatively or positively by the light, so you have to make sure that you’re lighting the aquarium in a good way.

For that reason, I’m going to tell you all of the things that you must consider to ensure that the lighting in your fish tank isn’t doing any harm to them. So, let’s dive in!

1) Consider The Fish species!

Thousands of fish species exist around the world, as you know. So, the light requirements are different for all of them. Once you have chosen the species you want to house, you can better assess the lighting requirements.

Before choosing aquarium lighting, make sure it will provide the right kind and amount of light for the particular subspecies you plan to keep.

Obviously, you’ll do your own research, but to get you started, let me tell you what type of fish people usually get in their aquariums and their light requirements.

Most Common Species That You Might Get Home And Their Light Requirements!

Most of the species that people like to get for their aquariums come from rivers, clear lakes, and streams. Since these species of fish are more exposed to the sun, they’re used to living in the sunlight and the warming rays of the rainforest weather.

It is important, however, to provide darker areas when it is bright to accommodate fish that prefer to hide from the light. Plants and rock outcroppings provide a natural habitat for these fish.

But not all species are the same. Some species of fish like to live in a dimmer environment as well. So, please make sure that you’re researching enough about the species that you’re bringing home.

This will make it easier for you to decide what type of lighting you have to do in your fish aquarium

2) The Type Of Light Matters A lot

The type of light you’re putting in your fish aquarium matters a lot. The fish may react differently to it.

The most common lights that people always put in their aquariums are incandescent, fluorescent, or LED lights for fish. Is it true that incandescent light can be harmful to your fish?

Yes, they can be harmful because they may create too much heat in the water, especially in the area closest to the aquarium light.

Since fish can’t handle so much heat, they’ll avoid swimming in the hot part of the aquarium and will only swim in the cold one. But what about LED lights? Can you consider using them in your aquarium?

Yes, you can consider LED lights for your aquarium, as they virtually don’t create any heat in the water. The best thing about these lights is that they come in so many colors. This means you’ll be able to choose your favorite color.

3) Effects Of Lighting On Aquarium Plants

Plants, in addition to fish, contribute to the aquarium’s aesthetic appeal. Light is very important to plants, as it helps them remain healthy. Thus, you have to be aware of the amount of light required for the types of plants in your aquarium.

Just like fish, the amount of light required for plants depends on their type. Some types of plants need more light, while others need less. Considering some common plant types and their light requirements, let’s take a look at some of them.

Plants Light Requirement!

  • Tropical Plants: For proper photosynthesis, tropical plants require a large amount of light. In their natural habitat, plants that grow near water’s surface are especially susceptible.
  • Plants With Red Colors In The Stems And leaves: The light level must be very high for plants with reddish stems or leaves.

These are two common types of plants that people like putting in their fish aquariums. If you’re thinking of putting another type of plant there, then make sure you do proper research about the lights’ effects on it.

Also, see how intense light will affect the plant. This way, you’ll be better able to get plants that are suitable for the light of the aquarium and will make your aquarium look beautiful.

4) Day And Night Cycle Issues For The fish.

The animals that live in aquariums will be affected by a steady level of light in different ways. Using day and night lighting, aquarium owners can mimic the light levels found in a natural setting and replicate the light present in a species’ habitat.
Keeping an eye on nocturnal activities is made possible by moonlight, also known as “nightlights.” Tropical fish and plants are usually found in aquariums, which receive 12 hours of light daily.

For hobbyists, this eliminates the need to change their timers on a seasonal basis. If you want to make sure your fish receive light at the right time, you can use a simple timer that will automatically turn the on and off the light as needed. Sounds interesting?

A fish keeper should consider the seasons when changing from daylight to nightlight for aquarium specimens from northern and southern regions.

Moreover, if the family will be watching TV in the evenings, it is best to keep the tank out of direct sunlight and allow it at least 12 hours of darkness each day.

Fish keepers should consider the seasons when changing from day to night lighting when dealing with species from northern or southern regions.

In addition, to keep the lights on at night for the family’s entertainment, the tank should be kept away from direct sunlight and left in the dark for at least 12 hours each day.

5) Get The Lights That Bring Out The Colors of the Fish.

How would you feel if the lights you installed in the fish aquarium failed to bring out the color of the fish? Obviously, it won’t be good to see. What type of lights should you put in your fish tank to bring out the beautiful colors of the fish?

Bright lights are always preferred as they darken the pigments of the fish, making them look unique and eye-catching. What about the discus fish?

Will they like a bright tank? A lot of folks say that the discus fish don’t like a lit-up tank, which is absolutely wrong. They really like it, but in the beginning, when they’re not used to the light, they might not like it.

Because they’re not used to the light. But, after 4 to 5 days, they’ll start getting used to the light and start liking it. Their coloring will darken, and they will grow quickly. Isn’t it amazing to know how valuable lighting is for fish?

So, these are some of the tips for putting perfect lights in your aquarium that don’t harm the fish. 

I guess I’ve covered all the effects of light on fish. As a next step, let’s answer a few frequently asked questions. Let’s begin!


1) Are fish affected by light?

Yes, light affects the development, psychological, and physical functions of fish. The effects of the light can be positive or negative depending on the fish’s species and life stage.

2) Is lighting stressful for fish?

In order to sleep, some fish need complete darkness; otherwise, they may become agitated or stop eating. A lot of fish species are strained by too much light, which causes them to compete with each other.

3) Is light stressful for fish?

Artificial nighttime lighting is predicted to result in fish being more stressed, leading to higher cortisol production.

Final Words:

Are fish affected by light? Yes, light affects the development, growth, and behavioral and psychological functions of the fish. It can also disrupt the spawning of migratory fish. The effects of the light can be both negative and positive, depending on the species of fish.

So, that’s all I had for you in this article. I hope now you’re aware of all the effects of the light on fish. Still, if you have any questions related to the topic, please let me know in the comment section below. I’d love to help you out.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *