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Do Fish Need Light at Night

does fish need light at night
Caring for fish requires all sorts of equipment. You need a spacious aquarium, a filter, excellent plants, gravel, and light, among many other things. Keeping the fish happy and healthy is on the line, so you should know when these things are necessary and when they are not. One crucial question to ask is, “Do fish need light at night?” The short answer is no, fish don’t need light at night.

Fish don’t need light at night, and here are the reasons why.


Reasons Why Fish Don’t Need Light at Night

The reasons why fish don’t need light at night are:

  • Fish need a light cycle that mimics the typical daylight and nighttime hours
  • An irregular light cycle stresses out fish
  • Extreme algae growth
  • Adverse effects on plant life

Let’s discuss these factors in detail.

Fish Need a Light Cycle that Mimics Daytime and Nighttime Hours

Most aquarium fish such as bettas, Glofish, Bolivian, and German blue rams need light only during the day. Why? Aquarium fish have an active and inactive cycle based on the typical daytime and nighttime hours, just as humans do.

When the light does not turn off at night, the fish get confused about daytime and nighttime. Their sleeping patterns get scrambled, and their health goes down. They become prone to diseases, which leads us to the second reason why they don’t need light at night.

An Irregular Light Cycle Stresses Out Fish

An irregular light cycle or constant exposure to light day in and day out will stress your fish. They don’t know when daytime and nighttime are. They don’t know when to be active and when to rest. To them, each second is daytime.

Light plays an integral part in the circadian rhythm. The circadian rhythm is the program of sorts responsible for the release of melatonin, which induces sleep. When the body is exposed to light, the circadian rhythm thinks it is day and not time for rest or sleep.

The longer the fish are in constant light, the more confused and stressed they would be. Eventually, they will lose their vibrant colors and become sick. Death is a possibility if such conditions continue.

Extreme Algae Growth

Algae needs light to grow. Exposing your aquarium to light twenty-fours every day will expedite algae growth. Too many algae, in turn, is bad for the health of your fish. The most problematic thing about algae overgrowth is oxygen depletion.

Algae consume oxygen to live. If there are too many algae in the tank, the fish might not get enough oxygen, which leads to diseases and other problems.
Adverse Effects on Plants

If you have plants in the aquarium, it is necessary to have a light, especially a grow light. Light helps plants grow because it is essential for photosynthesis. However, plants also need a light cycle as fish do.

Like fish, plants need a light cycle that simulates the daytime and nighttime dynamic. They need around twelve hours of light and other twelve hours of darkness to rest.

Do fish need light at night?

For several reasons, no, they don’t. Constant exposure to light will inevitably cause sickness and potentially death to your fish. But what if you have nocturnal fish?

What If You Have Nocturnal Fish?

fish dont need light at night

Does having nocturnal fish change the approach you should take regarding aquarium lights at night? Not necessarily. In the wild, nocturnal fish function without a big bright light shining on their surroundings. These fish can still function normally without a bright light at night.

However, some good arguments support having a night light for your fish. Those reasons are:

  • Enhances visibility in the aquarium
  • Expedites fish pigment darkening

Let’s discuss these factors one at a time.

Enhances Visibility in the Aquarium

A night light will help you see the fish even at night. Seeing the aquarium at night is essential because some fish species only do some activities at night. Examples of such activities include breeding, aggression, and other nighttime behaviors.

If you have nocturnal tenants in your aquarium, it’s best to see what they do at night. Some nocturnal fish species have an aggressive opinion towards diurnal fish (fish that are active during the day).

Additionally, a night light will help you see some mating and breeding behaviors. Livebearers such as guppies, for example, like to have their offspring at the early hours of dawn. Damselfish and tetras are other examples of laying their eggs at night.

Expedites Fish Pigment Darkening

Light darkens the pigments of organic things (plants, animals, and even humans). Constant exposure to light will help bring out your fish’s color faster. If an attractive and vibrant aquarium is a big deal for you, leaving a night light on must be appealing to you.

What Light is Best for Nighttime

The best option to get all the benefits of a night light but without its disadvantages is blue light. Blue light lets you see what’s going on in the aquarium at night and helps bring out the fish’s color faster. But it does not mess with the circadian rhythm of the fish, promote algae growth, or affect plants. It is the perfect solution!


Do fish need light at night? No, fish don’t need regular light at night. However, if you want to see your fish’s behavior at night or increase their color development rate, you can use blue light. Blue light does not affect your fish’s sleeping pattern and health. It does not promote algae growth nor has adverse effects on aquarium plants.

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