Can Tetras See In The Dark? (Is It Ok To Keep Them In Dark?)

Image of a tetra swimming in the dark

Although light is essential for fish to see, you must note that some fish species live below the photic zone. Fish living in the depth of the sea have evolved to navigate without light. So just like fish from the deep ocean, can tetras see in the dark?

Tetras can’t see in the dark. Although they are found under the dense forest vegetation, some amount of light passes through to the tetras that they use to see things around them. Tetras rely on light to find food like worms and small crustaceans, avoid being eaten by a predator, and locate mates.

Having said that, is it okay to leave them in the dark?

Is It Okay To Leave Tetras In The Dark?

Tetras don’t require constant exposure to light.

So, if you keep your aquarium lights off overnight, your tetras won’t notice anything different about their environment and may utilize the time to rest.

If the tank lights are on for 24 hours, it will increase the water temperature and promote rapid algae growth.

This is not only an ugly sight to watch, but it can lead to health issues for your aquatic pets.

As the algae blooms and busts, it releases toxins into the water. Some of these toxins can cause illness in your tetras.

For example, blue-green algae produce cyanotoxins while red tide produces a neurotoxin.

Both of these toxins can kill your tetras.

Tetras need a period of darkness, following the 12 to 14 hours of day cycle.

The darkness at night allows them to nap, rest and regroup to perform activities on the following day.

Recommended Further Reading:

Do Tetras Need Light At Night?

Like humans, tetras are diurnal and need to rest at night.

It means that when the sun goes down, so should the lighting inside your tank.

This will ensure it doesn’t affect their circadian cycle.

Keeping the aquarium lights at night will not allow the tetras to get the much-needed rest.

In addition, it can be detrimental to the health of your aquatic pets as it may increase their stress level and result in loss of appetite.

Consider using dimmable bulbs to provide enough light during the day but still let the tetras sleep at night.

These bulbs emit less heat than regular incandescent bulbs and also last longer.

You could also try placing a black sheet over the top of the aquarium to block any incoming direct light.

Do Tetras Need Complete Darkness?

Tetras need complete darkness to rest and regain their energy after a whole day of activity. Darkness helps them recover from exertion. They will find a quiet spot at the tank’s bottom or around the decoration to rest in the dark.

It’s helpful if you leave your aquarium lights on during the daytime and then switch them off at night to mimic a typical day’s light and dark cycle.

Another reason to provide complete darkness at night is to ensure the circadian cycle of tetras is complete.

In addition, it will ensure that your aquatic pet’s body processes are complete at various points within 24 hours.

Related Further Reading:

How Much Light Do Tetras Need?

Tetras should have some amount of natural sunlight every day. However, they don’t need light all the time.

If you use fluorescent tubes instead of LED lamps, you’ll need to adjust the intensity accordingly.

The length of time depends on how bright your aquarium lighting is.

A good rule of thumb would be to set up your aquarium lights directly over the surface of the water.

It’s best to keep the light on for 12 to 14 hours during the day.

A proper sleep-wake cycle is necessary for your tetras to remain active and healthy.

Furthermore, besides nutritious food and good quality water, aquarium owners must create a conducive environment to support the healthy growth of their tetras.

Can Neon Tetras See In The Dark?

Just like all other tetras, neon tetras also cannot see in the dark.

However, neon tetras can see if there is some amount of light available in the water.

Moreover, like other tetras, neon tetras also need to complete their circadian cycle.

It’s a good practice to follow the day-night cycle mentioned above when caring for your neon tetras.

Besides, neon tetras are diurnal. Thus, they remain active during the daytime and rest at night to recover from exertion.

Interesting Further Reading:

Things To Remember

  1. Tetras are diurnal and need to complete the circadian cycle to ensure longevity.
  2. Proper rest at night will allow them to recover from exertion and lead an active life.
  3. The aquarium lights should be in sync with the day and night cycle.
  4. The presence of aquarium lights 24/7 may increase water temperature, which favors algae growth.
  5. Algae bloom and busts can be dangerous, as toxins released in the water can suffocate the fish.
  6. Creating a conducive and sustainable aquarium environment will ensure the good health of your aquatic pets.


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