Can Goldfish See in The Dark?

Goldfish is probably the first choice for any beginner fish owners. The vivid color and shape of this species attract people quite easily. There is another interesting thing about this goldfish, their eyesight. Goldfish has pretty sharp eyesight, and in some cases, it can surpass the eyesight of humans.

But what about their night vision? Can goldfish see in the dark? Well, in this article, we will discuss the goldfish eyesight and its capability to see in the dark.

We, humans, can see up to a mile pretty clearly, depending on our eye condition, whereas goldfish can only see up to around 15 feet. So your sudden movement out of that 15 feet from your goldfish can put it in stress. Then how do goldfish protect themselves from the predators? Well, for that we need to have a basic idea of the science behind fisheseyesight.

Fishes’ Eyesight

Different species have different sensory systems. Fish eyes are similar to any other mammals’ eyes, but just with one exception. They have more spherical eye lenses than humans or birds.

We see different color spectrums. For example, human sees the magical combination of color RGB, which stands for Red, Green, and Blue. We can only see this color and the colors made from the combination of these.

On the other hand, fish can see this RGB as well as UV light. And the ability to see UV lights aids them to see polarized light. So fishes, in some cases, have the upper hand in terms of eyesight than humans.

UV Light and fishes’ vision

A fantastic trait for many fish is that their visual pigment is capable of absorbing UV wavelengths. To see things in UV light, they absorb UV light. The ability to see UV light aids them in communication, survival, and mate selection.

Some fish has more blessed eyesight, and they can see beyond the UV spectrum. But the UV light is not a permanent part of fishes’ eyesight. As they turn old, they tend to go into the deeper water, away from the range of the predators, where there is very tiny or even no UV light.

Adjustable Vision

Some fish, such as the Hagfish and their predecessors are known for living into the very deep of the ocean. It helps them to survive from the predators because the light is very low down there. As a part of the adaptive vision, these fishes have grown a primitive eyespot. These eyespots decrease their necessity of having developed eyes.

Again, most fishes in deep water have comparatively convex eyespots. The convex lenses have the capability of gathering more light than the concave lenses. It helps them to see clearly even in shallow light makes them suitable for the environment.

Polarized light

As we have already known, UV light makes some fish sensitive to polarized light. Goldfish are among them. Polarized light is quite existing while the sun sets or in the morning.

This polarized light helps goldfish to see another fish in a blurry background. Also, it helps the schooling fishes to navigate, to show displays of the neighboring fish.

Many fish uses polarized light to aid communication. Detecting predators or preys by avoiding reflections is possible due to this polarized light.

Your aquarium fish use polarized light even to recognize you! Have you noticed how they react while feeding them? It is because of the polarized light on a bright sunny day.

Can goldfish see in the dark?

No, goldfish cannot see in the dark. Then the question comes, how do they move at night, or how exactly they survive from the predators? Or how do goldfish know if they are in a tank?

Well, the goldfish has a very keen sense of smell. By this fantastic sense of smell, they can feel minimal changes in the water while swimming past them. Their lateral line system” aids them to sense the changes from vibration in the water. So, not being able to see in the dark is not that big of a hazard for the goldfish.

Importance of darkness

Just because your goldfish can not see in the dark, you should not keep the lights on throughout the night. Like other mammals, goldfish need a dark environment to sleep.

If you turn the light on for the whole night, goldfish will get confused to understand whether it is daytime or night time. This, in some cases, can harm their health because their body will not act accordingly.

The goldfish have eye receptors that work like ours one. As the light becomes low, the resolution decreases, and luminance controls the most part of eyesight. This is the time when they are at the most risk of being attacked by predators.

The goldfish that live in the outdoor pond have much healthier eyesight. Because we tend to switch the aquarium light on and off too frequently, the tank fishes have comparatively weaker eyes.

How much light does your goldfish need?


The amount of light for your goldfish depends on some factors.

For a smaller tank, where you keep artificial plants, only need enough light to differentiate between day and night. For this, 1 to 2 watts per gallon water in supremely good.

On the other hand, the live aquarium plants need more light because they need to run their photosynthesis. For this large tank with the live plant, you should consider 2 to 5 watts of full-spectrum light per gallon of water.

Here the full spectrum of light is necessary. It contains both blue and red wavelengths, which are important for photosynthesis. Also, there is an RGB combination necessary for seeing things.

Your goldfish need 8 to 12 hours of darkness each night, to maintain the natural balance and sleep cycle.

Too little light is also harmful to your goldfish. For the lack of lights, your goldfish will mess up its sleep cycle and eating habits, hence causing health issues. Again, if the aquarium is kept in too much dark, your goldfish might turn pale, translucent like white in the worst-case scenario.

If your tank has live plants, they will also die because of the lack of light. Remember, light is mandatory for their photosynthesis by which they produce their food.

Last words

Your goldfish can not see in the dark. But they can sense every tiny detail. So leaving them with the lights turned on is not recommended. It will rather disturb the cycle and eating habits of your goldfish.

Your goldfish has enough strong smell sense to survive in the dark. Throughout the article, we have tried to enlighten you about “Can goldfish see in the dark?” We hope you found this helpful. Now it is your turn to provide it with everything it needs. Thus it will live a happy life and will interact with you!


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