My aquarium used to be located in my bedroom, and a couple of years ago I brought home two goldfish. They were my first fish ever, and I found it crucial to provide them with the best care possible. At night, all lights were off, and I wondered whether this was fine for my goldfish. Since then I did a lot of research and know the answer.
No, goldfish are not able to see in the dark. During daytime, goldfish roam the waters with great eyesight. During the night, they rely on their excellent sense of smell. They also utilize their Lateral Line Organ (LLO) which accurately senses vibrations and water movement.
Now that you know the short answer, it’s important for you to learn the basics concerning light and dark around goldfish. There are some interestings aspects that simply can not be overlooked when aiming to take good care of your fishy friend. In the rest of this article I’ll briefly cover exactly what you need to know.
How good is the eyesight of goldfish?
According to an article on cuteness.com, the eyesight of a goldfish could be called superior to that of a human. You see, we humans are able to pick up on three colors with all their combinations: Red, Green and Blue (RGB). Any combination of these three colors make up every color you’ve ever seen.
Goldfish, on the other hand, can see light in a spectrum we are not able to: ultraviolet. Next to the three colors we’re able to see, goldfish are sensitive to polarized light. This makes their vision superior to ours in this aspect.
However, we humans are able to see long distances in excellent resolution. I personally need some glasses, but let’s not mention that. Goldfish are able to see clearly for 15 feet, or 4.5 meters, before things turn blurry.
This is why a sudden movement away from the tank can startle fish, whereas elegant movement within the range of clear-goldfish-sight seems to calm the fish.
How does a goldfish navigate at night?
At night, goldfish are not able to use their decent ability to see. However, they’ve worked their way around this by developing a great sense of smell. They can use this sense to navigate around the aquarium, but what’s more impressive is their so-called Lateral Line Organ or Lateral Line System.
Together with the inner ear, the Lateral Line System is often referred to as the Octavolateralis system. I’ve got to admit I found this information on Wikipedia, which in turn referred to a scientific article that goes further into depth.
But what’s the actual use of these fancy-called parts in a goldfish? Well, they make the goldfish extremely sensitive for vibrations and help detect movement or pressure in the surrounding water. Because the goldfish has developed these functionalities to a rather accurate and functional point, you could even say that goldfish indeed are able to see at night, just not with their eyes.
Well in that case goldfish should be able to live in the dark
While goldfish do know how to make their way around the tank at night, goldfish would not be able to live in the dark for a prolonged amount of time. There even is evidence that goldfish lose their color when there’s not enough light. One of my goldfish lost all its beautiful colors and turned white, probably because my aquarium light was not bright enough.
Next to losing its color, goldfish can under no circumstances get used to continuous darkness. Just like we rely on a healthy alternation between daytime and nighttime, goldfish need this to stay sane. Goldfish need a light period and a dark period, and if they lack either they will get stressed to a point where they become unhealthy and can potentially die.
This means that goldfish are unable to live in continuous darkness, but they are also not able to survive in a light environment for many many days.
By adding an aquarium light and having a timer control regular periods of “daylight” and nighttime, your goldfish will develop and keep a healthy rhythm in which it eats during the daytime and sleeps at night. While being able to easily navigate the waters in darkness, the goldfish does take time to sleep.
How much do goldfish sleep at night?
We already concluded that goldfish sleep at night, but did you know that these fish do not have eyelids? They are left to the surrounding brightness in order to find a quiet and dark place to sleep. The fish will hover around 3 inches (8cm) above the water substrate with its head slightly tilted down.
There are even some videos available online that will show you the way these pretty fish sleep at night. While it’s an ancient video all the way from 2010, it’s still great to see the way this fish sleeps.
Can a goldfish see outside the tank?
If you’ve been keeping goldfish for a while, you know how enthusiastic they react when you’re about to feed them. They are almost begging for food, because these fish learned that you can be enticed to feed them. That’s actually pretty smart! But for this, they must be able to see outside of their aquarium
Yes, goldfish are able to see outside the tank. They’ve got great eyesight which allows them to scan for movement in the room of the aquarium. The further away the movement is, the worse their vision is, meaning they’ll be able to see less clearly.
When you’re directly in front of the aquarium, they definitely can see you.
When you press a finger against the glass, trying to get the attention of your goldfish, they often try to bite on it like it’s food. This is an extremely common goldfish reaction. If you were to ask me whether your goldfish can actually recognize you as being its owner, I would probably have to disappoint you. Goldfish are not able to tell the difference between their owner and other people.
There is evidence that archerfish are able to tell apart human faces. It’s an interesting read by nature.com, and if you’re really into this I would recommend giving this article a read.
I want to take some time to answer some more basic questions that are truly important when it comes to keeping goldfish in a safe and responsible way. If you care about the way your fish live, it’s best to check whether you already know the answers to the next questions.
Can you feed bread to your goldfish?
An important question that many people often ask is whether it’s alright to feed bread to your goldfish. It must be said that goldfish aren’t the smartest fish and they will most definitely eat bread when you feed it to them. However, don’t. Bread can act as a sponge, sucking up water and swelling up, causing serious constipation to your fish.
Bread can really block the intestines of your fish, so at all times refrain from feeding bread. It really is something you should not do, no matter how excited your fish get when you feed it to them.
I’ve written a more detailed article about feeding bread to fish, as well as what some alternative food can be. If you’re interested, check out that page here.
Can goldfish hear?
While a goldfish obviously does not have ears like we do, they are still able to pick up on sounds. In their inner ear there are highly sensitive parts that can pick up vibrations and translate them to electric signals. Hearing together with the Lateral Line Organ we just discussed, forms the Octavolateralis system of a goldfish that’s used to sense vibrations, pressure and movement in the surrounding water.