It is common among goldfish owners to have doubts about whether or not to keep the aquarium lit up at night, this doubt arises because of the question, do goldfish see in the dark or not?
Can Goldfish See In The Dark?
The short answer is no. Although they have good eyesight, goldfish cannot really see in the dark.
In spite of this, the eyesight of goldfish is quite developed, even in some cases, their eyesight could be better than ours since they have four color receptors and we have only three.
The fourth receptor allows them to see ultraviolet light; also, they are very sensitive to polarized light, which gives them the ability to perceive contrast in an image.
Even so, they do not have such wide depth perception; in fact, the goldfish see their surroundings clearly for about 15 feet and their vision is not as sharp as that of humans (which is 60 times sharper).
Goldfish Use Their Sense Of Smell.
Since they cannot see in the dark, goldfish use their highly developed sense of smell to swim and orient themselves in the aquarium at night, avoiding bumping into each other or the aquarium decorations.
Lateral Line System.
In addition to smell, goldfish also use a lateral line system as an alternative to sight. This is a sensory organ that some marine animals have that serve to detect the movement and vibrations of the surrounding water.
This helps goldfish avoid collisions, orient themselves in relation to water currents, and locate prey. It also allows them to detect movement and hide from predators.
Goldfish Can’t Live In The Dark For Too Long
As we could see, goldfish know how to deal with the darkness with different alternatives, but this does not mean that they can live in the dark for a long time, as they cannot get used to it.
The goldfish is a diurnal fish.
Goldfish needs, therefore, to have cycles of light to stay healthy, to eat and to be active but also darkness to be able to sleep at night.
It should receive approximately 8 to 12 hours of darkness, as they do not have eyelids; their eyes are kept open, so they need darkness and calm to be able to sleep.
But as we mentioned, they can live in darkness for too long, in fact, they can lose their characteristic golden color and turn white when they do not receive any light for too long.
If the fish are in the dark for a long period of time, their production of pigments slows down causing the colors of their body to fade.
On the other hand, if the fish is exposed to light more than necessary, their sleep cycle will be interrupted, they will stop eating and will not be able to sleep and this could cause them stress, which could lead them to death.
In conclusion, even though it cannot see well, the goldfish can do very well in the dark with other alternatives when it needs to, and just like us; it needs the benefits that both light and dark offer.