If you’ve ever wondered “can fish see in the dark?” you’ll be interested to learn the complex answer.
While fish can’t see in the dark, they do have pressure-sensitive organs on either side of their body to help them navigate in deep water or at night. These are called lateral lines.
Notably, fish don’t experience light in the same way we do. Still, they can perceive wavelengths of light underwater, and they prefer to have light/dark cycles that represent night and day.
Are Fish Okay in Total Darkness?
Some deep-sea fish make do in total darkness, but aquarium fish need light. This is especially true for species that live in shallow waters close to the sun.
Light helps aquarium fish maintain their vibrant colors and boosts their immune system, similar to how sunlight and vitamin D boost ours!
Because most fish aren’t nocturnal, light also indicates that it’s time for your fish to swim, eat, and play. Light and dark indicate the day and night cycles that fish live by, just like they do for us.
If you were to keep your fish in total darkness, it would always assume it was nighttime, and would likely become stressed and/or sick.
Think of how you would feel if you were kept in total darkness all the time.
TLDR; per Kidadl, “experts suggest that fish should never be kept in total darkness.”
Are Fish Afraid of the Dark?
No. Fish may be startled by abrupt changes to the lighting in their tank, but they aren’t afraid of the dark.
Rather, darkness tells your fish that it’s night and time to sleep.
For nocturnal fish, the night is the only time they feel safe coming out of hiding to play and eat.
Do Fish Need Lights Off at Night?
Yes. Fish need 10-12 hours of darkness every day, so they have time to rest.
When the lights are off, fish enter a dormant state that is similar to sleep.
They ‘sleep’ with their eyes open and remain responsive to stimuli, like light. This is why it’s so important to keep the lights off.
Without 12 hours of darkness, your fish will be exhausted and lose interest in its surroundings. You may also notice your fish going into a trance-like state during the day.
Fish, like most animals, need day and night — and light and dark — to survive.
Even nocturnal fish need the lights off at night, so they know it’s time to come out and play.
Can Fish Be Fed in the Dark?
Fish will eat whenever they’re hungry, but they will have a harder time finding food in the dark.
Nocturnal fish, on the other hand, prefer to eat in the dark.
Ultimately, you should get to know your fish’s preferences and feed them accordingly.
For example, catfish and some plecos prefer to eat at night, but most aquarium fish prefer to eat during the day.
Rest assured, your fish will eat if it’s hungry, but you may have to deal with more uneaten food waste if you feed your fish at the wrong time of day.
Do Fish Like Aquarium Lights?
Aquarium lights can help you see your fish better and cultivate aquarium plants.
Nevertheless, each species has preferences when it comes to lighting. For instance, some fish don’t like bright lights, and almost all fish prefer lighting that mimics their natural habitat.
Whatever you do, remember to turn your lights off for 10 to 12 hours every day.
If you want to watch nocturnal fish, consider installing a night light or moonlight to observe them without disturbing their sleep/wake cycle.
Additionally, one thing all fish dislike is sudden changes to their environment.
Before turning on your aquarium lights, open the curtains or turn on the lights in your room so your fish has time to adjust.
When it’s time to turn the lights off, turn the brightest light off first and let the natural light fade away slowly.
If your fish lives in an office or another environment where lights remain on at all hours, you can simply cover your fish tank with a towel or blanket when it’s time for bed.
What Do Fish Do When It’s Dark?
Most fish sleep when it’s dark. Nocturnal fish, on the other hand, come out when it’s dark and hide and sleep during the day.
This way, day and night stay as constant as they do for you (even during daylight savings time).
In Summary: Your Fish Needs Both Light and Dark
Aquarium fish can sense their environment in the dark using their lateral lines, but most species can’t “see” in the dark, and all species need a light/dark cycle.
While fish see — and sleep — differently than we do, they can still perceive waves of light underwater, and light is still important to their well-being.
Similarly, fish need periods of darkness so they can rest.
Don’t worry — your fish isn’t scared of the dark, though they may be scared of sudden changes to their environment.
Turn on the lights slowly, and dim them naturally when it’s time for bed. Also, choose aquarium lights suited for your species of fish.
Make sure your aquarium lights go on and off at the same time each day and try to feed your fish at the same time, too.
If you need to feed a diurnal fish at night or a nocturnal fish during the day, know that your fish will eat whenever it’s hungry. However, be mindful of the mess.
At the end of the day, if you put your aquarium lights on a timer and feed your fish every day, there’s not too much damage you can do.
Don’t keep your fish in pure darkness, but don’t keep the light on all the time, either.
As always, set up your tank for the species of fish you are keeping, and you will be just fine!