Do Fish Need Light At Night (Keep your aquarium natural)

Do Fish Need Light At Night

Many new aquarists are unsure whether fish need light at night. They have their new tank, which will often come with a light tube built into the tank, and all logical thought goes out of the window.

This is not the beginner’s fault as they want to do things just right and us human beings, well we use light at night so why shouldn’t a fish? Let’s look at why you have a light in your aquarium and whether you even need it.

Fish do not need light at night because, in the wild, fish are used to a period of daylight and a period of darkness. Too much light and your fish may become stressed and struggle to sleep. Some fish are nocturnal and prefer to eat when dark. Excessive light will also encourage algae overgrowth.

When setting up a new tank, remember that your aim is to set up an environment that will closely resemble a fish’s natural habitat. All living creatures are used to a 24-hour cycle of both day and night. Dependent on whether the species live in the Northern or Southern Hemisphere will dictate how much light and dark they would expect in every 24-hour cycle.

Unnatural light is a human invention, and constant light will upset a fish’s natural biological clock or circadian rhythms and often induce a stress response.

It has been found that many fish have developed circadian rhythms which directly impact the production of such things as melatonin, which fish have a higher level of at night and significantly lower during the day. The circadian rhythms control many things, such as a fish’s behavior, level of stress, general health, and even the development of new embryos.

Do Fish Need Sunlight

Aquariums, in general, have some form of lighting setup built-in. The bulbs are mostly of a standard type and do not emit ultraviolet rays like the sun, so do fish need sunlight, or will a standard light suffice?

Sunlight or ultraviolet light is not necessary for fish to remain happy and healthy, and although small doses are thought to be beneficial, larger doses will harm your fish. Most aquarists use larger doses of UV light to help sterilize the water in an aquarium and kill off any parasites before adding fish.

Your fish will be more bothered about how much light they get throughout the day, and by turning the light off at night, you will allow your fish to rest peacefully.


Be aware that some fish may be averse to strong light, so it is always wise to check the particular needs of any fish that you keep.

Both freshwater fish and marine fish will need around 12 hours of light each day. Not enough light, and you may start to notice their colors fade. Your fish can become lethargic and may stop eating.

If you keep your aquarium lighting cycle natural, you will, in turn, observe the most natural behavior from your fish, both during the day and at night.

If you have a fish tank with access to sunlight, you should make sure that your tank is kept away from direct sunlight. When sunlight passes through glass, it becomes magnified and will generate more heat, which will warm the water of an aquarium significantly.

Do Fish Need Sunlight
It is always wise to keep your aquarium away from direct sunlight.

Ultraviolet rays are largely filtered out when passing through glass, so they are unlikely to pass through your window and then your fish tank glass, but during the summer months, a fish tank can become much too hot, far beyond the temperatures your fish will be used to.

Unlike in the wild, where fish can swim deeper to escape the heat, instead, they will have nowhere to go and will probably die. Overnight, the tank will cool drastically, and these swings in temperature will not be good for any fish.

If your fish tank can be kept away from direct sunlight and still get enough natural light from a window, an internal light will not be necessary. I prefer to use tubes as they are designed to give the right amount of light, and I will use them in conjunction with natural sunlight.

When fish get enough light, it will help bring out their vivid colors. My aquariums have always been planted, and plants need light to keep them healthy and to aid in keeping your tank oxygenated.

Aquarium water can hold more oxygen when cooler, so too much sunlight can reduce oxygen levels. Another problem caused by too much light is algae growth (Algae Bloom).

Algae in fish tanks can lead to lower oxygen levels and higher carbon dioxide levels, which in turn may cause undue stress to your fish.

Plants absorb carbon dioxide during the daylight hours and convert it into oxygen, a process known as photosynthesis which is extremely beneficial to your tank. During the night, your plants will absorb oxygen, but as night time hours are shorter, this will not have much of an impact.

Do Fish Need Light To Eat

Fish generally don’t need light to eat because they have excellent eyesight in the dark. Mixed with their incredible sense of smell, a fish will eat quite easily in both light and dark environments.

Some fish are more nocturnal and prefer to eat at night, relying on their senses and good eyesight. They may enjoy hunting live foods such as Scuds, which will be much easier at night as the fish rely on stealth.

If you enjoy river or coastal fishing, you will know that night time fishing will often yield the best results as fish will feed much more aggressively than they will in daylight.

Do Fish Need Darkness To Sleep

Fish don’t need darkness to sleep, but if you want the best from your fish, providing them with the most natural cycle will help.

Fish will feel more relaxed in the dark as their instinct to watch for predators or other dangers will be less intense and will help them to sleep better.

Fish are pretty close to the bottom of the food chain in the wild and need to be alert most of the time, so a few hours of darkness will be very welcome. Providing hiding places within your aquarium will also help fish to seek shelter when sleeping.

Depending on the species of fish you own, they may sleep on and off throughout the day and night, so it would be wise to research the natural behavior of the fish you own to understand their individual needs better.

Wrap Up

Lighting is essential in an aquarium for many reasons. It influences the growth of plants and the behavior of the aquarium’s inhabitants and allows us to observe the tank at its very best.

I will soon be adding an article based solely on aquarium lighting and the different types of lighting that is available.

Hopefully, by reading this article, you can take away that lighting is not a difficult subject to understand and is often overthought. Yes, lighting can be much more complex, but by following some common sense, you will not harm your fish, and they will be perfectly happy.

If you ask yourself such questions as “Do fish need light at night?” or “Do fish need light to eat?”, ask yourself how they would cope in the wild, and I am confident you will answer your own questions.

Happy Fish Keeping!

Jon O'Connell

I have kept both marine and freshwater fish and set up almost 100 aquariums. Happy to share my knowledge and experience to help others enjoy keeping healthy and happy fish.

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