What Do Fish Do All Day In Your Aquarium?

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You come home from work or school, fix yourself something to eat, and sit down to relax for the evening. All the while, your fishy friends follow your every move, watching you from behind the viewing panes of their fish tank. 

So, you feed your fish. Maybe you sit and observe your pets’ behavior as they gobble up their food. But did you ever wonder what your fish get up to all day while you’re not around? And what do they do all night when you’re asleep in bed?

Let’s find out!

Diurnal vs. Nocturnal Fish

What individual fish do depends mainly on the species and on whether the fish are diurnal or nocturnal.

Most species of aquarium fish are diurnal, which means they’re most active during the daytime. Nocturnal fish, on the other hand, are mainly active at night. There are also crepuscular fish species that are primarily active around dusk and dawn. Some species of fish can adapt to hunt or become more active at other times of the day, whereas others remain constant.

Interestingly, most predatory fish tend to be nocturnal, hunting under the cover of darkness, whereas herbivores and omnivores are primarily active during the daytime.

The Importance Of The Day/Night Cycle

When the sun rises in the morning, you wake up after a refreshing night’s sleep to start your day. At night, when it gets dark, you go to bed to rest and recharge your body after a busy day. Well, your fish are just the same! 

In nature, when it gets light in the morning, crepuscular fish emerge from their overnight shelter. Diurnal fish become active, too. Your fishes’ first instinct is to feed. In nature, it’s the same. Insects also become active when daylight arrives, settling on the water surface and providing food for fish, such as bettas. 

In contrast, nocturnal fish species head for cover where they can safely spend the daylight hours.

Later in the day, around dusk, crepuscular creatures get busy feeding again before they settle down for the night. Daytime fishes begin to wind down, and when the sun sets and darkness falls, diurnal fish become inactive and find a safe hiding place to spend the night. 

Once it’s dark, the night shift arrives. Nocturnal fish emerge from their sleeping quarters and begin their nighttime hunt for food.

In The Aquarium

Fish In Aquarium

So, your fish live in the controlled environment of your aquarium, but that doesn’t mean that the day-night cycle is any less important to them.

Without light and darkness, your fish don’t know when it’s time to feed and to rest. That’s extremely stressful to the fish, potentially leading to a compromised immune system, making your fish vulnerable to attack by parasites, bacteria, and other common fish diseases.

These days, you can buy aquarium lighting solutions with integral timers, enabling you to set the lights to come on and go off as required. That way, even if you’re not around to turn the lights on and off manually, your fish will still enjoy the natural day/night light cycle. 

Alternatively, if you can’t afford to upgrade your lighting unit, you can buy a timer from your local hardware or DIY store. Timers are inexpensive, simple devices that allow you to preset the times you want your tank lights to turn on and off. Simply plug your lighting unit into the timer, plug the timer into the main power outlet, and you’re good to go.

Nocturnal Fish Behavior

So, you now know that nocturnal fish do their fishy business at night while you’re asleep. Nocturnal species of aquarium fish include most freshwater eels and knifefish.

But how do nocturnal fish manage to live and feed in the pitch black?

Well, some adaptations enable nocturnal fish to survive in their dark environment:

  • Nocturnal fish generally swim more slowly than diurnal fish simply because of the reduced visibility.
  • Night-time fish tend to have large eyes to maximize the light that’s available to them.
  • Nocturnal fish are typically solitary types that are less likely to swim in schools.
  • During the daytime, when the tank lights are on, nocturnal fish usually hide away until it’s dark again.
  • Night-dwellers are generally drab in color, typically yellow-brown or red, so they are camouflaged in low light conditions.
  • Nocturnal fish often have a very well-developed lateral line that helps them sense water movement more efficiently and effectively.

If you have nocturnal fish, you can observe what they get up to by investing in a moonlighting effect light system that you can use during the early evening before you go to bed. Moonlighting fools the fish into believing that night has fallen, so they become active, enabling you to watch their behavior.

You should also feed nocturnal species right before lights out, as that’s when the fish are naturally programmed to hunt for food. That way, you get to watch your fish doing what comes naturally.

When the sun comes up, nocturnal fish sleep or lie up in the shelter of a cave, dense plants, or underneath driftwood, digesting their food and recharging their batteries before it’s time to come out again when darkness falls.

Diurnal Fish Behavior

Fish that are active during the daytime usually begin by feeding. That might involve scavenging around the tank bottom for scraps of food, eating whatever flakes or pellets you scatter on the water surface, or grazing on the colonies of algae that grow on tank surfaces. Depending on the species, foraging for food can take up most of the fish’s day.

Territorial fish, such as bettas, will spend part of the day patrolling their patch. In the wild environment, a betta will chase off any potential intruders. Schooling fish swim together in a shoal, exploring their environment and seeking safety in their group. Sociable fish, such as goldfish and Corydoras catfish, seem to enjoy just hanging out together, looking for food, or just swimming around the tank.

As you will know if you keep them, many tropical fish species, especially livebearers such as guppies and platys, spend a large amount of their time spawning. Egg-laying fish can be prolific spawners, too, depending on the species. Since many of the fry and eggs are eaten by the parents or by other fish in the community, reproduction is an almost constant activity, presumably to replace the young lost to predation.

Older fish and species such as bettas enjoy “napping” when they rest on a flat leaf, in a cave, or simply on the substrate between periods of activity.

In Conclusion

Now you know what your fishy friends get up to during the day while you’re out at work and overnight when you’re fast asleep in bed.

To replicate the fishes’ natural behavior and keep stress at bay, be sure to have your tank lights on during the daytime and off at night.

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