FIA is community supported website. When you purchase through links on our site, we may earn an affiliate commission. Learn More.

Oscar Fish: Overview, Tank Setup, Diet, Care & More

Oscar Fish are known for their territorial behavior and are prone to aggression when placed close to other fish.

At first glance, they appear to be rather peaceful because of their graceful swimming patterns, but that isn’t the case.

Most aquarists are attracted to the Oscar fish because of their vivid colors and active presence in the tank, but will also appreciate their higher-than-average intelligence and complicated social behavior.

Species Overview

Level of CareMedium to Difficult
TemperamentTerritorial and Aggressive
AppearanceVaried Appearance
Life ExpectancyLive for over 20 years
Size1 foot and above
DietMeat and vegetables
Tank Size50+ gallons
Tank EnvironmentFreshwater with caves and rocks
Tank MatesLarge peaceful fish

Native to the Brazilian, Columbian, and Peru waters, they can be found in the Amazon river and the surrounding waters.

Their population is also scattered across China and North America, but this could be attributed to the fish industry. Their Latin name is Astronotus oscellatus, and they belong to the Cichlidae family.

They will live for over 20 years and grow up to a size of around 12 inches long.

As most fishkeepers will quickly find out, they are not very friendly, which is why they should only be looked after by experienced aquarists.

They are easy to feed because of their omnivorous diet and will eat just about anything, but you will have difficulty finding suitable tank mates.

The Oscars are worthy of a place in your tank, and their complex behavior will have you on the hook for several hours on end.

In this guide, we’ll learn all there is to know about the Oscar, including tank mates, breeding guide, ideal tank setups, and much more.


One of the most beautiful freshwater fish you can find, with various markings of red, yellow, and orange on the sides.

The majority that grows in the wild often have dark brown and green blotches. Lemon and Red Oscar have bodies that have a solid color, which may change over time.

The most popular variant of the Oscars is the albinos, who have bold white markings all over their bodies.

Their fins are mostly black, and their eyes have an orange are an orange rim that slightly protrudes above the head.

They will grow up to at least 12 inches in both the Aquarium and the wild and weigh in at around 1.5 kg. The fish industry is known for creating new varieties through selective breeding.


Oscar fish can grow to a length of between 12 inches and 18 inches long. When fully mature, they reach a weight of up to 3 pounds. In aquariums, they will reach only about 12 inches, but larger sizes have been reported.


In the wild, Oscar fish can live for about 20 years. However, if you provide them with the correct aquarium conditions, care, and diet, they can live for more than 15 years, give or take.

Behavior & Temperament

They are intensely territorial, so make sure to take this into account before adding them to your tank.

They are incredibly likely to hunt their tank mates and will do so with the intent to kill if another fish gets too close or seems to encroach onto their territory.

Their levels of aggression get even higher when it’s feeding time and mating, which can fuel a lot of that territorial behavior.

They will spend most of their time swimming in the mid-section of the aquarium, although they’ll often swim down to the bottom of the tank to get something to eat.

They have incredibly destructive tendencies and will uproot decorations and plants while searching for food, which means that everything in the tank must be secured appropriately.

Once you manage to set up the tank correctly and pair them with the right fish, you can somewhat control their temperament.

Tank Setup

They originate from the fast-moving South American freshwaters with their neutral pH values.

Their bodies will not tolerate anything too acidic or alkaline. Make sure your water tank can provide high water flows to mimic the conditions found in Amazonian rivers. It should be reasonably easy to do.

Create a layer of a soft substrate at the Aquarium’s base. The substrate should be incredibly soft, so the sand would be an excellent place to start.

They are known to dig underneath the substrate, and anything, too course, could hurt their bodies.

When it comes to decorations, you have got a lot of choices in the matter. However, if you’re going for that all-natural look, consider adding only bogwood and rocks around the tank.

Either way, make sure to secure the decorations in their spots firmly; otherwise, the Oscars will uproot and destroy them.

Before selecting plants, make sure to choose hardy species that can withstand the trauma of being around the aggressive Oscars. A good candidate would be the hornwort.

While these are unlikely to eat live plants, they will hurt them while digging into the substrate.

Tank Conditions

  • They quickly reach over 12 inches in size and will need a pretty big tank to live. Anything less than 50 gallons would be too small, contributing to elevated stress levels and fueling their aggression. Add 20 to 30 gallons more for each additional fish.
  • The water should be extremely neutral between 6 to 8 pH at 75-80° Fahrenheit.
  • There’s a lot of sunlight in Oscar’s natural habitat, so make sure to install a few artificial lighting too.
  • Ensure a heater if you live in colder climates where temperatures are known to drop below 70° Fahrenheit.

Other than that, you don’t need special apparatus to regulate the water, just a regular filter for cleaning.

Just make sure to attach the equipment firmly, or they will get dislodged out of the area because your Oscar may attack it.

Having an adventurous temperament, they will try to jump out of the tank, so make sure to attach a very firm lid to the tank.

These are relatively big fish at 1.5 kg and will easily knock out the roof if it isn’t securely attached.

Oscar fish front facing

Tank Mates

As mentioned above, Oscar is not looking to make any friends. Their aggression will cause other fish to live under extreme stress.

That being said, their natural habitats are incredibly diverse, so they can get along with others if their tank is large enough. For the most part, you should only keep them in your tank if you don’t want them to turn aggressive.

However, if you want to add mates, only choose large and peaceful fish that can defend themselves when the going gets tough (and it will).

Ideal tank mates include red terrors, sailfin plecos and jack dempseys, both of which are sizeable communal fish. Smaller fish will not survive long.

Food & Diet

It is relatively easy to provide a healthy diet to Oscars because they are omnivorous and will eat just about anything.

In their natural habitat, They would thrive on smaller fish, plant debris, and insects.

Their primary diet always consists of lots of meat and proteins, with vegetables thrown in the mix for some variety. You can also provide them with pellet foods and flakes from a pet store.

While most flakes are designed to provide a well-balanced diet to them, you can buy those made explicitly for Oscars.

Other food choices include live and frozen foods, including brine shrimp, daphnia, and bloodworms. Live foods will quickly bring out the instincts of your Oscars.

If you have spare vegetables leftover, you can try chopping them up and feeding Them.

They might eat a few, but this won’t become the central part of their diet provided if they’re getting all their nutrition.

It would help if you fed them 2 to 3 times every day, in amounts they can finish in 3 to 4 minutes. Other Oscars are known for getting violent when it’s feeding time, so watch out.

Oscar Fish Care

Oscars are not ideal for beginners because they require a lot of care. They have a reasonably large appetite and grow very big, which means they will make a lot of mess on a semi-regular basis. It means their tank needs to be cleaned every once a week.

Although these are relatively more resistant than other fish to diseases, they are prone to getting sick. One common disease is lateral line erosion, which causes holes and cavities to form on their bodies.

The best way to treat this disease is to change their diet and provide them with more nutrients.

Live food can cause your Oscar to fall ill since they often harbor bacteria. It makes it essential to quarantine feeder fish before introducing them to your Oscar’s diet if you want to prevent them from getting sick.

Avoid overfeeding because this could lead to various issues, including constipation.

Their primary diet consists of dried food which is a problem for fish as they could contribute to bloat and blockage that could ultimately result in their death.

The best way to counter this problem is to buy dry foods containing probiotics to minimize the risk of bloat, blockage, and constipation.

Alternatively, you can use supplement foods that contain a high level of moisture content.

2 oscar fish in aquarium

Breeding Guidelines

Oscars are monomorphic species, which means that both sexes have the same appearance. It also makes it harder to breed them.

You will have to take a closer look at their genitals to identify them correctly. And even then, it can be extremely tough to breed them because Oscars are incredibly picky when choosing a mate.

Some fishkeepers often buy breeding pairs. Alternatively, you can buy them young.

The idea is that as they grow together, they will build some form of connection and will eventually form pairs.

The only problem is that these will take around two years to reach maturity. It is an effective way to breed different varieties and colors of Oscars.

In their natural environment, these Cichlids would breed at the peak of the rain season.

You can mimic these conditions by decreasing the temperature of the tank by a few°, changing the water every few days, and sprinkling some water on the surface for added effect.

Oscars will indicate that they’re ready to mate by flaring their gills and fins. It will create vibrations in the tank.

Before breeding, the pair would find a suitable place to lay their eggs. They’ll clean a few rocks to lay eggs. Some females are known for producing over 3000 eggs.

Oscars are known for defending their eggs until they hatch (which only takes a few days). Males will guard the eggs and stay close by, while females will fan the eggs to prevent the silt and sediments from smothering them.

Eggs Hatching

Oscar eggs will hatch within 2 to 3 days of being laid. It is common to find that all of the eggs have disappeared from the tank,

It is because they haven’t been fertilized, and the parents have eaten them. Oscars may also consume their eggs if they feel unsafe or become upset for any reason.

In some cases, it could take a little while before a pair become parents.

Unfertilized eggs can develop a type of fungus that could spread to fertilized eggs. You can remove the fungus by adding Methylene blue to the tank.

Fertilized Oscar eggs will have a tan or light brown color as opposed to the white unfertilized eggs.

It is not uncommon for the fry to get eaten by its parent, which means you may have to intervene and provide the fry with another place to call home. It will increase their chances of survival.

Make sure to move the eggs to another tank before they start hatching. Expect the parents to get violent as they attempt to defend their eggs as you try to remove them.

When transporting the eggs to a new tank, place them into a container to prevent the eggs from getting exposed to air. Now you’ll have to wait and watch.

Note: Borrow some of the water from the old tank into the new tank. An Oscar fry will not survive in poor water conditions.

In the wild, the parents will oxygenate their eggs, but you can do the same with an air stone. Place the air stone next to the egg.

The air stone will create bubbles that flow across to the eggs. These bubbles will play the same role as the mother fanning her eggs with her pectoral fins.

When the eggs are about to hatch, you’ll notice the fry visibly moving within their eggs.

For the first few days, the fry will have an egg sack that will provide it with nutrition, so you won’t have to feed it. Once the egg sag is fully consumed, it’s time for you to intervene.

Provide the fry insofar before graduating up to baby brine shrimp in a week.

Make sure to feed the fry every three days, and remove any excess food and waste in the tank. An Oscar fry will stay by its parent’s side in the wild until it’s about 1 inch long.

In the tank, the parents could quickly become too aggressive and territorial to let the fry reach adulthood.

When the fry is around 2 inches long, you could sell it to pet stores.

It is common for eggs not to hatch at all. If this problem persists, they may be infertile. In this case, find a new pair and start afresh.

Where to Buy?

It is easy to buy these from a pet store near you. However, if you want to buy a pair, you may have to get a little creative.

Fishkeepers will often have a pair of Oscar fish for sale on online stores and forums so that you can try there.

Make sure your Oscars are healthy before buying them. Make sure their appearance matches the description of the species you want to buy.

Some Oscars share the same traits, making it slightly difficult to identify them in stores. Getting this right is essential because each species may have its requirements for an aquarium.

Final Thoughts

Oscars are territorial fish that will quickly make life difficult for other fish in your tank. They can be cruel (and deadly) to their fry and smaller fish. As a general rule, if it can fish in your Oscar’s mouth, it won’t have very long to live. Breeding is next to impossible if a pair hasn’t already been established before buying them.

But other than that, caring for them is relatively easy. But if you care about breeding, it’s best to look elsewhere. Because of their long life span, you will quickly become attached to your Oscar fish.