Oscar Fish: Facts, Care, Diet, Breeding, & More

The Oscar (Astronotus ocellatus) is a well-known freshwater fish in the fishkeeping community. This cichlid is large and aggressive with unique personality traits. They have evolved to develop beautiful coloration and patterns that make them very desirable aquarium fish. Oscars are also known by other names like tiger Oscar, velvet cichlid, and marble cichlid.

These beautiful species are easy to care for but they need a large aquarium. They are also very aggressive and with their large mouth, they can eat almost any fish that they can fit in their mouth. They are not a beginner-friendly species and you should only keep them if you already have experience keeping aggressive fish.

This care guide will teach you all you need to know about Oscar fish and how to ensure they experience a healthy and happy life with you. We’ll also provide you with tons of tips on how to take better care of your Oscar.

Species Profile & Overview

Oscar are beautiful fish originally from the tropical regions of South America. They can be found in most countries along the Amazon basin. They are often found in shallow and slow-moving waters that are slightly cloudy. This cichlid is now being commercially produced in some countries around the world for the aquarium hobby.

Oscars, like all cichlids, tend to become violent and aggressive toward other fish. This is especially true when they are in their breeding season. Because of their large size, not many fish can withstand their aggression so you should only keep them with similar-sized and aggression-level species.

Oscar fish are super smart and can recognize their owners. Some in the aquarium hobby call coscars the puppy of their tank, playful and smart. They are highly food-motivated species and will follow you around until you hand them the food.


Wild Oscar Fish In Aquarium

The wild-caught variants are often darker with fewer orange colors on them. They also come with an eye-like patch on their tail that makes other predators think twice before coming after an Oscar. The body patterns of these fish often protect them from piranha attacks.

They are also able to slightly change their coloration based on their mood. They often become more vibrant when they are protecting their territory or fighting with other fish. They also change colors and patterns throughout their lifespan. At young ages, they are often darker and have fewer colorations on them. The patterns are also very different from the adult specimens. 

They have an oval-shaped body that is quite bold and beefy. The fins are large and symmetric which gives the fish its iconic oval shape. They also have large eyes that are pooped out of their head. The eyes are often the first organ they lose in a fight. 

Since this fish is extremely popular in the hobby, many breeders have line-bred them to create different patterns and fin shapes. They are now selectively bred to develop long and flowing fins and super bright red colorations. They are now available in full Red, Orange, Yellow, Albino, and Bronze colorations as well as different patterns and fin shapes.

Oscar fish are sexually monomorphic which mean male and females look the same. Unlike other fish where it is easy to identify their gender by the shape or coloration, the male and female Oscars look the same. The best way to identify their gender is to look at their vent area. The males have a spiky vent tube and the females have a larger vent designed to lay eggs.

Adult Size

In captivity, Oscar fish can grow to about 12 – 14 inches in length and can weigh up to 1.6 kilograms. In the wild, they can even become larger and grow up to 18 inches large. 

This makes them one of the bigger types of fish you can own in a home aquarium. They will also grow at a faster rate compared to other aquarium fish. This is why we do not recommend this species for beginners. We have seen many new aquarists bring this fish home and in just a few months they realize it has already outgrown their tank. 

As mentioned, Oscar fish are fast-growing species and will become fully mature in just 12 -14 months. Many factors like genetics, diet, temperature, water quality, etc can slightly change their maturity time and size.


A healthy Oscar Fish can live up to 10 – 20 years in captivity. When water conditions and their diet is right, you can expect them to easily reach up to 20 years of age. Of course, things like genetics and external factors like diseases and infections can change this. But overall this species of aquarium fish can easily live for many many years.

If you are new to Oscar fish, we highly recommend focusing on the quality of the water to ensure your pet fish doesn’t get sick. Sicknesses can drastically lower the lifespan of any aquarium species.

Behavior and Temperament

Oscar fish are naturally aggressive hunting species. But it doesn’t mean that they will pick a fight with any fish that comes close to them. We call them gentle fighters, they are calm but will defend themselves if they find the need.

They are often calm and mind their own business when kept with similar-sized fish. Unless other species do not cause any disturbance, the Oscar fish will not show any aggression. They are such confident fighters who will only fight if someone crosses their line. 

Oscar fish, like most other cichlids, will move the substrate. So if you have rooted plants they might not be able to survive without your help. They often move the substrate in hopes of finding food but can also do it during their breeding season.

Speaking of breeding, oscars get super aggressive and territorial during the breeding season. So if you keep them in a community tank, you might want to separate them to prevent any damage to your fish. Both male and female will defend their territory with all they have!

Gold Lemon Oscar Fish
Gold Lemon Oscar

Oscar Fish Care

Oscar Fish is easy to care for but it is not a beginner-friendly fish. To keep Oscars happy, you will need to know the basics of fishkeeping plus the care requirements specifically for this species. With the right water conditions, tank setup, and diet, you can expect your pet fish to live its best life. 

In this section, we will guide you through all the information you need to provide your fish with the best possible life. 

Tank Size

Oscar Fish are large species; they need a tank that is at least 55 gallons. This is only if you want to keep a single Oscar fish and no other species is available. They get massive and need a large tank. We always recommend getting a 120-gallon tank for Oscars as you can keep more species with them. 

You might see some recommend keeping this species in smaller aquariums which is completely wrong and cruel to the animal. Yes, they will survive, but they will grow with deformities and experience a very harsh life. They will also produce a ton of waste so a large aquarium is an absolute necessity. 

If you haven’t yet got an Oscar for your aquarium, we highly recommend not purchasing this species unless you have a large aquarium. 

What To Put In An Oscar Tank

In the wild, Oscar fish live in different geological areas which makes them super hardy. They are often seen in densely planted warm areas. Recreating a similar environment will ensure the health of your fish as well as help with the aesthetic of the tank.

Like all other aquarium fish, oscars need stable water parameters that are well-oxygenated. But more importantly, you will need to pay special attention to the arrangement of the decorations in Oscar’s tank.

This fish needs open spaces to be able to freely swim and maneuver. But at the same time, they need to have a few shaded places where they can hide if under stress. You can pick your favorite rocks and driftwood to create these hiding spots. 

When picking decorations, make sure to pick natural decorations as they are much more beautiful and will give your fish a sense of being at home. At the same time, driftwood will release tannins which help with lowering the pH in your tank. Oscars prefer neutral and slightly acidic waters. More on this later in this article. 

Plants are super important to keep an aquarium clean but unfortunately, not many plants can survive with cichlids of this size. They will dig into the substrate for food and will uproot plants. So rooted fragile plants are not the ideal types of plants for an Oscar tank. 

Hard-leaf plants like anubias that do not need substrate can be a great choice. Just make sure to pick the varieties that grow large leaves. You can also add floating plants like hornwort, Dwarf water lettuce, and java moss. Some Oscars might still disturb these plants but in our experience, they live along pretty well.

To satisfy their natural digging instinct, it is best to have sand substrate in their tank. They love to dig and move the substrate around. Having sand or smaller gravels will let your fish have the tank as their playground.

Water Parameters

Oscar Fish are adapted to live in warm tropical waters so your tank should have a similar environment. The water needs to be well-oxygenated and with slow to moderate movement. Fast-moving waters will cause stress in Oscars and must be avoided. 

Below is the ideal range of water parameters you can keep Oscar Fish in: 

  • Temperature: 75 – 80 Degrees Fahrenheit 
  • PH: 6.5 – 7.8
  • TDS: 50 – 200 PPM

We keep our Oscars at 77 degrees Fahrenheit and the pH is neutral.

Wild Oscar Fish In Aquarium


Oscar fish don’t need any special lighting conditions. However, to bring out their true colorations, you can invest in a high-quality aquarium light. After all, we keep fish to enjoy their beauty! 

When lights are on you will find your fish swimming playfully in the tank. At the same time, your plants will need a strong source of light to be able to grow. A good aquarium light will make your tank more beautiful while also helping your plants to grow much better.

Most planted aquarium lights are an ideal type of light for Oscar fish. The LED planted lights are often coming with blue light which brings out the true coloration of your fish. 

Filter System

A properly maintained and healthy aquarium is critical to your Oscar fish’s long-term health. Maintaining a healthy aquarium requires a filter powerful enough to deal with the bioload it makes. Oscar fish produce a lot of waste and thus they need a strong filtration system in their tank.

Buying a good filter is like investing in the prevention of further financial losses. A good filter keeps fish healthy and prevents most diseases. This means you’ll spend less money and time in the future as your fish will stay healthy. 

A good filter should utilize both biological and mechanical filtration to clean the water for fish and human viewers. The majority of modern aquarium filters include both capabilities and will remove waste from the water more efficiently. 

Common Oscar Fish Diseases & Health Issues

Oscars are hardy but there are a few diseases that they seem to be more susceptible to. Most of these diseases are due to the negligence of their owners. These large fish need a large space to live in and the water has to be super clean at all times. 

When keeping them in smaller tanks, it is super easy for things to go wrong, especially with the amount of waste these guys produce. Oscar fish eat a lot and make a lot of waste which will pollute the water quickly. Polluted water can cause many different bacteria and ammonia-related diseases. 

Oscars are known to get “Hole in the Head” or Hexamita disease which is believed to be ammonia-related. When tank conditions are not right, they will develop a tiny hole(s) on their head which will grow and cause the fish to die.

Ich and fin rot are also common diseases that Oscar fish can contract. These external diseases can cause the fish to suffer. Both of these diseases will usually come with the new species you are adding to the tank. So it’s important to quarantine new fish for 6 – 8 weeks before adding them to your main tank. 

Diet and Feeding Requirements

These majestic fish are not picky eaters and will happily eat any food you give them. Oscars are technically omnivore species but they tend to feed more of a high-protein diet.   

In the wild, Oscar fish mainly eat insects, small fish, and the available plant matter. Similarly in captivity, you will need to provide them with a diet that has all the elements they need.

They tend to eat most commercially made dry foods without any issues. But you’ll likely need to feed them a mix of dry, frozen, and live foods. Doing this will ensure they receive all the nutrition and vitamins they need.

Cichlid pellets are great for Oscars and they will eat them like it’s a 5-star meal. Frozen foods are also great treats you can feed them a few times per week. They will happily eat most frozen fish food available in pet stores.

To make this species grow big fast, some aquarists feed them fresh Beefheart. Simply remove all the fat (100%) then ground the Beefheart and feed it to your fish a few times per week. Just make sure to do more water changes as fresh meat can pollute the tank extremely fast and might cause disease. 

That said, we do not recommend feeding Beefheart if you can’t change the water a few times per week. This superfood is only for those who want their Oscar to become a giant!

And as always, NEVER overfeed your fish! Overfeeding is the number one cause of sort of aquarium problems. This fish can live for a few days without food but overfeeding can kill it in just one day. 

Breeding Oscar Fish

Breeding Oscar Fish is a little tricky but possible. During the breeding season, they become extremely territorial so you will have to have a separate breeding tank if you want to breed them. 

It is also very hard to identify their sex to select a pair for breeding. Most people buy a group of Oscars and grow them to get a pair. When they become mature a male and a female will pair up and then it’s easy to identify the pair in the group. They will swim closely and defend a section of the tank against others.

When you see this behavior you can catch the pair and place them in their tank. You should also give them a flat surface to lay their eggs on. Oscars lay their eggs on flat horizontal surfaces so a flat stone or terracotta planter is needed so they can lay their eggs on. 

When the female is ready, she will lay about 300 – 3000 eggs. The number of eggs a female lays depends on her size and age. The bigger and older females will lay up to 3000 eggs. 

Eggs are sticky and will stay attached to the surface being laid on. The male will then fertilize the eggs and defend them until they hatch. Depending on the water conditions, eggs will hatch in about 2 – 3 days. 

You will need to hatch live brine shrimps and feed them to your Oscar fry a few times per day. The fry will grow quickly and will soon need a bigger tank.

Tank Mates

Oscars are large aggressive species so they need to live with similar fish. We prefer to keep them in an Oscar-only tank, but there are a lot of fish that can live with them. They will eat any small species that can fit in their mouth so make sure all your fish are around the same size even if they are compatible with Oscar.

Even if all the fish species are similar-sized and semi-aggressive, you will still need to monitor your tank regularly to make sure they are not picking on each other. This is especially true for the first few days you are adding any new fish to your tank. 

Oscars also have personalities and some are more aggressive than others. Even if we mention a species is compatible with Oscars it doesn’t mean your pet Oscar will live peacefully with other fish.

Considering all of these points, here are our top tank mates for your Oscar fish:

Gold Lemon Oscar Fish
Gold Lemon Oscar Fish


Oscar fish are easy to care for species but will need their own basic care requirements to thrive. They are super smart species and will bond with their owners. They can be great pets if you provide them with a large tank and the right tank setup. 

They are not beginner-friendly species so you need to have some experience with South American cichlids before deciding to own an Oscar. With the help of this article and your past experiences, you can easily keep this fish and enjoy watching it grow. 

We have covered some of the most common questions about Oscar species in another article; you can find them here: Commonly Asked Oscar Fish Questions

Astronotus ocellatus
Sexual shape dimorphism in the monomorphic fish Decapterus macrosoma (Teleostei: Carangidae)
Astronotus Arowana