The Oscars are one of the most popular species of fish for freshwater aquariums. They are often included in larger starter aquariums, and are known for being quite active. They are a type of cichlid fish, originating from South America. They are known to be aggressive with each other and other fish species.

Because of their aggressive nature the Oscar is usually the first fish for the aquarium. We suggest that you pick its tank mates carefully to avoid having your entire aquarium eaten by the Oscar. This is why it’s generally a bad idea to introduce this fish to an existing aquarium as an afterthought.

They are nocturnal, which means they spend the day sleeping in a sheltered spot, and come out at night to hunt for food. For a family aquarium this could be a bit of a problem, but generally they will be alerted at feeding time by the splashing and movement of other fish in the tank

Even after all of the warnings, many families cannot resist buying an Oscar because their coloring makes them a very attractive addition to almost any tank.


Information on Oscars

  • Average Length: 10 – 12 inches
  • Scale Colors: Black, Orange, Red or Lemon (with or without markings)
  • Attention Needs: High
  • Good tolerance to Heat and Cold: Yes
  • Good Pet: Yes!
  • Good with Other Oscar: Yes
  • Good with Other fish species: No, they are aggressive
  • Suitable for First-Time fish Owners: No
  • Health Concerns: They tend to have Septicemia, Fin Rot, Head in the Hole and White Spot Disease.
  • Average Life Span: 10 to 15 years

Physical Appearance of Oscars

Oscars have a long and oval-shaped body. They have long and extended dorsal and anal fins that stretch along the body towards the caudal fin. 

Oscars are known to get very long when they are fully grown. Baby Oscars may only measure between 1 to 2 inches but can grow very fast. They can grow an inch every month and may reach up to 10 or 12 inches when they are fully grown. 

The most commonly found Oscars have irregular markings of black and orange, which are called tiger Oscars. Years of selective breeding have also resulted in many different color variations.

Lemon and red Oscars are other common types. Some Oscars can also have completely solid color bodies with black or white markings on the fins. These markings often have an eye-spot appearance which is called ocelli. Oscars can also come in the albino type, having an all white-colored body with red spots.

The spots or ocelli act as a defense mechanism for Oscars as it confuses the predators. Predators think it is an eye, which makes it difficult for them to understand which way the fish will swim.

Baby Oscars and fully-matured Oscars also tend to have a slightly different appearance. Baby Oscars have striped bands of orange or white on their body while adults do not.

An interesting feature of their appearance is that Oscars can change colors. There can be several reasons for this which will be covered at the end of this article under related questions.

Temperament of Oscars

Oscars belong to the Cichlid family of fish species which are generally known to be aggressive. Oscars are naturally territorial and can get aggressive towards other fish in the tank. They have been known to attack other fish, especially when the Oscars are mating or feeding. 

They get along with other Oscars and like to stay in pairs or small groups. It is recommended to keep them in pairs, or as many as 5 together. Avoid keeping three as that may result in two bonding well and one being left alone

They spend most of their time in the middle to top level of the aquarium but may head to the bottom of the tank to look for food. 

Oscars are active and are known to uproot the plants and other decorations in the tank. So all the decorations should be tightly attached to keep the Oscars from damaging them.

Oscars are one of the most intelligent fish species. They seem to sense the surroundings outside the tank and are often found to interact with their owners. The Oscars will waggle their tails, fins and heads when they see you approaching the tank. Because of this behavior they are often called “water dogs”.


Best Habitat for Oscars

A tank of around 55 gallons is the minimum size to consider for this fish. If you are able to go with a 75 gallon or larger tank it will be better for the health of the fish. Water conditions that closely resemble their natural tropical conditions will help keep the Oscars healthy. They are found in slightly warm and slightly acidic to slightly alkaline water.

Tank size

3 to 5 baby Oscar fish can easily be kept in a small tank of 30 gallons but a fully matured Oscar will need a minimum tank size of 55 gallons. For every additional adult Oscar, they will need another 20 gallons. A community fish tank will need to be even larger.



They need a water temperature between 75°F to 80°F.

Water Hardness and pH

Oscars need water that is mildly acidic to slightly alkaline, so the pH should be in the range of 6 to 7.5. The water hardness should be between 12 to 15 dH.

Tank Substrate

Oscars are scavengers and like to dig for food, so a soft substrate like sand should be used inside the tank. Avoid using a rough substrate like gravel as it can hurt them when they are digging.


They don’t have any specific lighting needs so any type of regular aquarium lighting will do. Because other fish will usually need a typical daylight cycle it is suggested that you use a timer to control the lighting in the tank.


Decorations like plants, rocks and driftwood help replicate their natural environment. Caves can also be added to create hiding places for the Oscars. Keep in mind that these fish can grow very large, up to 12 inches so the size of the decorations like rocks and caves should be added with their full size in mind. This will prevent you from the hassle of changing the decorations in the future once they have fully grown. 

An important thing to keep in mind when adding decorations is to firmly attach all of them to the substrate. If you do not do this there is a good chance that Oscars will uproot them. Along with the decorations, air pumps, water filters or any other tank equipment should be attached as well as possible. Oscars are known to damage things if they are not properly secured.

Tank conditions

Oscars can generate a lot of waste and it is important to add a high-quality filtration system that can efficiently clean the waste. A Canister filter is recommended as they are easy to use and also efficient at keeping the water clean.

Tank Maintenance 

The tank temperature, alkalinity, pH and level of dissolved organic compounds should be measured daily. Oscars are large and tend to generate a lot more waste than smaller fish. 

To keep the level of waste and toxic compounds under control, a water change of 20 to 30% should be performed every other week.

Best Tank Mates for Oscars

There are several things that you need to consider before getting a tank mate for the Oscars. These fish are large and tend to be aggressive. So avoid keeping smaller fish with the Oscars because they will chase or eat the smaller fish. We recommend adding fish that are about the same size or large enough not to be eaten by the Oscars. The fish that you add should also be active and ready to compete for food, otherwise Oscars may chase them away.

Another important thing to look into is the size of the tank. Since both the Oscars and their tank mates are going to be large, a very large tank will be needed. This will make sure all the fish in the tank have enough space for themselves and lessen the chances of fighting between them. 


Best tank mates include:

  • Silver Arowanas
  • Blood Parrots
  • Sailfin or Common Plecos
  • Clown Loaches
  • Bichirs
  • Severum
  • Convict Cichlids
  • Silver Dollars
  • Jack Dempsey
  • Giant Gourami

Avoid adding snails and shrimp. Just like the smaller fish species, Oscars will just eat them.


Health Issues

These fish are hardy and generally do not get sick very often. Still they have been known to have the following diseases:

Hole in the Head

This is a common disease that is known to affect freshwater cichlids like Oscars. The disease results in cavity-like formations on the head and other parts of the body. Symptoms include stringy and white feces and faded coloring on their body. Infected fish sometimes also tend to lose their appetite and become thin. The hole in the head disease is generally caused by nutritional deficiencies and is easy to treat if detected early on. The best way to prevent your Oscars from getting the disease is to feed them a well-balanced diet.

Fin Rot

Fin Rot or Tail Rot is a common disease in freshwater fish. The disease results in the fins or the tails of the fish developing a white coloring or becoming tattered. In advanced stages the disease can also lead to the development of bloody patches near the fins. Fin Rot is caused by a fungal or bacterial infection which is a result of poor water conditions. 

To prevent the spread of the disease, infected fish should be quarantined in a separate tank. The disease is generally treated using antibiotics. Consult your vet if you think your fish have this disease.


An open wound or injury on your fish that is left untreated can often result in a bacterial disease called Septicemia. The disease is highly contagious and fatal. Infected fish can have hemorrhages on the eyes, gills, body or at the base of the fins. It can also result in swollen abdomens, dark coloration or the eyes of the fish popping out. Sometimes infected fish will also swim abnormally. 

One serious concern about Septicemia disease is that some infected fish may show no signs of the disease, yet they can potentially spread it to others in the tank. 

If you notice any changes in the behavior or appearance of your fish it is always a good idea to consult your vet.

Ich or White Spot Disease

Ich is a common disease that can infect both freshwater and saltwater fish species. The disease is caused by a parasite that is capable of reproducing and multiplying rapidly. The most common way for the disease to enter your tank is while adding new plants, or fish and when giving Oscars live food. As a preventive measure you can quarantine new plants and fish in a separate tank before adding them to your Oscar fish tank. 


Symptoms of the disease include:

  • White spots on skin and gills
  • Reddening of fins
  • Loss of appetite
  • Sitting at the bottom of the tank
  • Rubbing the body against the tank

There are several ways to treat the disease, the most common being adding salt to the tank. It is recommended to treat infected fish in a separate treatment tank and then treat them. Another easy solution is to slightly increase the water temperature of the tank. Some antibiotic medications can also be used to treat White Spot Disease. If you find any signs of the disease in your Oscars, consult with your vet.

fish flakes

Feeding Oscars

Oscars are omnivores who feed on a variety of small insects, fish, crustaceans and small amounts of plant debris in their natural environment.

Captive raised Oscars can be fed commercial fish foods like pellets or flakes. These foods will provide most of the nutrients that the fish needs. They can also be given frozen or live food like bloodworms, brine shrimp and daphnia (a type of small crustacean). Whenever possible try to give them live food. This will help them use some of their natural aggression as part of normal hunting behavior. 

They also need fiber in their diet which can be given by feeding them finely chopped kitchen vegetables or algae flakes.

Oscars should be fed 2 to 3 times a day and only what they can finish within a few minutes. Make sure to feed them enough food. If they are not fed enough Oscars will get aggressive competing with each other when they are feeding.

Related Questions:

Why do Oscars change colors?

Baby Oscars are born with a somewhat dull coloration. As they grow, the coloration on their body becomes bright. This is one reason for them to change colors and is a gradual and long process. They are also known to change colors depending on their mood. It is difficult to pinpoint the exact color that different moods can cause. Oscars tend to get brighter in color when they get aggressive or upset. Sometimes the color change can also be caused by poor water conditions or a disease like Ich or White Spot.

Are Oscars difficult to keep for new fish tank owners?

As already discussed, Oscars can get very large and are also aggressive fish. This makes it difficult for new fish tank owners to care for them. Selecting and keeping tank mates for them is also not easy. Oscars need a large tank which makes it difficult for new fish tank owners to maintain the best water conditions. Oscars along with their tank mates will generate a lot of waste. This will require frequent and larger water changes than what is generally required for tanks with smaller fish. Oscars are only recommended for owners that can spend the time to make sure the water quality is maintained.

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