Oscar Fish Care: Size, Food, Tank Size & Hole in the Head

Common Name(s)Oscar Fish, Tiger Oscar, Oscar Cichlid, Velvet Cichlid, Mabled Cichlid, Water Dog
Scientific NameAstronotus ocellatus
OriginSouth America
Temperature74-80 °F
Size8-16 inches
Minimum Tank Size50 gallons
FoodOmnivorous diet (pellet food, freeze dried shrimp, live worms, peas, etc.)
Lifespan20 years
Water pH6.0-8.0
Tank MatesPotential tank mates include Firemouth, Jack dempsey, Common pleco and Clown loaches.
BreedingBreeding pair spawn eggs
DiseaseMay be susceptible to Hole in the Head disease.

Oscar Fish Facts

  • Oscar fish have lots of character
  • During their first year, they can grow 1 inch per month
  • They are one of the most mistreated fish
Oscar Fish, Astronotus ocellatus
Oscar Fish (Astronotus ocellatus)

Oscar Fish Care

Oscar fish are more intelligent than your average aquarium fish. They are very personable fish that will interact with the owner. For example, when they are excited about their favorite food, they might wag their tail fin, just like a puppy. This is why they are nicknamed “Water Dogs.” Since they have so much personality, many fishkeepers become very attached to them.

They are attractive fish with a striking appearance. They are available in many local fish stores as small juvenile fish with large eyes. Unfortunately, many people purchase these fish without understanding that they grow to a very large size very quickly. This is one of the reasons why oscars are often crammed into small tanks that are unsuitable for them.

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Oscar Fish Tank Setup & Tank Size

Oscars are generally hardy fish, but they have certain requirements for a fish tank that must be met. Since a full grown oscar can reach 12 inches or more, tank size is an important factor to consider.

Tank Size

For a full grown oscar, a minimum tank size of 55 gallon is required. However, a 75 gallon tank or larger tank is recommended. If you wish to keep multiple oscars in one tank, you should add a minimum of 20-30 gallons to the tank size per fish. If you wish to house multiple full grown oscars, a 125 gallon tank or larger would be ideal.

Aquarium tank size can become an issue for oscar fish since they grow to a large size very quickly. They are often sold as small juvenile fish ranging from 1-3 inches. However, these fish grow much faster than many people expect them to. Since oscars can grow up to an inch per month during their first year, it will outgrow a small tank very quickly. Many new owners are not aware of this, and they are not prepared to house a fish that is close to a foot in length.  

In addition to the volume of the fish tank, the shape of the tank should be considered as well. If it is a narrow tank, the fish could have trouble turning around at the end of the tank. Keep in mind that a full grown oscar fish can be 12 inches or more in length. The tank should allow the fish to turn around without bumping into the walls of the aquarium.

Filtration System

A good aquarium filtration system, such as canister filters, are required for oscar fish. Keep in mind that oscars are large in terms of girth and weight, not only length. This means that these fish have a large bio load. They consume a lot of food and produce lots of waste.


Oscar fish prefer moderate to low aquarium lighting. Lighting should be set on a daily cycle to mimic the natural day and night cycle. 8-12 hours of light is sufficient. Standard aquarium lighting will be sufficient. LED lighting will help display the oscars’ colors very well.


Decorating an oscar tank can be a challenge. Oscars are large fish and they will be strong enough to move small objects and uproot plants in an aquarium. In general, most oscar tanks are decorated very minimally. A large rock or driftwood can be placed in tanks as a centerpiece. Natural decorations can mimic the looks of oscars’ wild habitat and environment in the Amazon basin. Keep in mind that too much decoration can take away from the oscars’ swimming space.

Oscar Fish pH

  • Acceptable pH Level: 6.0-8.0
  • Optimal pH Level: 6.8-7.2

In regards to the water parameters, oscars are generally hardy fish. Most oscars have been bred in captivity for many generations, so they are able to live within a pH level of 6.5-8. However, optimal pH range is 6.8-7.2. If you wish to breed oscars, the pH level should be in this optimal range.

Oscar Fish Temperature

  • Acceptable Temperature: 74-80 °F
  • Optimal Temperature: 76-78 °F

Oscars can live in a temperature range of 74-80 °F. Since oscars tropical fish from the Amazon river, the optimal temperatures are 76-78 °F. If the temperature is too low, oscars can be more susceptible to infection and disease. If the temperature is too high, oxygen levels in the water can become depleted. A reliable aquarium heater, and an aquarium thermometer is important.

Oscar Fish Food

What Food do Oscar Fish Eat in the Wild?

Oscar fish are omnivores. They originate in rivers and pools of water in the Amazon basin. They are opportunistic feeders that will eat a variety of food which includes insects, crustaceans, and other invertebrates. They may also feed on vegetation, fruits, and seeds.

Oscars will also eat other fish. They are able to swim quickly for short distances, allowing them to hunt other fish occasionally. However, oscars are not true piscivores. Therefore, their diet may consist of other fish, but this is not their main source of food.

What Oscar Fish Eat in the Wild #Shorts

Best Food for Oscar Fish

Feeding a quality cichlid or oscar pellet food is a great way to meet the oscars’ daily nutritional needs.

In addition, pellet food can be supplemented with many other food such as freeze dried food, fresh food, and live food. Here’s a list of some of the best food that can be fed to oscars:

  • Freeze dried shrimp
  • Fresh shrimp
  • Fresh scallops
  • Fresh clams
  • Live snails
  • Live earthworms
  • Live mealworms
  • Peas
  • Bananas

Best Food for Oscar Fish Growth

The best food for growing oscar fish is a high protein diet. While oscars are omnivores, juvenile oscars that are growing rapidly need protein in their diet. In addition to high protein flake and pellet fish food, their diet should be supplemented with fresh and live fish food. White worms are great for juvenile oscars. They are known for the high protein and fat content, which is vital for growth.

Growth rate is affected by the feed patterns as well. Rather than feeding one large meal a day, juvenile oscars should be fed 2-3 times a day. Feeding different types of food each time is a good way to vary their diet.

Once the juveniles reach 4-6 inches in length, the frequency of the feedings can be changed to 1-2 times a day. The oscars should be more established and feeding should become easier.

At 7-8 inches, oscars are considred adults. While they are still growing, it is important to watch the weight of the oscar. If the oscar is gaining too much fat, the feed type and/or frequency should be adjusted accordingly. Adult oscars can be once a day or every other day.

Oscar Fish Feeding #shorts

Oscar Fish Size

Oscar fish are often sold as 1-3 inch juvenile fish, but they will quickly grow within the first year. They can grow up to an inch per year, reaching almost a foot in length. Full grown oscars in captivity are usually 11-12 inches in length. However, some oscars will grow up to 16 inches and weight well over 3 lbs.

Oscar Fish Behavior

Oscars are intelligent fish that will interact with their owner constantly. This is the reason why they are often nicknamed “water dog.” They will come up to the front of the tank when they see their owner. They may wag their tail fin and beg for food, which almost mimics a puppy. They can be moody as well. If they dislike what is going on in the tank, a water change for example, they may sulk and recede to the corner of the tank.

They are very curious fish. The will turn rocks and other decorations in the tank if they can. Many plants will most likely be uprooted.

Oscar Fish Tank Mates

Not all fish are compatible fish oscars. Oscars, like many cichlids, can be territorial. As they often do in their natural habitat, an oscar may try to protect their territory against other fish in an aquarium. In addition, they may eat other fish if they are small enough.

While oscars may show mild aggression towards other fish, they are susceptible to bullying themselves. If an oscar is placed with other large aggressive fish, they can be vulnerable to their attacks.

Here’s a list of some possible tank mates for oscars:

  • Firemouth
  • Jack dempsey
  • Common pleco
  • Arowana
  • Clown loaches
  • Freshwater Stingrays
  • Giant gouramis

Keep in mind that there is always a chance that these fish can become aggressive towards each other. Especially when the fish are initially introduced into the same aquarium, extra caution should be taken.

Many of these fish are large fish. If you intend to add these fish to an oscar tank, make sure there is enough space for all fish. Make sure the filtration system is able to handle the bio load for all of the fish as well.

Oscar Fish Types

Tiger oscar, red oscar, and albino oscar are the three main types of oscar fish. However, these are many more varieties of oscars today. Here’s a list of some of the oscar fish known today:

  • Tiger oscar
  • Black tiger oscar
  • Blue tiger oscar
  • White tiger oscar
  • Copper oscar
  • Golden oscar
  • White oscar
  • Red oscar
  • Albino oscar
  • Lutino oscar
  • Lemon oscar
  • Blue oscar
  • Veiltail oscar
  • Short body oscar

Oscar Fish Diseases

Oscars are known to get bacteria and parasite infections. One common disease in ocscars are hole in the head.

Hole in the Head Disease

Hole in the Head is a common disease in freshwater fish such as cichlids, and oscars are susceptible to it as well. Hole in the Head is also known as Freshwater Head and Lateral Line Erosion (FHLLE).

Some signs and symptoms of hole in the head disease include:

  • lesions in the head
  • loss of appetite
  • lethargy
  • white sores around eyes

If the fish is left untreated, the small legions may become increase in size and become infected. If left untreated, the fish will start to lose its appetite and eventually die.

If signs of hole in the head disease is detected, it is important to act quickly.

Possible Causes of Hole in the Head Disease for Oscar Fish

Poor water quality
Nitrite, nitrate, ammonia, pH levels may be out of the desirable parameters.

Poor nutrition
Mineral and vitamin deficiencies.

Hexamita, a flagellate parasite, can affects the abdominal cavity, gall bladder, spleen, and kidneys of the fish.

Stress can be caused by many factors such as poor water quality and oxygen deficiency. Overcrowded tank can also be a cause of stress. Drastic temperature fluctuations during water changes or malfunctioning heaters.

Weak Immune System
Fish with weak immune system, such as older fish, are more susceptible to hole in the head disease.

Treatment for Hole in the Head Disease

Since poor water quality is a major cause of hole in the head disease, it is a good idea to start by testing the water quality. If the test indicates that there is a high level of nitrite or ammonia, carry out a large water change to reduce the amount of toxic materials. Make sure the new water that is being added to the tank is conditioned properly. Remove toxins such as chlorine, and adjust the water temperature. If the water is not conditioned properly, it can add more stress to the fish.

Poor nutrition is another common cause of hole in the head disease. Improper diet can lead to vitamin and mineral deficiencies, and eventually a weakened immune system. A healthy nutritious diet is vital for a strong immune system. A variety of quality pellet food and fresh food would be ideal. You can also add vitamin supplements to the water regularly, or soak the fish food in vitamin supplements before feeding.

If the hole in the head disease have progressed, simply improving the water conditions and feeding better fish food may not resolve the issue. Metronidazole, or Flagyl, are often used to treat hole in the head disease. Metronidazole is known to be effective in treating Hexamita. As described by the Florida Museum of Natural History, the protozoan Hexamita is the cause of “hole in the head” disease.

Oscar Fish Lifespan

Oscars have a long life expectancy. They can live as long as 20 years if taken care of properly. If you decide to keep an oscar, be prepared to take care of it for many years. Since oscars have a personality, many owners become attached to their fish over the years.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the fish care tips that we've picked up along the way. Our goal at Fish Laboratory is to keep publishing accurate content to help fishkeepers keep their fish and aquarium healthy.

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Oscar Fish Care Guide by Fish Laboratory