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

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Common Name(s)Oscar Fish, Tiger Oscar, Oscar Cichlid, Velvet Cichlid, Mabled Cichlid, Water Dog
Scientific NameAstronotus ocellatus
OriginSouth America
Temperature72-80 °F (22-27 °C)
Size8-16 inches
Minimum Tank Size55 gallons
FoodOmnivorous diet (pellet food, freeze dried shrimp, live worms, peas, etc.)
Lifespan20 years
Water pH6.0-7.5
Tank MatesPotential tank mates include Firemouth, Jack Dempsey, Common Pleco and Clown Loaches.
BreedingBreeding pair spawn eggs during rainy season
DiseaseMay be susceptible to Hole in the Head disease.
Oscar Fish, Astronotus ocellatus
Oscar Fish (Astronotus ocellatus)

Oscar fish (Astronotus ocellatus) is a type of South American Cichlid, due to their adaptability and popularity in the aquarium hobby, they can can be found worldwide. Within the aquarium trade, Oscar fish are also known as Tiger Oscar, Oscar Cichlid, and Velvet Cichlid, among many other names.

The popularity of Oscar fish in the aquarium hobby can be attributed to both their appearance and behavior.

First, they are attractive fish with a striking appearance. Tiger Oscars with the black body and orange patterns are truly stunning, and it is easy to understand why they are so popular. In addition, there are many other varieties of Oscar fish such as Red Oscar, Albino Oscar, Lemon Oscar, Black Oscar, Blue Oscar, Veil Tail Oscars, and more. Each variety is uniquely beautiful, which is another reason why many fishkeepers are attracted to this fish.

Next, their interesting behavior is another contributing factor to their popularity in the aquarium hobby. 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, also known as caudal fins. To many owners, this resembles a puppy wagging its tail and this is why they are nicknamed “Water Dogs.” Since they have so much personality, many fishkeepers become very attached to them as a pet fish.

Unfortunately, Oscar fish are one of the most mistreated fish in the aquarium hobby as well. When they are sold at local fish stores, they are usually sold as small juvenile fish. Generally, they would be sold at sizes of approximately 2 inches (5 cm). Many people that purchase these fish do not realize that the fish could grow to a foot long (30 cm) within a year. Due to their fast growth rate and large size as an adult, they are often kept in aquariums that are too small for them.

3 Tips for Oscar Fish Care #shorts

Oscar Fish Care

Oscar fish are hardy fish that are easy to take care of. Even though they are large fish, they can even be kept by beginners in the aquarium hobby. With that said, they aren’t suitable for all fishkeepers either since there are certain care requirements that must be met. Having a large tank is one of these requirements.

Here are more specifics on how to properly take care of Oscar fish:

Temperature for Oscar Fish

The optimal temperature range for Oscar fish is 72-80 °F (22-27 °C). They will also survive in an acceptable temperature range of 68-82 °F (20-28 °C).

Since Oscar fish are tropical fish that are native to the Amazon River basin, they are these tropical temperatures are required. If the temperature drops too low, their immune system can weaken. This will increase the likelihood of infections and diseases. Regarding low temperatures, the lethal limit is known to be 12.9°C (55.22°F).

In contrast, if the temperature is too high, oxygen levels in the tank can become depleted. This can become a dangerous environment for the fish as well, and it should be avoided.

In order to maintain stable water temperatures, installing a reliable aquarium heater and aquarium thermometer is important.

Water pH for Oscar Fish

The optimal water pH for Oscar fish is 6.8-7.2. While this is the optimal range, these hardy fish can survive in a pH range of 6.0-8.0 as well. Oscars are naturally hardy fish, and the captive bred fish are known to have an exceptionally high tolerance for a wider pH range.

Keep in mind that pH range should be changed very gradually, even if it is within the acceptable range. In addition, the tolerance will vary depending on the fish, even if it is the same species.

Lastly, if you wish to breed Oscar fish, it is best to stay within the optimal pH range.

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 Tank Size

Since Oscar fish are large fish, tank size is an important factor to consider.

For a full grown oscar fish, 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. If you have a small tank, oscars are not the best choice of fish to keep.

Oscar Fish Tank Setup

Aquarium Filtration

A good aquarium filter, 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.

Aquarium Lighting

Oscar fish prefer moderate to low aquarium light. 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 fish 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 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 small 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. Brine shrimp is great for feeding juvenile fish as well.

Growth rate can affected by the feeding patterns. 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 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.

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 as tank mates for oscars. Similar to many other cichlid species, oscars 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. Oscar fish are not suitable for an community aquarium.

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 cichlid
  • Jack dempseys
  • 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. A canister filter with a high filtration capacity may be required.

Oscar Fish Diseases

Oscars are known to get bacteria and parasite infections. One of the common diseases in oscars 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 Types

Tiger oscars, red oscars, and albino oscars 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

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