Oscar Fish – Ultimate Guide for Care, Breeding, and Tank Setup

My 18 Inch Male Tiger Oscar

Oscar fish can be found naturally in the Amazon region of South America. They are among the most intelligent and attractive tropical fishes in the world. Their intelligence, appearance, and colors are among the reasons they are kept domestically. In fact, they are very smart and can be trained easily to perform humanlike tricks.


Interestingly, Oscar fish is very temperamental which is the reason they are to be raised by experienced persons only. They can eat just any type of food that is common among humans although finding a tank mate could as well be difficult. They often produce huge waste in a short time which implies you’ll endeavor to clean the tank regularly as well as put the necessary filtration system in place.

In this article, we will take you through everything you’ll need to know about the Oscar fish including its captivating behavior, breeding, size, and much more.

Fish Profile
Latin NameAstronotus ocellatus
Native HabitatTropical South America
Care DifficultyModerate
Lifespan10 – 15 years
BehaviorTerritorial & Aggressive
SizeAt most 12 inches


The Oscar which is also called Astronotus ocellatus belongs to the cichlid family which thrives in the tropical region of South America. When kept in the right dwelling place, it can survive for about 10 to 15 years. They are to be placed on the proper diet in a comfortable aquarium with a good filtration system. With all these in place, they will be able to enjoy a good long life.

They are often eaten among the local of South America making it one of the most widely sold species of fishes in the area. In Europe and in the US, it is very popular for aquarium because of its extraordinary attractiveness and behavior.

Oscar fish is very different from other fishes, and it’s among the favorites to be kept as pets. It grows to a size that will attract your attention making it one of the biggest freshwater fishes out there.

If you’re interested in raising species of fish with beauty, diversity of food, and intelligence which are some of the common characteristics of humans, the Oscar fish is the choice to make.


Oscar fish is among the fishes that we say to be aggressive. However, it is out of place to say they are outrightly hostile to other fishes living with them. Just they are cichlids, and they have the tendency to be aggressive and territorial even towards her kind.

The level of aggression and intolerance can be minimized by creating a suitable and sizable aquarium. An adult Oscar should take at least 55 gallons and if you intend to increase the number of fishes in the aquarium, then you should consider increasing the size of the aquarium as well.

Identifying an Oscar with signs of aggression can be easier than you had thought. You will observe that most of them will open their mouths very widely with an enlarged gill which will make their head to appear bigger. Once you sight this, it is important to tread with caution to save yourself from being harmed.

In most cases, Oscars are not very happy during tank maintenance activities especially when you dip your hands. However, Oscars seldom hurt their owners, but their sharp teeth can create a tear. So, the tank should be kept from the reach of children so they may not have to lose a finger.

Signs of aggression are very different from the rituals of breeding. Nevertheless, you may find it difficult trying to differentiate between the act of mating or courtship behavior and aggression. As we continue in the article, you’ll have a clearer picture of the temperament of an Oscar during its breeding period.

Distinguishing between male Oscar and female Oscar

If you’ve been relying on colors to tell which is female or male, then you may have been guessing wrong. The major way to differentiate the two is by observing the shape of their genital papillae.

The genital papillae of a 4 to 5 inches long Oscar are wide enough to be seen without using any special instrument. Fortunately, you’ll see that they are pointy in males while they are wide and blunt in the female Oscars.

Types of Oscars

Some of the varieties of Oscars which have been bred from their natural habitat include.

  • Tiger Oscar – They are the most common and the closest in terms of resemblance to the original species whose habitat is in the wild.
  • Red Oscar – Just as their name implies, they are reddish in color which makes them appear very beautiful in the tank. They were first bred in the early 1970s.
  • Albino Tiger Oscar – Think of a pedantic fish then you’ll get the overall picture of this fish. They have some color pigmentation which makes it different from the real albino fish. With some Tiger Oscar fish in it, they’re a must-have in the aquarium.
  • Albino Oscar – Naturally, they have no color pigmentation. They’re the real albino Oscar fish with a clear and speckle less body.
  • Red Lutino Oscar – While some persons may refer to it as an albino Oscar, we’ll stick to its name which is the real Red Lutino Oscar fish.
  • Veil Tail Oscar fish – The breeders intended to getting an Oscar fish with long fins and they succeeded. They appear very beautiful, but the long fins can break easily which might shorten its lifespan.
  • Wild Oscar fish – This is the Oscar that is taken from its natural habitat in the fresh waters of South America. They are natural and every other type can be traced to it.

There are other species of Oscars with some unique characteristics even though they’re rare. An example is the Lemon Oscar which was first introduced in the Philippines. They are very beautiful with some unique traits which can often be found in the wild Oscar fish.


It is important to have an idea of the color of the Oscars in their natural environment. Yes, they have ringed spots in their dark bodies. These spots are referred to as ocelli and can be found on the dorsal fin and the caudal peduncle. Thanks to their orange lines and white curves.

Oscars can change their colors at will as a means of survival and adaptation. The young ones tend to exhibit different colors more than adults.


As we had said earlier, Oscars have teeth in their mouth for feeding and adaptation. They may not be as sharp as a knife but it can create a deep cut. They have jaws which hold the teeth in position and some pharyngeal teeth along the throat.

Interestingly, the teeth in the jaw are small and comes in handy when grasping its food while the teeth that are found in the throat helps in processing the food as well as the prey.


The life and health of an Oscar fish can be prolonged with the right diet. They should be fed properly with foods like insects, crayfish, and worms which are rich in protein. It is important to know that the Oscars require high concentrates of Vitamin C. So, you can supplement their vitamin supply by providing them with fresh fruits.

Oscars have green plants and algae as their major diets too which is very much present in their prey. Giving dried foods to Oscars can be harmful to their digestive system even though they have a penchant for them.

Thus, they should be offered dried foods that contain probiotics since they help to mitigate the occurrence of constipation which could lead to its premature death. In as much as dried foods are important for its growth, food supplements with good moisture content will help boost its immune system. They include vegetables and fresh fruits.

Preferred food

It is important that we provide you with details of food that is required by an Oscar fish. You should not be confused with its diet as this is a closer look as to how the food is administered.

The best regimen for Oscar fish is a combination of processed food and live food. It is important to ensure that the Oscar can ingest the food comfortably by considering its size of mouth in comparison with the size of the food.

Oscars that are living in the wild can eat just any type of food such as crustaceans and insects. Live foods are very helpful in terms of enhancing their growth rate but the problem is that they should not be taken in excess since they can cause obesity and other parasitic attacks.

Occasionally, mussels, mealworms, and prawns can be introduced in their diet. If you have access to a healthy feeder fish, then it’ll be a good idea to feed your Oscar with it. Possibly you can raise your feeder fish to prevent getting a diseased feeder from the store.

It is very easy to get processed foods from the stores which include blood worms, brine shrimp, beef heart, and jumbo krill. The main condition is that they must be small enough for Oscar’s mouth.

It is important to watch as the food is being taken by the Oscars as they tend to leave some behind which can contaminate the water. It has been established that most cichlids tend to thrive when fed with peas. You can try this yourself, we’re certain you will experience positive results as well.

Fruits from tropical South America can be an excellent choice for the Oscars but the only disadvantage is that they are seasonal meaning you may not find it very often especially if your fish has fallen in love with them.

Moreover, Oscars are predatory which implies they can easily digest meat. So, you can add meat occasional to its meal. To keep your Oscar fish healthy and happy, you’ll have to offer it different varieties of food every day.


Have you ever experienced any difficulty trying to breed a fish in captivity? Guess the Oscar fish can be a little harder. Just as humans, Oscars tend to be very selective with mates. With this, it is impossible to assume that you can easily breed by just putting two mature male and female Oscars together.

You can overcome this difficulty by buying an established mating pair from the fish breeding stores. You can also consider buying a group of young Oscars so they can form a mutual relationship as they live and grow together.

It is important to know that you’ll have to wait for the juveniles to mature before they can start mating and this may take more than a year if you are going by the third option. The good thing is that they can breed easily irrespective of the variety once the connection is established.

The best time for Oscar fish to breed is the rainy season. You can create an artificial rainy season in your tank by decreasing the water temperature. Another method is to change some of the water regularly or sprinkle some water on the surface every day.

So how do you know when they are ready to mate? You’ll notice that they will flare the gills and fins to attract their partners. The couples will prepare a suitable place to lay the eggs. In most cases, it’ll be on a clean rock surface. Some of the females can lay over 3000 eggs at a time.

It will be the responsibility of the parents to safeguard the eggs by protecting them from external attacks until after 2 to 3 days where they will hatch.

To enhance the survival of the juveniles, it will be necessary to take them to a different tank with a good filtration system. Food is very necessary for their growth at this time. So, they are to be placed on a healthy diet. They must be supplied with food at least two to three times a day.

As they mature gradually, you will have to take them to a comfortable tank to guarantee the possibility of their survival.

Tank set up

Oscar fish are ranked among the largest freshwater aquarium fishes in the world. In most cases, they can grow to lengths of 12 inches and above. With such a size, you will be required to build a tank that will accommodate them comfortably.

A 75-gallon aquarium can only contain one or two Oscars at a time. This is because as the fish grows bigger, it will require enough space to enhance its movements. Thus, the larger the tank, the better the wellbeing of the fishes.

Ensure that your aquarium is placed on a platform where you can easily sight the movement of the fish in the water. The tank should be leveled on the platform to prevent undue pressure on its sides which may lead to leakage.

Oscars tend to jump and we have heard stories of some that had leaped to death. Thus, your tank should be well shielded to protect the fish against fall.

Minimum Tank Size Per Fish: 40 Gallons / 151 liters

Recommended Tank Size: 75 Gallons / 284 liters

Filtration system

You need to add a good filtration system to enhance the quality of your tank’s environment. Oscar fish often generate much waste which makes it essential to include a good charcoal filtration system in your aquarium. The purpose of this filter is to keep the water clear of solid waste like food particles.

Another importance of the filter is to maintain the pH level of the water by controlling both biological and chemical agents. Finally, it will make more oxygen available in the water which is very essential for the survival of the fishes.

Ammonia is generated during the fishes’ excretory and respiratory activities and if the water becomes saturated with it, it could lead to water poisoning and eventual death of the fishes. So, ensure that you get the best filtration system available.

Maintain your filters in accordance with the instructions from the manufacturer. And at no time should the filter fail to function properly while the fish is still there. Moreover, a minimum of 10% of the water in the tank should be changed at least once a week.

Water conditions

Fine-grained substrates like sand are placed at the bottom of the tank to enhance the living condition of the fish. The reason we recommend fine sand is because they will not be hurt the Oscar as it digs its way deep into the sand.

Moreover, you can decorate the tank with bogwood or rocks. This will serve as a hiding place or territory for each of the fishes. The woods must be fixed to the tank to make it more natural and would not dislodge easily as they dig around it.

Oscar fish may not eat live plants but you would not have to plant them. There’s the likelihood that the plants will not survive the rigorous stress from the fish. You can decorate your tank with hardy plants since they can withstand the stress. Another option is to use floating plants since they are not easily uprooted by the fish.

The healthy condition of the water can be maintained by using a good quality filter and a heater. The purpose of the filter is to remove harmful chemicals from the water while the heater helps to maintain the temperature. Moreover, you can use some lighting systems in place of a heater. Lighting up your tank will enhance the appearance and beauty of the fish.

Any equipment that is in the tank must be fixed firmly so they will not yield easily to the trauma from the fish. Meanwhile, there will be no need for a water pump to create an artificial current since the filtration system will provide the waves.

Diseases and Treatment

The common diseases of the Oscar fish are bloat, ich, fin and tail rot, Popeye, and vulnerable head. These diseases tend to multiply as the tank becomes overcrowded and the quality of the water drops.

The vulnerable head disease is mostly compounded by poor water quality. In this disease, you will observe the presence of pits or cavities in the head and face. Another cause of this effect is the deficiency in phosphorus, calcium, Vitamin D and Vitamin C.

We had discussed extensively on the importance of a high-quality diet for the growth and survival of your fish. Poor feeding practices will lead to its malnourishment which might reduce its immunity over diseases.

The use of certain chemicals for filtration can lead to changes in the water pH as well as its level of oxygen. These factors can lead to many of the diseases we have listed above.

You must check your Oscar fish periodically for diseases and injuries. It is necessary that you enhance your knowledge of various categories of infections that might affect your fish. With this, you will know the right manner to tackle each infection based on its symptoms. Most importantly, you should stick to practices that will reduce the spread of diseases in the tank.

Hole in the head disease can be treated with Flagyl or metronidazole. You’ll have to add this to the aquarium which the fish will bathe in it for about 24 hours.

Ich which is caused by a protozoan parasite called Ichthyophthirius multifilis can be treated with malachite green, salt, and copper sulfate.

Fin and tail rot which causes some portions of the fin to fall off can be treated with tetracycline, chloramphenicol, or oxytetracycline. 

Meanwhile, Popeye disease which is often caused by poor water conditions will produce symptoms like bulging eyes one both or single eyes. It can be treated by enhancing the quality of the water.

Bloat or dropsy is among the most serious diseases in Oscars. It is often caused by constipation or overfeeding. Some of its popular symptoms include erratic swimming, bloated appearance, hard excreta trailing the Oscar, and absence of bowel movement.

You can treat constipation by reducing the quantity of food supplied and then change some conditions of the water especially the temperature. We recommend you to raise the water temperature by a maximum of two degrees.

Oscars are very friendly and healthy. All you need do is to pay attention to its food supply as well as the condition of its environment. Try to observe your Oscar regularly so as to respond promptly to its health needs.

Tank mates

Oscars are not very friendly with other species. As we said earlier, Oscars are often very aggressive on other tank mates and if they do not kill them at first sight, they will be made to live in fear.

The natural habitat of the Oscars can accommodate diverse species of fishes making them adapt easily. However, this cannot be said about Oscars in the tank environment. In order to prevent tensions, it is advisable to keep a single Oscar in a tank.

You should never introduce any small fish in the tank as they will not survive to tell the tale.

Nevertheless, you can still house a bigger and tougher fish in the tank only if it will not endanger the life of your Oscar fish. However, the mate must be a member of the cichlid family. Some of the recommended ones include Bichirs, Green Terrors, Arowanas, Jaguar cichlids, silver dollars, jack dempseys, and severum cichlids.

Maintaining Oscar tanks

The job of maintaining a healthy environment for your Oscar fish may not be as easy as you think. This is because cichlids tend to produce more waste in a very short time than other families of fishes. So, you got some work to do.

Moreover, you will have to keep your filtration system in good condition at all times and as well maintain a balanced pH, nitrate, and temperature levels.

The magnitude of waste that is produced by the fish will require that you clean the tank regularly. The nitrate level should be at a maximum of 40 ppm (anything beyond this will be hazardous).

Oscars are originally from warmer climates which implies they will enjoy the tank if it feels warm. You can keep the temperature at 72°F to 77°F. Ensure that you set the tank heater to the appropriate temperature. Try not to use glass heaters since they can be easily broken by Oscars.

You can contact an aquarium technician to guide you on the best methods to maintain your Oscar tanks.


How big can Oscar fish grow?

The biggest Oscar fish can grow to approximately 18 inches. It is among the biggest freshwater fishes in the world. The rate of growth of the Oscar fish is very fast, sometimes at the rate of 8 inches in 10 months.

The largest Oscar fish can reach a length of 22 inches while the giant species will reach around 17 to 18 inches.

Do we have a dwarf Oscar fish?

Yes, we do but they are not easily found. In most cases, they are crossbred to create a shorter and more compact Oscars.

How do you measure the size of an Oscar fish?

By attaching a string or ruler on the glass of your tank, you can get the approximate measurement of the size of your Oscar fish. The good thing about this method is that you will not have to take the fish out of the water.

What is the main food for an Oscar fish?

Oscars are generally omnivorous. This means they will eat virtually anything that can be taken by humans. Wild Oscars survive by eating insects, live fish, crustaceans, and some dead plants. You can feed them with fruits to supplement their vitamins.

What is the lifespan of an Oscar fish?

Oscars live up to 12 years. However, under healthy living conditions, they can live as long as 15 years.

What is the hole in the head disease like?

This is a disease which is common with freshwater cichlids. It is also called Hexamita with symptoms like loss of appetite, stringy feces, and faded color. In most cases, the disease will lead to lesions on the body and the head. It is often very fatal and has been compounded by poor water conditions.

Do Oscar fish have a personality?

The Oscar is among the most intelligent fishes in the world. They have various traits with humans and that includes a personality. It can recognize its owner just like most like dogs and cats can.

What are the best foods for the Oscars?

You can supply your Oscar fish with brine shrimp, Hikari cichlid gold, bloodworms, mealworms, beef heart, and tetra jumbo krill.

How does Oscar fish fall asleep?

It is common for you to think that fishes do not sleep since their eyes are always open. However, no fish is born with the ability to shut the eyes. Fishes all over the world will often rest for some part of the day. Oscars are not an exemption to this fact. You’ll observe that your Oscar will be motionless for a while that is to say she is sleeping at that time even though the eyes are open.

What fish will live with an Oscar fish?

Suitable tankmates for an Oscar fish should be either large or spiny fishes. They include jaguar cichlid, Jack Dempsey, green terror, sailfin pleco, and other cichlids. Any other species that are not in this category will either be eaten or will live in fear with the Oscar fish.

How many eggs can a female Oscar lay?

Within a few days, a female Oscar will produce at least 3000 eggs. It is unfortunate that not all of them will make it.

What is the best pH level for Oscar fish?

It is important to ensure that the pH of the tank is the same as that in the wild. Your Oscar will thrive at a pH level of 7.2. You can use a water pH level test instruments to measure the actual pH level of the water. You can apply a water conditioner or a cichlid buffer as the case may be.

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