Oscar Fish: A Comprehensive Guide

The Oscar Fish is a freshwater fish unlike any other. It has a dark side to it behaviourally but in the right setting, it makes for a great pet. It is intelligent, personable, has great looks, and has a long lifespan. It may not be the easiest freshwater fish to keep but it is definitely up there when it comes to the joy and company a pet can provide. Here is everything you need to know about this interesting fish.

At a Glance



Where Do Oscars Live?

This fish is indigenous to the Amazon River basin in South America. It can be natively found in Brazil, Colombia, Ecuador, Guyana, French Guiana, Suriname, Peru, and Venezuela. 

They are generally found in slow-moving waters and can often be found sheltering under submerged plant matter.

As a by-product of their hardiness and popularity, viable populations now exist in non-native countries such as China, India, Australia, and the USA where they were inadvertently released from the pet trade.

Oscar Fish Physical Description

These fish have oval-shaped bodies with a lot of girth which makes them heavy. They have unique markings on their bellies and come in various colours depending on the variety (more on this later). The fins have the typical robust shape common among Cichlids. They have large mouths. The males and females have very few differentiating features.  

Are Oscars Great As Pets?

As everyone seeks something different from their pets, I will list all the unique characteristics of this fish and hopefully, that will help you decide if it is an excellent pet for you

• It is one of the most aggressive freshwater fish and will occasionally even go after its owner during tank maintenance. The latter is not a cause for concern as their teeth aren’t strong enough to hurt humans but it can be pretty startling
• They can grow to be as large as 18 inches or 45 cm. This necessitates a huge tank especially if you want to keep a group of these fish. They also grow very rapidly
• They will regularly throw the substrate and hardscape around and this can be noisy and annoying, especially at night. On the plus side, they are very playful and have an almost puppy-like demeanour towards their owners.
• They can live for nearly twenty years
• They produce a lot of waste and need a very robust filtration system
• They are fairly hardy and can tolerate a few lapses in tank maintenance and upkeep provided these lapses are fixed quickly
• They are very difficult to breed in the home aquarium
• They will aggressively rearrange the tank’s substrate and decor which pretty much eliminates the possibility of having live plants in the tank
• They are readily available and relatively inexpensive
• They are very easy to feed
• Unless the water conditions become pathetic, these fish will rarely contract any diseases
• These fish are accomplished jumpers. You will need a tight-fitting lid that can be weighed down to avoid any mishap

How Big Can Oscar Fish Get?

In a large enough tank, with a proper diet and good water conditions, Oscar fish can grow to a maximum size of between 10 inches and 14 inches or 25 cm to 35.5 cm. In some rare cases, they can grow to be as large as 18 inches or 45 cm.

They also grow very quickly. A juvenile can grow at a rate of an inch a month and can reach its adult size in less than a year. This means that you will have to start out with a tank large enough to accommodate the adult size of this fish as otherwise, it can lead to stunted growth and over-compacting of its internal organs leading to an early death.

Oscar Fish Behaviour and Temperament – Its Dark Side

The Oscar fish is native to water bodies that are also home to some of the most ferocious freshwater fishes in the world. This can occasionally include piranhas which is why the Oscar fish is naturally aggressive. 

They are very active and quick too. This makes them lethal for anything that can fit in their mouths irrespective of how quick it is. Since adult Oscars have large mouths, the number of fish that can co-exist with Oscars without getting eaten is very low.

Having said that, these are social fish and should never be kept alone. They should be kept in groups of between 2 and 6 depending on how large the aquarium is.

Their most noteworthy personality trait is that each Oscar will be different. Some will be more aggressive than others and a rare few can be a real menace. Starting out with 4 to 6 juveniles or getting a bonded pair are good ways to establish a working hierarchy.

Oscar Fish Tankmates

Considering the size and temperament of the Oscar fish, it is best to keep a species only tank. However, if you really must keep other fish then your options include

• Jack Dempseys
• Black Convicts
• Green Terrors
• Firemouths
• Large Plecos
• Arowanas (illegal in many places so check your local laws)

All these fish are large and produce a lot of waste. You will need a massive tank to house them with Oscars. However, if you looking to set up a monster tank then a community aquarium with these fish would be perfection.

As mentioned earlier, some individuals might have a particularly mean streak and these fish can start a fight to the death with one of the tankmates. When adding other fish, monitor each Oscar closely and remove any fish that is being too hostile.

Are Oscar Fish Intelligent?

There is some debate regarding how intelligent these fish are. The consensus among hobbyists is that they are among the most intelligent freshwater fish out there. Many Oscars will learn to recognize their owners and will interact with them. Some hobbyists have even reported being able to hand-feed these fish.

My experience is that it can vary from fish to fish. They are generally very personable, and I have had individuals that would play around like puppies. This included adorable belly flops and playful mannerisms. 

Another aspect about these fish I can confirm is that they can become depressed if kept alone. At least another Oscar in the tank with plenty of interaction from the owner tends to keep these fish in a happy space.

Aquarium Setup For Oscar Fish

Aquarium Setup The Oscar fish is a large and active fish that produces a lot of waste. All these must be taken into consideration when sting up the aquarium. Here are all the specifics

Tank Size

This is the most important consideration when keeping these fish. Since the adults can grow to be more than a foot or 30 cm long, and there needs to be a minimum of two of these fish, the tank must be massive. For a pair, at least a 100-gallon tank is needed. Each additional Oscar will need an extra 75 gallons. The same goes for any other tankmate. Since it produces copious amounts of waste, the larger the tank, the better it is.

The Lid

The aquarium needs a tight-fitting lid as these fish are notorious jumpers. Part of their diet in the natural habitat consists of low-hanging vegetation and insects they pluck out from just above the water’s surface. Water droplets or debris on the underside of the lid can be mistaken for food and that can initiate a similar jumping response.

Just having a lid isn’t enough as their large size and weight can knock the lid off completely which is why it needs to be weighed down. 

There shouldn’t be any sharp edges on the underside of the lid to avoid injuries. I have found that adding a lightweight piece of transparent plastic roofing sheet on top of the aquarium and below the lid creates an effective barrier that keeps the fish safe.

Lighting

The lighting should be moderate as intense lighting can wash out the Oscar fish’ brilliant colours and markings. Light fixtures should be attached in such a way that there are no sharp edges or corners to avoid injuring any fish that might jump.

Filtration System

After the tank size, the filtration system is the most important part of the tank setup. Oscars and all the other fish that are compatible with them poop a lot. This puts a lot of strain on the filtration system. A very robust and reliable filter is needed to take this bioload.

I prefer a canister filter that is rated for four times the volume of water in the tank. Brands like Eheim and Fluval make great filters. The advantage of using a canister filter is that it provides mechanical, biological, and chemical filtration in a single setup while being easy to maintain.

Other Equipment

While the filter will introduce a water current in the tank, I like to add a couple of wavemakers. These keep the water nicely oxygenated. They also introduce a moderate amount of water flow which these fish seem to enjoy.

Multiple heaters are needed to keep the larger aquarium at a stable and uniform temperature.

Substrate And Decor

As mentioned before, these fish love to reorganize their tanks. I do not recommend adding live plants although Anubias that are strongly rooted to a piece of decor can survive in a tank with Oscars. As for the decor itself, I like to use aquarium-safe glue to anchor everything I want to stay in place before adding the substrate. 

For the substrate, go with something that has a large grain size and doesn’t have any sharp edges. Oscar Fish will dig trenches, move the substrate around, and keep changing the scenery inside the tank. This applies to any hardscape element that isn’t anchored to the base of the aquarium. As such, you need to be a bit fluid with the visuals of the tank. 

Watching these fish cart things around and rearranging everything multiple times a day is one of the unique appeals of keeping them after all.

Keeping the substrate depth at under 2 inches makes cleaning it a lot easier.

Ideal Water Parameters For Oscar Fish

The ideal water parameters for the Oscar fish are as follows

The important thing here is to keep things as stable as possible. Sudden and large changes in the water parameters even within the range mentioned above can stress Oscars making them susceptible to diseases and infections.

These fish do recover very quickly if you can correct any fluctuations promptly.

Oscar Fish Aquarium Cycling & Maintenance

While Oscars are pretty hardy, they need a properly cycled tank. Even small amounts of Ammonia and Nitrites can make them very sick very quickly. The best way to cycle a new tank is by getting some used filter media and substrate from a mature tank. You can also get beneficial bacteria starter kits at most fish stores. Either of these options will kickstart the cycling process.

Testing is key to ensuring that the tank has cycled properly. The three key chemicals to test for are Ammonia, Nitrites, and Nitrates. Once the tank is set up and all the equipment is running, add a tablespoon of fish food every day. Keep testing the water. 

Initially, there will be a lot of ammonia. Eventually, it will start dropping and it will be the turn of Nitrites to spike. With time, Ammonia with reach zero ppm and Nitrites will reach its peak. Following this, the Nitrite level will start to fall and eventually become zero as well. Once no Ammonia or Nitrite is detected, and only Nitrate is present, do a 30% water change. Keep testing for a few more days. Do another water change after 5 days. Test again to ensure that Ammonia and Nitrite are zero, and Nitrate is under 10 ppm. The tank is ready to accept the Oscar fish.

Once the fish are added, the bioload on the aquarium’s filtration system will increase a lot. Keep testing to ensure that everything stays stable and within the safe range.

Maintenance of an Oscar fish tank consists of

• 30% water change every 10 to 14 days
• Using a gravel vacuum to clean the substrate during every water change
• Cleaning the filter once every three months
• Swapping out half of the filter media once every six months
• Scraping off excessive algae once a month

Aquascaping An Oscar Fish Tank

Given the tendency of these fish to uproot everything, the options are very limited. Plants like Anubias nana and Java Fern that can be attached to hardscape elements are pretty much it when it comes to viable live plants. Even these plants must be kept in a different tank until they are strongly rooted in whatever they are attached to and even then, the Oscar fish could just rip them apart.

Artificial plants offer a nice compromise and also act as great playthings for these vivacious fish.

Hardscaping An Oscar Fish Tank

Hardscaping an Oscar fish tank is straightforward. Add rocks, pebbles, driftwood, and artificial decor items and leave it up to the fish to constantly arrange and rearrange everything. If there is a particular hardscape element that you really want to stay in a specific spot, then glue it down to the bottom of the tank when setting the tank up. 

If you plan on keeping other fish with the Oscar fish, then consider fixing a few large hiding places as well. This will offer shelter to any fish that gets targeted and will diffuse the aggression to a certain degree.

Oscar Fish Diet and Feeding

Oscars are omnivores and need a balanced diet that is high in protein. I like to give them a combination of any high-quality fish food specifically formulated for South American Cichlids combined with live or frozen Bloodworm and brine Shrimp. Frozen peas and algae wafers take care of their Vitamin C and fibre needs.  

The occasional feeder fish can be used as treats but be very careful as these can be a source of infections and parasites.

Oscars will almost always eat every time you offer them food. So, it is your responsibility not to overfeed them. I get the best results when I feed my Oscars twice a day with just enough food that they can finish off in under three minutes.

Oscar Fish Health Problems & Disease

Oscar fish are generally resistant to diseases and infections. Good water quality is the key behind this. Sometimes, changes in the water parameters can cause their immune system to get disrupted and this can lead to diseases like itch and fin rot. Fixing the water quality will usually allow the fish to fight such diseases on their own. In extreme cases, you can use over the counter medication available at most fish stores.

One disease that you need to keep an eye out for is Hole in The Head disease. This too can be treated with medication meant for HITH. A good diet and stable water conditions will keep this disease at bay.

Quarantine any feeder fish or new additions to the tank to avoid introducing diseases.

Oscar Fish Breeding

The Oscar fish is one of the most difficult fish to breed in the home aquarium. It is very difficult to sex them and even if there is a confirmed male and female in the tank, they don’t end up bonding very easily.

Another challenge is that these fish become a lot more aggressive than normal during breeding which is saying a lot given their natural temperament.

You can try to breed them by either getting a bonded pair or by starting off with a bunch of juveniles and getting lucky with a pair of them bonding naturally.

This bonded pair can then be moved to a breeding tank that has a lot of flat rocks for the fish to lay their eggs. Simulate the rainy season by doing daily water changes and slowly bringing the temperature down.

The fish may mate, and the female will then lay about 3000 eggs on the flat surfaces. Oscars are good parents and will take care of their young. The water quality in the breeding tank must be pristine as the slightest misstep can disrupt the entire process.

Did You Know All These Cool Facts About Oscar Fish?

• Even though they are native to the Amazon River basin in South America, feral populations now exist in rivers and lakes in China, India, Australia, and the USA.
• In their natural habitat, they jump out of the water to attack and eat insects that rest on low-hanging branches near the water surface
• They are considered as one of the smartest freshwater fish
• They have two sets of teeth. One in their mouth and one at the back of their throat. For those wondering, neither set is strong enough to cause any real damage to humans
• They can grow at a rapid rate of an inch a month
• Each Oscar fish has a unique personality, and some can even be coaxed into playing dead
• They can survive without food for a month
• They will actively rearrange everything inside the tank that isn’t glued down

Oscar Fish Colours

There are many different colour morphs of the Oscar fish and new ones keep popping up. Some of the most commonly available ones are

Tiger Oscar: This is the most readily available type of Oscar fish out there. It is predominantly dark grey or black with bright orange stripes across its body giving rise to its name.

Albino Oscar: These are predominantly white with red eyes and red stripes on their body.

White Oscar: This variety looks very similar to an Albino Oscar but with dark eyes and no or very light stripes on its body.

Red Oscar: The Red Oscar is like a much more intensely coloured Tiger Oscar. This fish is mostly black with the stripes being a stunning red.

Black Oscar: The back Oscar is pretty self-descriptive. It does not have the markings that the Tiger Oscar has but the rest of it is pretty much the same.

Green Oscar: This too is like the Tiger Oscar but with a predominantly moss-green-coloured body with orange stripes. This is one of the more difficult Oscars to find.

Blue Oscar: Another very exotic variant is the Blue Oscar which has a powder blue colouration with orange and pink markings.

Other more exotic Oscar varieties include Lemon Oscar, Veil tail Oscar, Blueberry Oscar, Lutino Oscar, Florida Oscar, and Golden Oscar.

Oscar Fish FAQ

Is Oscar fish a good pet?

It is an aggressive fish that needs a very large tank. It is fairly hardy though and quite personable with a long lifespan. If these are things that you are looking for then it can be a great pet

What size tank do Oscars need?

1 Oscar – 60 gallons (not recommended as these are social fish)
2 Oscars – 100 gallons
Each additional Oscar – An extra 75 gallons

Which fish can live with Oscar?

Other Oscars, Jack Dempseys, Black Convicts, Green Terrors, Firemouths, Large Plecos, and Arowanas

How often should you change Oscar water?

Once every 10 to 14 days

Do Oscars need to be in pairs?

Yes

How often do you feed Oscar fish?

Twice a day

How can you tell male from female Oscars?

It is very difficult to tell the sexes apart. A close inspection of the genital area for the presence of an egg tube is one way although this needs an expert’s eye. DNA testing is the surest method

Which Oscar fish is best?

All Oscars are great as long as you can properly care for them. Go for the one that visually pleases you the most while being within your budget

Can Oscars recognize their owners?

It is believed that they can recognize their owners

Do Oscars like to live alone?

No. They are social fish that need the company of other Oscars

How long do Oscars live for?

Up to 20 years with good care

Do Oscars like sand or gravel?

They are fine with either

How big do Oscar fish get?

Oscar fish usually grow to a maximum size of 10 to 14 inches or 25 to 35.5 cm. There have been reports of them reaching sizes of up to 18 inches or 45 cm

Can you eat Oscar fish?

Oscar fish are edible and are a part of the local diet in their natural habitat. However, unless you live near the Amazon River basin, it makes more sense to eat whatever fish is commercially available in your local fish market

How many Oscar fish can stay together?

The upper limit totally depends on the size of the tank

What is the best food for Oscar fish?

A high-quality fish food specially formulated for South American cichlids supplemented with live or frozen bloodworms, shrimp, peas, and algae wafers

How can I make my Oscar fish grow faster?

Provide them with a proper diet and maintain good water quality

How long can Oscars go without food?

About a month but this should be avoided

Can you overfeed Oscars?

Yes. They will keep eating as long as food is available

How many times a day should I feed my Oscars?

Twice a day

How can I improve my Oscar fish color?

A healthy diet and good water quality

How do I keep my Oscar fish tank clean?

Install a robust filtration system and do a partial water change at least once every two weeks

Do Oscars like light?

They prefer moderate lighting with places in the aquarium that offer shade

Are Oscars happy alone?

No

Conclusion

The Oscar fish is unique in many ways. It has some very specific requirements such as a very large tank and proper maintenance. It also offers a lot in return in the form of its personality and looks. It is challenging to keep but in a very straightforward manner.
If you can meet all their specific requirements, the Oscar fish will provide years of entertainment and company while ensuring that you always find the hobby interesting and captivating.