The Complete Oscar Fish Care Guide: Types, Diet, Tank Mates…

Oscars are infamous for their aggression, which is hard to imagine since they swim so gracefully, but they prove that looks can be deceiving.

Those who are brave enough to keep them may initially be attracted by their appearance and colors, but quickly come to appreciate their intelligence and social behaviors.

These are temperamental creatures that should only be looked after by experienced fish keepers. As omnivores they’re easy to feed, but it can be hard to find suitable tank mates.

This is definitely a species worthy of a place in your home; their complex behaviors will captivate you for hours.

In our article we cover how to care for Oscar fish, including ideal tank setups, tank mates, breeding and much more…

Category Rating
Care Level: Moderate
Temperament: Aggressive/Territorial
Color Form: Various
Lifespan: Up to 20 Years
Size: Up to 12 inches
Diet: Omnivorous
Family: Cichlidae
Minimum Tank Size: 55 gallons
Tank Set-Up: Freshwater: Rocks and Caves
Compatibility: Large, Passive Fish

Overview

Oscar

Oscars (Astronotus ocellatus) are a species of cichlid, so it won’t surprise you that they’re from the Cichlidae family. Most cichlids are from either Africa or South America, these are from the latter.

They’re native to Brazil, Columbia, Ecuador, French Guiana and Peru. They can be found along the Amazon river and its surrounding areas, which is one of the most bio diverse environments in the world.

Wild populations have also been found elsewhere (in places such as North America and China), though they’ve only spread to these areas through the fishkeeping industry. These fish are very popular for home aquariums, but they’re not to be purchased without thought. They’re infamous for their aggressive and territorial behavior which can make them difficult to handle.

This is a species full of personality. A few different varieties have been bred which offer some different colors and patterns. Pick wisely because they can live up to 20 years if kept in good health.

You will find Oscars in most aquarium stores – a healthy individual can be found for under $10.

Typical Behavior

Oscars are territorial, so adding them to your tank can be risky.

They aren’t afraid to attack other fish and will do so if a fish encroaches on their territory. Mating and feeding times can also fuel their aggression.

Most of their time will be spent swimming in the mid-levels of the tank, though they’ll often head down to the substrate in search of food. You might see them uproot plants and decorations during this search, so everything in the aquarium should be secured down.

The good news is that if the tank is setup correctly and you choose the right tank mates, their aggression can be controlled.

Types of Oscar Fish

Group of Oscars

Most varieties grow to be large, reaching up to 12 inches. They reach this size quite quickly in their lifetime, growing one inch a month until fully grown.

They have a long oval body. The dorsal and anal fins extend along the body to the caudal fin, which forms a fan at the rear. You’ll find it difficult to sex this species as they’re monomorphic, which means that both sexes have the same appearance. It takes a close look at the genitals to tell them apart.

Classically these cichlids are covered in an assortment of irregular black and orange splotches (tiger Oscars), but colors may change over time.

Many varieties have been created through selective breeding.

Red and lemon Oscar fish have bodies that are almost completely solid red or yellow respectively. Their fins tend to be either black or white.

Albinos are another popular choice. You can get albino varieties for lots of species, people are drawn to the bold white that covers the entire body.

What Makes The Perfect Oscar Tank?

Remember, fish have evolved to live in their natural regions, so you need to set up your aquarium to replicate these natural conditions.

The freshwaters of South America are warm with a neutral pH, so Oscars can’t handle extremes in acidity or alkalinity.

Water flow tends to be strong since most populations are found in rivers like the Amazon. While the sunlight would be strong, the water wouldn’t be crystal clear so some of the intensity is lost as the light penetrates the water.

At the bottom of the river would be a soft substrate with rocks, debris, and vegetation scattered around on top.

It’s fairly easy to recreate these conditions in your tank.

Tank Conditions

At the base of the tank should be a layer of soft substrate. The softest substrates are fine-grained, so sand would be ideal. Oscars like to dig so a coarse substrate would scratch them.

The most natural look would be to place rocks and bogwood around the tank, but you’re free to choose any decorations. Make a couple of caves for each fish so that they have somewhere to hide away within their territory. Also remember to firmly fix the decorations in place.

This species will dig around objects when looking for food which can dislodge them.

Live plants are unlikely to be eaten, but they’re still not safe. Just like the decorations, plants may be uprooted while they dig through the substrate.

Use hardy plants so they can survive the trauma. Floating plants should be safe from damage, a good option is hornwort.

Ideal water conditions are in the range of 74-81°F, 6-8 pH, and 5-20 KH.

You don’t need any special equipment to keep the water healthy, just a filter to clean it and a heater to maintain the ideal temperature range. Most aquarium lights are suitable too.

Attach equipment firmly to the tank or they will suffer at the hands (or fins) of an Oscar’s digging. Keep the lid on because these fish are powerful and may jump, or force other fish to jump.

While they like strong currents in the wild, the filter outlet should create a strong enough current, so you shouldn’t need a water/air pump.

What Size Aquarium Do Oscars Need?

Oscars will need a fairly large aquarium, 55 gallons or larger is ideal. A smaller tank will cause them stress which will make them ill or more aggressive.

How Many Can Be Kept Per Gallon?

Their size and need for territory means each fish needs lots of space. Try 55 gallons for the first Oscar, then 20-30 gallons more for each additional fish.

Oscar Tank Mates

Red Oscar

This species is not the best at making friends. Their aggressive nature can cause tank mates to live in fear (assuming that they haven’t already been eaten).

In South America they live in some of the most diverse areas of the world, so they are used to lots of other fish.

However, this is not the same in a tank because there’s much less room, so tensions rise. An Oscar only tank is probably the best idea if you want these cichlids.

If you are looking to turn your tank into a community then you’ll need to choose some large, passive fish that will stay out of the way while also being able to defend themselves.

A few good examples include: Arowanas, Bichirs, Convict Cichlids, Firemouth Cichlids, Green Terrors, Jack Dempseys, Jaguar Cichlids, Sailfin Plecos, Severum Cichlids and Silver Dollars. As you can see, fellow cichlids are the most common tank mates since they can usually hold their own against an Oscar.

Any small fish you add will quickly disappear from the tank. This will be the same for small invertebrates like shrimp and snails too.

Keeping Oscars Together

Oscars can be kept together, and this is usually the safest option. Just make sure to follow the stocking guidelines mentioned above.

Their need for territory can cause them to attack tank mates. Make sure they have lots of space as this reduces territory disputes.

What To Feed Oscar Fish

Pair of Oscar Fish

Whilst it can be difficult to find suitable tank mates for Oscars, providing a healthy diet is not. They’re omnivores and will eat pretty much anything you give them.

In the wild they would eat small fish, larvae and small pieces of plant debris. Small insects and crustaceans would make up the largest part of their diet.

In an aquarium the simplest option is to use store bought flake/pellet foods. These have been designed to contain all the nutrition your fish need, you can even buy some specifically for cichlids.

Other options include live/frozen foods (which are full of protein). These include bloodworms, brine shrimp and daphnia. Live foods encourage Oscars to catch their food which brings out their natural hunting instincts.

If you have some spare green vegetables around your kitchen then you can chop them up and put them in the tank. Or you can use them to make your own homemade fish foods.

Though they might nibble at plants, this won’t be a large part of their diet if you’re feeding them enough of other foods.

The best diet will be a mixture of different food types to provide a range of nutrients which your fish will need to stay healthy.

Feed them a couple of times a day, in amounts that they can completely finish in a couple of minutes. Watch out for aggression as these cichlids get excited around food.

How To Care For Oscar Fish

Albino Oscar

Oscars require more care than most other species.

Their size and large appetite means that they produce a lot of mess.

This makes cleaning the tank very important, or conditions will deteriorate quickly. Perform water changes at least once a week, ideally twice.

These cichlids are hardier than most fish, so they don’t get sick often, but they can get ill just like all species.

A common problem for these fish is “hole in the head” disease. This is where cavities and holes begin to form.

This could be a sign that they’re not getting enough nutrients in their food. It is worth changing their diet if you see signs of this disease.

Breeding Guide

These are one of the hardest fish to breed in captivity.

Individuals are very picky when choosing a mate, so you can’t assume that putting any old male and female together will result in juveniles.

You can try to buy an already established breeding pair. Another option is to buy a group of juveniles, as they grow together they will build a connection and be more likely to form mating pairs.

A problem with the second option is that it will take a while for breeding to happen since you will need to wait until the juveniles have matured; this takes 1-2 years.

As long as the Oscars think they’ve found a suitable mate, you can breed any combination of individuals from different varieties.

Naturally these fish would breed in “rainy season”. To signal rainy season in an aquarium try lowering the temperature a couple of degrees. Water changes every couple of days along with sprinkling water on the surface for a few minutes each day will also help.

When the fish are ready to spawn they’ll flare their gill and use their fins to indicate to their mate. This could be simple fin waggling or vibrations.

The pair will clean a rock surface for the eggs to be laid on. The largest females can produce up to 3,000 opaque white eggs.

Both parents will guard the eggs until they hatch (after 2-3 days); females fan them to keep the substrate from smothering them, while males keep other fish away.

Move the juveniles to a new tank with a sponge filter for the best chance of survival. Feed them around 2-4 times a day to help them grow quickly. You will have to move them again as they get bigger or the tank will get too small and their growth will be stunted.

FAQs about Oscars

How Big Do Oscar Fish Get?

They grow very quickly; up to one inch per month until they reach around 12 inches in length. In the wild they usually grow slightly larger and there have been reports of these fish growing up to 18 inches.

What Do Oscar Fish Eat?

They are omnivorous so they’ll eat a wide variety of foods. In the wild, they mostly live off a diet of small insects and crustaceans, supplemented by some live fish and dead plant matter.

You can feed them a pellet or flake diet, with the occasional live food treat.

How Long Do Oscars Live?

Most live between 8-12 years, however given the right care, tank conditions and diet, they can live up to 15 years.

What Is Hole in the Head Oscar?

Hole in the head disease is a common freshwater fish disease which commonly affects large cichlids such as Oscars and Discus. Also known as Hexamita, symptoms include white stringy feces, faded color and loss of appetite.

Sometimes, but not always, this disease leads to lesions on the head and the body of the fish. This disease is caused by the parasite ‘Hexamita’ and can be fatal if not caught early enough.

Are They Suitable for your Aquarium? (Summary)

It’s rare that Oscars can just be added to an already existing tank since they need a carefully planned setup and specific tank mates. This cichlid is usually a centerpiece that you design the rest of the tank around.

This may sound like a lot of work, but your effort will be rewarded with some bright colors and unique social behaviors.

Once the tank is up and running you shouldn’t experience many problems. Diseases are uncommon and you have lots of choices with their diet. Breeding them may be a challenge but it’s not impossible.

If given the chance, Oscar fish will quickly work their way to become one of your favorite fish.

Do you keep Oscars with other species? If so, which ones? Let us know about your setups in the comments section below…

Robert Woods Portrait
Robert Woods is the creator of FishKeeping World, a third generation fish keeper and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America and the Nature Conservancy.

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