Oscar fish: how to keep and breed this aggressive fish

Oscars (lat. Astronotus ocellatus) is a large and bright colored cichlid from South America. Besides its large size and attractive color, oscars is also considered to be a very clever fish with interesting behavior. This fish is rather small at juvenile stage, but it grows fast to reach max size (up to 35 cm) and of course it attracts attention of any aquarist. Astronotus is one of the fishes which can be described as the fish with some kind of intellect and a character.

Fish will watch you doing your business in the room and you’ll see that it does it more consciously then other small cichlids.


Some fishes even let you touch them, like a pet cat, and it looks like if the fish is enjoying it. Taking food from hands isn’t a problem at all for oscars, but be careful – it may bite you.

Although wildlife species is still popular and widely available, but lately there have been bred quite a lot of new types of amazing colors which are popular, too.

All of them are beautiful, but red is especially attractive – it’s an fish with dark colored body with red or orange spots on it. Apart from red there are also albino oscar (completely white colored or with red spots), blue, and so on.

But all these morphs at bottom are yet classical Astronotus ocellatus. They are alike in keeping and feeding, except for some types that are more demanding and tend to get sick.

Luckily for aquarists, care is rather easy and it can be successfully kept in a tank even by beginners. Its size is the only thing that makes them troublesome when keeping in a tank.

They are grows very fast and at that it eats all smaller fishes in a tank. Astronotus just like all large and omnivore cichlids should be kept in a tank of 100 gal capacity and more.

It’s preferable to keep this fish alone without any tank mates.

Habitat in the wild

Astronotus was first described in 1831. The fish can be found in South America: Amazon River basin, the Rio Negro, the Parana River and the Rio Paraguay.

Oscar was accidentally taken to China, Australia, Florida where it acclimated rather quickly and started hunting local species to extinction.

In its native habitat its cichlid is considered as a valuable food fish. In the wild fish lives both in large rivers, channels, ponds, lakes with sandy or muddy bottom. It feeds on fish, crawfish, worms and insects.



Oscar has a strong oval shaped body with bid head and thick large lips. In the wild max size can be about 45 cm (18 in), but in a tank the fish is smaller – about 20-25 cm (10-12 in).

Provided with good care lifespan can be about 10 years and more.

Species which live in the wild are usually rather moderately dark colored with orange spots on their back and gills.

There is a big black spot with orange edges on fluke. Due to this spot the fish was called Astronotus ocellatus.

Both wild species and those that were bred by human change their color rather fast when they are stressed, during fights or when protecting their territory.

Difficulties in keeping

Although oscar is an interesting fish and easy to be taken care of, it’s important not to judge it by its size at juvenile stage and its peaceful behavior.

The majority of fishes on sale are about 3 cm long and at this period of time it’s kept in a community rank together with other fishes.

So, be careful not to by this fish to keep in your community tank of 20 gallons capacity. Oscars grows very fast and for right growth it needs a tank of 100 gallons capacity or more, also the feed for this fish is rather expensive.

In addition, oscar is a raptorial feeder that should be kept in a separate tank with its couple match or in a very large tank with large tank mates.

However, don’t get upset. If you are positive that this is the fish you want – go ahead – the fish is easy in care and soon you’ll have a nice, smart and almost pet.


Care and keeping in a tank

Scientific NameAstronotus ocellatus
Common NameOscar, oscar fish, tiger oscar, velvet cichlid, marble cichlid
Tank size100 gallons (400L) and more
Water temp75–81 °F (24–27 °C)
Size45 cm (18 in)

It’s a very large fish and it has to have a tank of an appropriate size. Due to the fact that even mature fish sex almost can be defined it’s recommended to buy a group of 4-6 juveniles to keep them in a tank and to let them choose their match themselves.

The best matched couple is left in a tank and the others are transferred to other tanks. Juveniles will feel themselves rather comfortable in a tank of 30 gal capacity, but when they grow up they’ll require 100 gallons or more tank.

If you are planning to have this couple for breeding much more larger tank is required to lessen the number of fights between the fishes.

Oscar prefers water with high oxygen content, but it doesn’t like water flow presence, therefore it’s required either to use aeration or to feed the water from an external filter through the pipe located above the water surface.

Since the fish is very large and rather active make sure that the equipment and tank design elements are installed reliably or it’s even better for them to have some protective cover or etc.

The good thing is to hide heaters with big rocks or other tank decorations. Fish may start playing with decorations by attacking them, so due to the size it may end up rather sadly for the decorations.

If your oscar tend to behave so, you can fool them by putting in a tank some object that will distract them from the tank equipment.

The bottom should be sandy since the fish likes digging it. In general oscar adores changing the tank interior as it likes – it digs, turns over, pulls out and throws things. So all rocks and snags have to be rather bulky and heavy and artificial plants should be anchored with something heavy to the bottom.

Other than that oscar is rather peaceful and slow fish, timid enough that even a lift net put into the tank can make it hide in tank corners or even lay down on a side.

The fish is rather smart, they get used to their owner rather quickly and take food from hands, sometimes they even let you touch them.

In case if you are intended to create some kind of scape in your tank to make everything look nice and perfect, please remember – fish is the boss in the tank, not you. The fish will dig and remove everything that they see right.

It’s highly recommended to cover the tank, so you’ll avoid splashes when feeding the fish and it won’t jump out of the tank.


In the wild the oscar is euryphagous and it eats different food including: insects, larvas, zooplancton, plants and algae, fish, spineless species etc.

The fish is rather simple fed, however it’s desirable to give it animal feed. Basic meal should be qualitative feed for large cichlids – pelleted foods.

Live or frozen feed can be some addition to the main diet. As for me, I use several different types of food, and change them from time to time.

The fish eagerly feeds on earth worms and sloughs as well as crickets, prawns, fillet, mussels meat, frog larva’s, grasshoppers and other large sized feed.

Surely, oscar is fed with eating fish, for example, guppies or goldfishes, but it should be done only if you are sure that these fishes are healthy and they won’t infect the fish you are feeding them with.

Oscar is very mean and they have insatiable avarice, so it’s important not to overfeed them, since it may cause illnesses and even death.

There were the times when cichlid were fed with mammals meat, but nowadays it’s better to avoid this.

The thing is that such meat can’t be digested well by the fish due to high content of proteins and fat in it. This leads to fatty degeneration and dystrophy of viscera’s.

As for ox heart it’s better to feed it to the fish once a week not to load the stomach.

I myself give some of this food to my pets and as for the rest I’ve heard and read lots of good reviews.

Yet, all of the food is of high quality and it is the best one for this kind as well as it keeps the tank water clean.

Compatibility and tank mates

This is absolutely not the fish for community tanks (whatever the seller says). While the fish is young it behaves rather well with other tank mates, but when reaching 10-12 cm (4-5 in) length and becoming reproductive the fish also becomes aggressive and it’s better to keep one couple in a tank since then or maybe several fishes together if the tank capacity allows to do so.

Tankmates may be only large or especially spiny fishes – jaguar cichlid, green terror, Jack Dempsey cichlid and other cichlids, large armored sailfin pleco and common pleco. All fishes except these will be eaten or at least bitten by fish.


It’s very difficult to see between male and female. You can define who is who for sure only during their spawning period by the fact that female has an ovipositor.

Breeders usually buy about dozen of juveniles and grow them together to let the fishes choose their match themselves.


Since the time when oscar becomes reproductive the couple occasionally spawns in the tank. Considering that they are the only fishes in the tank it’s possible to grow the eggs without creating a spawning pond on purpose.

You have to take into account that despite their size oscar is rather timid and they react very fussy at any noise or movement near the tank with juveniles. In the worst case all eggs and juveniles will be eaten.

In case that there are some tank mates in the tank for the sake of juveniles and tank mates safety (oscar in rage may easily kill or hurt even rather large fish if he’s sure that it threatens his juveniles) it’s better to have a separate tank of about 30 gallons capacity and more for spawning (the best results were obtained when the tank size is 100x50x50cm).

Big flat rock should be put on a tank bottom where the eggs will be put, substrate isn’t necessary. Water has to be not hard with neutral reaction, lighting doesn’t make a big difference, the water temperature has to be raised up to 26-28 °C.

During the spawning period the fish becomes very bright colored, the body becomes dark black and the blotchiness become bright red.

Sometimes male isn’t very good to a female at the beginning, but if the couple is separated with a glass wall for several days the male will become more tolerate to the female.

For a day or two the couple thoroughly cleans the surface of the rock and then they start spawning. Female lays the eggs in rows on the rock during 4-5 hours. The eggs are large and oval. Their number may be about 1000 and more, since the fish isn’t just big, it’s also rather fruitful.

Both parents take care for the eggs – they wave them with their fins, remove ruined eggs and guard ich fry. In 6-7 days ich fry turns into juveniles and they start to swim and feed.

Juveniles start feed can be brine shrimp, cyclops, as the fish grows it can be fed with cut tubifex.

Besides fish-parents during the first days have some nutritious secreta on their body and the juveniles eat it from the grown up body. Juveniles try to stay closer to their parents and they swim in small schools around them.

Astronotus juveniles grow fast but with a different rate, so they must be frequently sorted in a tank to prevent the larger juveniles from eating the smaller ones.

Besides a big number of fast growing juveniles (they are up to 2 cm long) requires everyday 20% water renew and a powerful filter in their tank.