Oscar fish: how to keep and breed this aggressive fish

Oscar fish or oscar cichlid (lat. Astronotus ocellatus) is a large and bright colored freshwater cichlid from South America. This is one of the most renowned aquarium fishes of Cichlidae family. It is a large, aggressive, but very smart fish. The article tells about how to keep it, feed, choose its tank mates, breed it.

Habitat in the wild

The kind was described by Louis Agassiz in 1831 and received the Latin name Lobotes ocellatus. Later it was renamed Astronotus ocellatus. The generic name originated from the Greek words astra (a ray) and noton (a back), which indicated the shape of its dorsal and anal fins. The specific name ‘ocellatus’ translated from Greek, means oculated and indicates the fish’s peculiar black spot at its tail’s base that resembles a large eye.

The fish can be found in South America: in the east of Venezuela, Guiana, the Amazon basin, the rivers: Rio Negro, Paraná, Paraguay. In the wild, they are often encountered in the forest slow-flowing or lentic habitats with a muddy bottom, where the fish keeps close to roots of flooded trees under the shelter of emergent plants. It feeds on fish, crawfish, worms, and insects.

Oscar fish was accidentally taken to China, Australia, Florida, where it acclimated rather quickly and started hunting local fish species to extinction. In its native habitat is considered a valuable food fish.

It first got to Europe in 1937 and became popular among aquarists due to its bright coloring, large size, and peculiarities of its behavior. It quickly gets used to its owner, starts to recognize him, and even lets him touch it.


Fish has a strong oval-shaped body with a big head and large thick lips. In the wild, oscar’s max size can be about 45 cm (18 in) and 1.6 kilograms (3.5 lb) in weight, but in a tank, the fish is smaller – about 30 cm (12 in). It reaches its maximum size at the age of 3-4 years.

Provided with good care, oscar fish lifespan can be about 12 years and more.

It has a large pointed head with an arched forehead. It has fleshy lips and a large mouth with small teeth in it. All these characters depict a typical predator.

Species that 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 the fluke. Both wild species and those bred by humans change their color rather fast when stressed, during fights, or protecting their territory.

It is interesting that the juvenile’s coloring significantly differs from that of the adult species. Their spots are white, not red-orange. These contrast colors look very appealing.

Nowadays, several selective breeds were obtained with different coloring and body shapes. It is almost impossible to name all oscar types since new species appear day after day. However, the most popular are the following:

Wild oscar fish

The natural color of the wild species is bright-yellow, gray, pale-green with bright stripes and some orange color inclusions.

Tiger oscar fish

It has non-uniform coloring. The general background may vary from brownish-grey to black with yellow spots and splotches scattered over the body, quite ofter each spot has black edges. At the beginning of the tail fin, there is a large black spot with orange edges that resembles a large eye.

Red oscar fish

This is a selective breed. Unlike its initial breed, this one has uniform red-orange body coloring without spots, lines, or curves. The typical dark spot at the beginning of the tail fin is missing as well. This species was obtained by a Thai aquarist Charoen Pattabonge, who noticed this unusual mutation and fixed its feature in further generations. Red Oscar doesn’t have a spot at the base of the tail that is peculiar to wild species

Fire red oscar fish

This variation includes species with bright, completely red body coloring.

Golden oscar fish

These species are similar to red Oscar. However, instead of red and orange tints, yellow and golden ones prevail.

Albino oscar fish

Albino species have a white body with bright orange or red spots. Their hey feature is pink or, more seldom, orange eyes and fins without any dark pigments. Otherwise, these are lutino species. The fins have no sign of dark colors. Tank conditions for them don’t differ from the ones for other Oscar kinds.

Lutino oscar fish

They look like albino species, but their coloring is darker, mainly it is their fins and the spot on the tail. If you got an oscar with dark eyes and fins that looks like albino, this is lutino. The thing is that albinos can’t produce color, brown, and green pigments.

Blueberry oscar fish

Species that belong to this variation initially appeared as albino or lutino, but they were dyed with a blue dye.

Lemon oscar fish

This is one of the most popular kinds, but it’s extremely hard to find on sale. The fish has a bright lemon-orange coloring all over its body.

Veil Tail oscar fish

This variation has elongated fins and also can have various types of body coloring.

Difficulties in keeping and oscar fish as pets

Although it is an interesting fish and easy to be taken care of, it’s important not to judge it by its size at the juvenile stage and its peaceful behavior. The majority of tiger oscar on sale is about 1 inch (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 buy this fish to keep in your community tank of 100 liters capacity.

Cichlid grows very fast, and for right growth, it needs a tank of 400 liters capacity or more. Also, the feed for this fish is rather expensive. Besides, it is a raptorial feeder that should be kept in a separate tank with its couple match or a very large tank with large tank mates.

Oscar cichlid grows very fast, and at that, it eats all smaller fishes in a tank. Astronotus, just like all large and raptorial feeder cichlids, should be kept in a big tank. It’s preferable to keep this fish alone without any 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 fish.

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

Besides its large size and attractive color, Astronotus is also considered a very clever fish with interesting behavior. This fish is rather small at the juvenile stage, but it grows fast to reach max size (up to 45 cm), and of course, it attracts any aquarist’s attention. It is one of the fishes described as a fish with some kind of intellect and temper.

Cichlid will watch you doing your business in the room, and you’ll see that it does it more consciously than other small cichlids. Some fishes even let you touch them, like a pet cat, and it looks as if the fish is enjoying it. Taking food from hands isn’t a problem at all for tiger oscar, but be careful – it may bite you.

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

Care and keeping in a tank

Scientific NameAstronotus ocellatus
Common NameOscar, oscar fish, tiger oscar, velvet cichlid, marble cichlid
Ease of keepingEasy
Lifespan12 years and more
Tank size500 liters (110 gal) or more
TemperamentTerritorial and aggressive
Tank typeCommunity of large fishes
Temperature23 and 28 °C (73,4-82,4 °F)
Water hardness9–20 dGH
Sizeup to 45 cm (18 in)

Selecting and buying

If you have a serious intention to keep or maybe even breed oscars, you should get not less than 4-8 species. Since the sex of even a mature fish almost can’t be defined, it’s recommended to buy a group of 4-8 juveniles to keep them in a tank and to let them choose their match themselves. The best-matched fish couple is left in a tank, and the others are transferred to other tanks.

It’s better to get juveniles about 2 inches (5-6 cm) large. Getting smaller-sized ones increases the chances of them being ill, etc., and they have fewer chances of successful adaptation in the tank. Don’t select fish of the same size since they may be all of the same sex.

Pay attention to the fish body build. They shouldn’t have retracted abdomen, roached back, or bulging eyes. When getting selective species, make a point of their head and jaws shape since these are more likely to have some imperfections.

New-bought fish should have some quarantine period. Usually, it’s not less than two months.

Tank size

This is a very large fish, and it has to have a tank of an appropriate size. Fis juveniles will feel rather comfortable in a tank of 100 liters (22 gals) capacity, but when they grow up, they’ll require 500 liters (110 gals) or more. If you plan to have this fish couple for breeding much larger tank is required to lessen the number of fights between the fishes. To keep a small oscars group, you’ll need even a larger tank, but keeping them in groups is not recommended.

Water parameters

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

The fish is a thermophilic one. The recommended temperature range is from 23 and 28 °C (73,4-82,4 °F). Variations are possible, but only to higher values. Water temperature less than 20 °C (68 °F), is extremely undesirable, while 13 °C (55,4 °F) is a threshold below which the fish die.

To maintain optimal water temperature, you’ll need a heater with a thermostat. It’ll be better if a canister filter is intended for installing a heater, i.e., the water will be heated outside the tank since some species may attack the heater and break it as a result.

Oscars are not demanding in terms of the water parameters; they feel good both in slightly acidic and alkaline mediums. The optimal pH range is from 6.0 to 7.5, and lower acidity values are not desirable since, in the wild, the fish isn’t encountered in black waters.

Water hardness may vary from 5 to 20°GH.

The fish is quite tolerant towards low oxygen content in the water, and they can survive even at concentration 0,4 mg/l.

Tank setup: decorations and plants

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, etc. The good thing is to hide heaters with big rocks or other tank decorations.

Oscar fish may start playing with decorations by attacking them, so due to the fish size, it may end up rather sadly for the decorations. If your fishes 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 fish 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.

To keep oscars, a tank without substrate will do since it is easier to keep it clean. If you need a substrate, we recommend using large-sized gravels. Large stones are put on the tank bottom. Using snags or tree branches as decorations will make the tank look more like the fish’s natural habitat.

If you want to use wild plants as decorations, these should be stiff-leaved ones with a strong root system and planted in separate containers. It is better to use artificial plastic plants, though. The fish is poorly compatible with live plants. You may use stiff-leaved plant kinds (anubias) put into flower pots to prevent the fish from digging them out.

Other than that, tiger oscar is a 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 its side and pretend to be dead. It is rather smart. They get used to their owner rather quickly and take food from their hands, and sometimes they even let you touch them. If you intend to create some kind of scape in your tank to make everything look nice and perfect, please remember – oscar fish is the boss in the tank, not you. The fish will dig and remove everything they see in their own way.

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.


Selecting water filtering equipment is maybe the most important thing when equipping the tank for oscar fish.

Since they are quite large and prefer food with high protein content, each meal ends with essential water pollution both with food leftovers and their waste products.

Using a water filter not powerful enough leads to toxic components accumulation in the tank water that finally may cause many issues with the fish health.

The best choice is to use one or two external canister filters. At that, they should ensure the performance capacity of 7-8 tank volumes per hour. Besides, modern canister filters provide a proper level of biological water purification. Also, their maintenance is more convenient than that of internal filters.

To remove from tank water the nitrates that appeared due to biological filtration, you should renew water at about 30% of the total tank volume once a week.


The fish is omnivorous, and this is shown by the results of a study of the wild species stomach contents. They found small fishes remnants, crustaceans, insects, some parts of terrestrial and aquatic plants. In the wild, the cichlid is euryphagous, and it eats different food, including insects, larvas, zooplankton, plants and algae, fish, spineless species, etc.

The fish is rather easy to feed. However, it’s desirable to give it animal feed. The basic meal should be qualitative feed for large cichlids – granules, tablets. Live or frozen food can be some addition to the main diet of oscar cichlid.

The fish eagerly feeds on earthworms and sloughs and crickets, prawns, fish fillet, mussels meat, frog larvas, grasshoppers, and other large-sized food.

Such spread kind of live food as bloodworm can be used only in the diet of the juvenile. The adults require larger-sized live food such as earthworms, large insects (crickets, grasshoppers), etc. Before feeding the fish with earthworms, keep them in a volume with water for 3-4 days to clean them from the soil.

The vast majority of aquarists feed oscar with a fillet of sea-fish, calamari, and prawns, pieces of raw beef, heart, and livers. They cook these or freeze forced meat.

Surely, oscar cichlid is fed with eating fish (like goldfish), but it should be done only if you are sure that these fishes are healthy and won’t infect the fish you are feeding them with.

Cichlid 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 times when cichlids 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 the high content of proteins and fat in it. This leads to fatty degeneration and dystrophy of fish viscera. As for ox heart, it’s better to feed it to the fish once a week not to load the fish stomach.

You should better stick to quality dry food for cichlids. Their advantage is obvious – they are rich in high-quality proteins, completely balanced, contain necessary vitamins and minerals. At that, they are completely safe, easy to store and feed.

Such food is selected according to the fish size.

Adult oscar will fancy food in the shape of sticks. They float on the water and, due to their shape, resemble the food shape the fish eats in the wild. At that, it completely meets large-sized fish appetite requirements in protein content.

To amplify the spots coloring on the fish body, you can use the food Colour containing a concentrate of natural color boosters.

For small-sized oscars, we can recommend small granules or flakes made for all cichlid kinds.

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. Still, when reaching 4 in (10-12 cm) length and becoming reproductive, the fish also becomes aggressive. It’s better to keep one couple in a tank since then or maybe several fishes together if the tank capacity allows doing so.

Oscars are relatively peaceful kind but when kept with fishes of similar size. Since they are carnivores by nature, any fish that fits their mouth size they treat as prey.

If a tank is spacious, you can keep oscar with other large fish kinds such silver arowana, black pacu, managuense cichlid, red terror cichlid, Texas cichlid, Jack Dempsey fish, flowerhorn and other large cichlids, sailfin pleco, parrot fish. You shouldn’t keep them with angelfish, although they are from the same family. Oscar is too large and aggressive tank mate for angelfish.

Bristlenose plecos may be quite appropriate in a tank with oscars. It was noticed that if kept together, they grow larger than with other tank mates. There is no need to feed bristlenose plecos with some special food in this case since oscars eat messily and quite a lot of leftovers fall on the tank bottom.

Yet, it is better to have a species tank and keep just a couple of oscars in it.

Sex differences

It’s very difficult to see between males and females. You can define who is who for sure only during their spawning period because females have an ovipositor. Breeders usually buy about dozen of juveniles and grow them together to let the fishes choose their match themselves.


Since fish 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 consider that despite their size, it is rather timid fishes, and they react very fussily at any noise or movement near the tank with juveniles.

In the worst-case, all eggs and juveniles will be eaten. If there are some tank mates in the tank for the sake of juveniles and tank mates safety (oscar fish 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 for spawning (the best results were obtained when the tank size is 100x50x50 cm).

Big flat rock should be put on a tank bottom where the eggs will be put, and the substrate isn’t necessary. Water has to be not hard with neutral reaction; lighting doesn’t make a big difference, the water temperature must be raised to 28 °C (82,4 °F).

During the spawning period, the fish becomes very bright colored, the body becomes dark black, and the blotchiness becomes bright red. Sometimes the male isn’t very good to a female initially, but if the couple is separated with a glass wall for several days, the male will become more tolerant.

For a day or two, the fish couple thoroughly cleans the rock’s surface, 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 of 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, 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 fishes’ body. Juveniles try to stay closer to their parents, and they swim in small schools around them.

Fish juveniles grow fast but at a different rate, so they must be frequently sorted in a tank to prevent the larger fish juveniles from eating the smaller ones. Besides, a large number of fast-growing juveniles (they are up to 2 cm long) requires everyday 20% water renewal and a powerful filter in their tank.

The fish can spawn about 10 times in a 3-4 weeks interval. After this, they’ll need some rest for 2-3 months (sometimes longer).