Oscar fish - Guide on care, breeding, tankmates

Special thanks to Abel Guerrero for his picture.

Basic information about the Oscar fish species:

Maximum size (min-max): 30.0 - 40.0 cm ( 11.8 - 15.7 in)
Recommended temperature: 24.0°C - 30.0°C ( 75.2°F - 86.0°F)
Recommended water hardness (dGH): dGH 4.0 - 18.0 N
Recommended pH of water: 6.5 - 7.5
Origin: South America

Introduction to the Oscar fish

This fish is very intelligent, it can even recognize it’s owner. Oscars have they own ideas, although they're not the only fish having them. If Oscars don´t like how the items are placed in the aquarium, they pick them up and replace them, or they spit it out from the tank. It doesn’t matter if the plant or rock is real or plastic. If you have a high aquarium, standing near it can be dangerous. The best choice is to have a sand bottom and a few big rocks in the tank. Sometimes Oscars pretend that they are dead. In nature they pretend to be dead and wait until a small fish comes close so it can be caught and eaten.


Oscars may be aggressive fish so they need a big aquarium and should be kept in a large group, because if there are only a few specimens in the tank, they will fight, and the weaker Oscar will feel miserable. The best solution is to have either one or many (6 is the minimum) Oscar fish, but never only a few. I have heard that sometimes three fish get along well, but usually they fight and attack each other without apparent reason. However, even if you have more of them in one tank, when they grow up a male and female may separate from the group and start to defend a part of the tank, in which case it is better to remove them. Understanding their behaviour is also important to avoid diseases as diseases are mainly caused by stress. Put two Oscars into a 100 liter (26 US gallons, 22 UK gallons) fish tank is like asking for a problem; not only they'll likely fight, but also they will feel uncomfortable and diseases are just a matter of time.

Oscar fish pictures

Information about care

In general, any Oscar fish grows very fast. As fry they do not need much space, but as they grow they need more and more space. The aquarium for one Oscar fish should be at least 200 liters large (52 US or 44 UK gallons), although once adult size is reached, the fish will hardly move in such a tank, so 400 liters is much more suitable. So if you want to have a happy fish with happy friends, you really need a very large aquarium. I would recommend having an Oscar aquarium only in large spaces like big restaurants, or you can keep them in garden aquariums, but not in an ordinary room. And, just like in all tanks it is important to have a filter, gravel, and a heater. The optimum temperature is between 26-28 °C (78-82°F).

The tankmates

The best tankmates for Oscars are Large Plecostomus and other large Neotropical Cichlids such as Texas Cichlids, Jack Dempseys, Salvini, and other cichlids from South America which are the same size or bigger. From the Oscar species the less aggressive are Pink Tiger Oscars. That is the reason why Red Oscars and Tiger Red Oscars can make Pink Tiger Oscars miserable. You should ensure that the Pink ones get their food too. Choosing tankmates is very important as plenty of people end up with Oscars only even though they've planned a community aquarium; The Oscar fish will simply eat small species.

In nature Oscars eat small fish. But in aquariums small fish can introduce diseases. Use live food wisely and try to keep the Oscars healthy by using vegetable based food with vitamins. I had success with my own grown feeder fish when raising Oscars - feeder fish were 100% healthy and Oscars thrived.

Breeding the Oscar fish

Breeding isn’t very difficult if you keep a pair. Perhaps it's repetitive, however I’d like to emphasize the importance of high water quality. Clean water is required, as well as a stable temperature of about 28°C (82°F). Don’t try to breed them in cold water, or water of poor quality! If you keep them in the same tank prior to a breeding program they will probably need some motivation, so remove a male for one or two weeks. Breeding goes well when you use live food and when you add oak wood to the tank. Use heavy rocks, they will clean them in order to lay eggs on. Large driftwood could help this process too. Generally, they breed like all large South American cichlids.

Thanks to Tamri Shavi!
Feel free to visit Oscar Care Basics at firsttankguide.net too!

Additional questions and answers

Since we merged aqua-fish.net/answers with articles, here below are questions that often fishkeepers ask. Some of the listed questions may have been partially answered in the article below, however listing them "as is" makes all questions easier to read! You're welcome to post your questions too, just ensure that they're unique - use a form at the bottom of this page for this purpose.

What is the smallest tank for an Oscar?
Answer: 300 litres (nearly 80 US Gallons). This fish can grow to 30-40 cm in length very easily.
What is the difference between an Oscar fish and a Jack dempsey?
Answer: The Oscar (Astronotus ocellatus) is peaceful, the Jack Dempsey (Cichlasoma octofasciatum) is not. Oscars come from South America, Jacks come from Central America.
Which other fish can live with an Oscar fish?
Answer: Peaceful species which are of similar sizes. Of course, you should choose these which come from South America due to similar demands on water and biotope. Never add smaller fish with an Oscar, they are normally kept with other large cichlids like the Pacu; adult plecostomus are fine with Oscars as well.
Why do my Oscar fish fight?
Answer: Oscars, like most cichlids are territorial fish, and if they haven’t been introduced into the tank at the same time will fight to claim their own piece of the aquarium.
What toys can I give to my Oscar?
Answer: A lot of keepers do not realize how intelligent Oscars are, adding a “toy” can keep them occupied to prevent sulking. I have used pieces of bogwood and even a cheap plastic plant that is not secured.
What size is the biggest Oscar fish?
Answer: Oscars can grow up to 16 inches in length, weighing up to 3.5 pounds. Always provide them with a large enough tank to grow out.
When are Oscars mature enough to lay eggs?
Answer: Several keepers claim that Oscars become mature at 12 months but it is more accepted that they mature at 16-18 months old.

source : aqua-fish