Oscar Care Guide


Oscar Care Guide

Large fish are often seen as the epitome of the hobby thanks to how impressive they look gliding about a spacious tank. Larger tanks may take more time to care for but they aren’t necessarily any more difficult. And Oscars are some of the more mild mannered and easy to care for large cichlids out there, giving you an easy introduction into the mega-fish world!

Characteristic Detail
Scientific Name Astronotus ocellatus
Adult Size 11-14 inches
Temperament Semi-aggressive; Territorial
Lifespan 15-20 Years
Care Level Beginner
Water Temperature 75-82℉
Appearance Chunky body with smaller scales. Typically red and chocolate brown; also cream and red (albino)
Water pH 5.5-7.5
Diet Carnivorous
Tank Size 55-75+ Gallons

Typical Oscar Behavior

Oscars get a bad rap as being “aggressive.” But as far as cichlids go they are fairly even tempered. Oscars have been in the aquarium hobby for decades – in fact they were some of the first truly large cichlids to become popular. So they certainly are more temperamental than the Guppies, Tiger Barbs, and other fish that were popular in earlier decades.

But Oscars are practically kittens compared to Red Terrors (Mesoheros festae), Umbees (Kronoheros umbriferum), and other truly vicious New World cichlids. A grumpy Oscar may decide to give short chase to tank mates, especially if the aquarium is too small or they refuse to back down.

Still, that’s pretty unusual. Generally speaking, Oscars are more likely to ignore their tank mates than harass them. All bets are off should you get a breeding pair, of course!

Oscar Appearance

Oscars are thick-bodied, even for cichlids. And their small scales have a fleshier appearance to them, giving them the second common name “Velvet Cichlid.” Nearly all Oscars have varying amounts of red; from an even spread of red and chocolate brown in Tiger Oscars to mostly red in the Red Oscar variety. There are also Albino Oscars, mixing cream and red.

Oscars also have slightly protruding eyes, which can be confusing for aquarists since Popeye is a common bacterial disease that mimics their appearance. An Oscar with Popeye will look positively grotesque, though. As long as an Oscar you’re considering has eyes that look like the others in the tank, you have little to worry about from Popeye.

Life Span

Larger aquarium fish tend to be longer lived but Oscars are extraordinary even for their size. 10 to 15 years is a typical lifespan for an adult Oscar, with up to 20 years being frequently reported. These are fish that you need to make a long-term commitment for.

Rehoming an Oscar that’s grown too large for you isn’t as easy as you might think; Oscars are some of the most common fish pet stores get calls for. Maybe overgrown Plecostomus are a little more common to find but not by much! And considering how fast they grow, you’ll be seeking a new home faster than you think if you buy an Oscar and aren’t prepared for their size.

How Big Do Oscars Grow?

11 to 14 inches is what you most commonly see in adult Oscars, with a couple inches in either direction depending on the diet and genetics of the fish in question. Keeping an Oscar in a smaller tank will not stunt its growth – it is an unfortunate myth that fish will grow only to the size of their tank. You may end up stunting its growth a little but that’s comparable to keeping a puppy in a box to ensure it stays small. An Oscar will grow as large as its genetics and diet dictate.

Sexing Oscars

Oscars are what we call monomorphic animals. This means that the two sexes look identical to us; there are no visual cues to go by when sexing the two. Males and females have similar coloration, size, temperament, and finnage. It’s likely that the fish use behavioral and hormonal cues that we can’t pick up on to tell each other’s sex. But it’s a lot harder for us aquarists!

The only clue you have is to look at the sexual organ, which is sometimes extended after a big meal, if the female is full of eggs, or both fish are eager to spawn. Males have a more pointed sexual organ while females will have a more rounded one. Oscars are sexually mature at around 5 inches in age.

Compatible Tank Mates for Oscars

As I said before, Oscars get a bad rap for being “aggressive,” when they are really more semi-aggressive and territorial in nature. All you really need to do is to choose tank mates fast enough to evacuate their chosen territory if your Oscar decides to turn mean.

Even if you want to make your Oscar the star attraction of your tank, adding a few dither fish will encourage him to remain active and eager. When fish are kept singly they often become shy because in nature, no fish swimming out in the open is a sign that predators are lurking. Cichlids are more confident in their aloneness than most. But I always recommend providing pets with a stimulating environment and tank mates are a great way to do so.

Choosing fish tough enough to hold their ground is also a good idea – but be careful when choosing other large cichlids because Oscars are on the milder side of the scale. Many same sized or larger species will end up bullying or even killing the Oscar outright in a fight. If you do end up wanting to set up a cichlid community tank then ensure the tank is no smaller than 75 gallons, with 125+ gallons being even better.

Good Tank Mates for Oscars Include:

  • Silver Dollars, large Barbs, and other Dither Fish
  • Larger Gouramis, medium sized to large Cichlids, Arowanas, and other Community Fish
  • Plecostomus, predatory Catfish, Stingrays, and other Bottom Dwellers

Water Conditions for Oscars


Being natives of the tropical Amazon basin, we want to provide Oscars with warm conditions. 75-82℉ is ideal for them. And increasing the temperature further to 84-86℉ can encourage them to spawn. It also boosts their metabolism enough to fight off troublesome diseases!

Water Chemistry

In the wild, Oscars are found in soft, acidic conditions where the water is relatively free of dissolved minerals and rich with humic acids from decaying plants and wood. But having been bred in aquariums for decades they are remarkably flexible, even thriving in alkaline conditions (pH 7.0+). That said, they are unlikely to breed unless you replicate acidic to neutral water chemistry for them (pH 5.5-7.0).

Tank Setup

Tank Size

Oscars are easy to keep in almost all respects. But providing them with enough living space can be a real challenge because they are not small fish. A 55 gallon tank is the absolute minimum for an adult Oscar but even that is too small in the long term. A 55 gallon tank is only 12 inches wide, which doesn’t give much space to a fish that’s 11 to 14 inches long as an adult. A 75 gallon tank is 18 inches wide, making it much more comfortable.

The extra water volume also ensures that the copious amounts of ammonia Oscars create won’t pollute the environment too quickly. Like all cichlids, canister filters are ideal since they process pollutants more efficiently than power filters do.

Feeding Your Oscar

What Should I Feed My Oscar?

Oscars are true carnivores, feeding on smaller fish, insects, shrimp, worms, and anything else they can catch and consume. However, you don’t need to feed them live food very often in the home aquarium. In fact, I recommend staying away from store-bought feeder fish.

Feeder fish are loaded with parasites like ich and are kept in filthy conditions where bacteria grow unchecked. Coupled with the poor quality feed they are offered, they are simply a reservoir of diseases for anything that eats them. Stick to a high quality carnivore pellet formula as your base for feeding an Oscar.

However, I do recommend supplementing your chosen formula with other live and frozen foods. Earthworms are a healthy favorite, though slightly rich in fat, so feed sparingly. Slices of store bought white fish, pieces of fresh shrimp, thawed mussels, and other seafood are also a healthy treat!

How Often Should I Feed My Oscar?

When young Oscars should be fed two to three times a day. But once they reach 8 to 10 inches in size their growth slows somewhat. At this point you only need to feed once or twice per day. Any excess food is just going to go towards fat in your fish and extra waste for your filter to process, so aim to feed a little less!


Breeding Your Oscar

How Can I Condition Oscars to Spawn?

The main challenge in spawning Oscars is our inability to tell the difference between the sexes. Since we can’t choose a pair from the pet store, the best way to spawn Oscars is to buy a small group and let them pair off naturally. Four to six youngsters will eventually figure out who likes who once they reach sexual maturity at 4 to 6 inches.

Though there is no guarantee they pair off right away; Oscars can be notoriously picky and it may take longer for a pair to emerge. But once you do end up with a pair, you should then rehome the others so the happy couple can focus on each other. Otherwise the breeding pair will harass their tank mates, often to death.

How Can I Tell if an Oscar is Pregnant?

Other than the female being swollen with eggs, the best clues are that the male and female will begin digging continually, searching for a hard surface to spawn. They will also ramp up their aggression dramatically, attacking anything that intrudes in their spawning area. Like most cichlids, Oscars are devoted parents and provide care to both their eggs and their fry for a few weeks!

Frequently Asked Questions

How Aggressive are Oscars?
Oscars are more temperamental than most community fish. But as far as large cichlids go they are mild mannered.

Can I Keep Oscars with Plants?

Unfortunately, Oscars love to dig, like most cichlids. Most plants will be plucked from the substrate and possibly torn up by them.

Will Oscars Eat Their Tank Mates?

Oscars are large predators. Any fish they can fit in their mouths may become a meal for one.


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