Oscar Fish Care: Comprehensive Guide

Oscars are among the longest-running favorites for aquarists. Whether it’s an American Cichlid tank or just enjoying one of the best pets around, they’re available, cheap, and one of the most interesting fish that an aquarist can keep.

While they’re durable when it comes to water conditions, you still need to know a bit about their behavior for proper care. Let’s dive in and I’ll show you the ins and outs of keeping these incredible fish.

Oscar fish

Oscar Quick Care Sheet

  • Common Name: Oscar
  • Alternate Common Name(s): Tiger Oscar, Velvet Cichlid, Marbled Cichlid
  • Latin Name: Astronotus ocellatus
  • Care Level: Beginner to Intermediate
  • Tank Size: 55+ Gallons
  • Size: 12-16”
  • Diet: Carnivorous
  • Behavior: Aggressive and Intelligent
  • Lifespan: 20 Years
  • Reproduction Type: Egg Laying 
  • Water Temperature:74-81°F (23-27°C)
  • pH: 6.0-7.5
  • Water Hardness: 12dH – 15dH

Origins of the Oscar

The Oscar is a South American cichlid, originating from the Amazon and other large rivers with their tributaries in the area. They’re strong, powerful predators that will chomp on anything that fits in their mouths.

Oscars are a popular aquarium fish, owing to their beautiful appearance and aggression. That said, they’re often sold when small and cute which can be a huge problem if you don’t know what you’re getting into.

Oscars are my favorite fish of all of the freshwater options out there, but they’re not for everyone. All cichlids are relatively intelligent, but Oscars take it up a notch. Add in their size, territorial nature, and fearless aggression, and that cute little 3” fish you picked up at the LFS can seem like a monster in short order.

If you’re looking into keeping South American cichlids, then they’re a great place to start. The main reason is that Oscars communicate more effectively than most cichlids. Once you pick up on it they’re very easy to read.

It’s hard to call most fish “pets.”. Most will bop about their enclosures, and the most you can hope for is that they’ll recognize you feeding them. 

Oscars, especially when kept alone, become actual pets in short order. They’ll follow you around the room as best as possible and interact with you while you’re feeding them or working on the tank.

Oscars are tough fish and have been captive-bred for decades. This allows them to tolerate a wide variety of different water conditions without any issues. The waters they come from are soft and relatively acidic, an Amazon blackwater biotope is ideal to replicate their natural environment.

They’ll do just as well in a bare-bottomed 55-gallon with some rocks.

Most of the problems you’ll run into with Oscars are behavioral, rather than being related to their environment. If you can cycle a tank, you can keep a system suitable for an Oscar but managing aggression levels and understanding their behavior is the key to a happy fish.

Overall, the Oscar is a fine choice for anyone wanting an aquatic pet or looking into keeping South American cichlids. For most aquarists, the problems are going to be related to behavior rather than to difficulty in maintaining their environment.

Ideal Tank Setup

Oscars need just a few things to remain physically healthy. Any cycled tank of the right size will do, but let’s take a look into the dos-and-don’ts when it comes to keeping these fish.

Tank Sizing

Oscars take more tank than you’d think given their size. A 55-gallon is a good home for one Oscar and possibly a tough bottom-feeder like a large common Pleco. You’ll need at least 75-gallons to keep more than one.

There are two main reasons they need so much tank:

  1. Territory Claiming- Oscar will decide a portion of the tank is theirs and defend it relentlessly. They’ll even defend it from you, which is a rarity among fish in my experience. This naturally takes a lot of room.
  2. Dirty Eating- Oscar spread their food everywhere when they eat. They put out a ton of waste as well. Combine these two facts and you have a fish that punches above its weight when you’re looking at bioload in the aquarium.

Size is the most important factor for their tank, bar none. It takes precedence over the substrate, decorations, and anything else you might normally worry about with fish. Stick a few rocks on a bare bottom and an Oscar won’t mind. They’ll just claim part of the formation as their territory and that’s that.

Equipment

Normal equipment for the tank is fine, but I recommend running extra filtration. Oscars don’t mind a bit of extra flow, and it’ll help keep the water clean despite their waste output.

I usually pair a HOB with a good canister filter, both rated for the tank size. This can limit the other fish you put them in with, but the Oscar itself won’t mind. I’ve always paired mine with a common Pleco. They enjoy high flow rates and are almost impervious to the Oscar’s jaws.

Everything else just needs to be sized for the tank.

Decorating an Oscar Tank

Oscars like to move things around.

Any plant in the tank is a complete loss. I’ve successfully kept Anubias barteri with them, but the log had been seeded with a half-dozen plants and grown in for over a year in a planted tank before being added. The Oscar still attacked the plants relentlessly for a couple of weeks.

A substrate isn’t necessary for the fish and makes it harder to clean. But… not everyone likes to run bare tanks. Some kind of sand or very small gravel seems to work best, and the Oscar will occasionally scoop fallen food out of the sand and blow it through its gills while getting the morsel of food it was after.

Lightweight decorations won’t be in place for long. That includes small sticks of driftwood or plastic decorations that the Oscar can get its mouth on. They’re very strong and you’d be surprised at what they can actually move around if you’ve never kept one before.

Go for simple and heavy. Rocks and large pieces of driftwood do the trick, but anything movable will be moved around the tank.

Always Use Hooded Tanks

Always keep Oscar with a hooded tank. They’re excitable, can jump incredible distances, and some specimens seem to actually enjoy jumping out of the tank.

Their fins all have sharp spines on them and they’re incredibly powerful for their size. That’s not a fun combination when you’re trying to get them back into the tank after they took a leap of faith.

Just make sure your tank has some kind of covering.

Feeding Time

Feeding Oscar is pretty simple: just drop in something meaty like crickets or frozen bloodworms and they’ll devour it. For my part, I prefer to feed blood worms as the most common basis of the diet, with the occasional cricket or mealworm thrown in.

Pellets are also a great way to feed them. Oscars are never picky about food, and they’ll readily go after pellets. You can even make a game of it by tossing them around the tank and watching your fish chase them down.

The only problems come with feeding them when other fish are in the tank. An Oscar won’t hesitate to bully smaller fish and claim the lion’s share of the food. Adjust feedings accordingly, however, and everyone will do just fine.

Oscar Fish Behavior

Perhaps the most interesting part about Oscars is their incredibly intelligent behavior. This can be problematic for some people, especially those who don’t learn how to read the fish.

Fortunately, Oscar are rather expressive so understanding how they interact with you is much easier than it is with most fish.

Changing Colors

Many cichlids change color to express themselves. Oscars take it to the next level, with almost exaggerated expressions.

Oscar will brighten their orange and darken the black on their skin when excited or happy. When their skin is a dull grey with washed-out orange they’re unhappy, this may be accompanied by laying on the bottom of the tank.

Yes, your Oscar will sulk.

While there are minor variations, in general, you can start with the assumption that a brightly colored oscar with a deep, dark coloration is a happy one while an unhappy fish will be extremely pale.

It’s easy to confuse an upset Oscar for a sick fish or vice versa, so learning about this form of communication is essential to keeping them healthy.

Stimulation

As mentioned above, an unhappy Oscar will sulk. If they’re kept alone, Oscars need some form of stimulation or they get rather dull and inactive.

This isn’t a problem in a tank with other cichlids, where the fish’s territorial behavior and constant testing of other fish will keep it occupied.

When kept alone, however, you’re looking at a different situation. Oscar should be kept in a room that has people in it often, and at least the owner is going to need to learn to interact with the fish. Something as simple as trailing your finger along the front of the tank occasionally can help keep a bored Oscar from getting depressed.

Whoever regularly feeds the tank is going to become that Oscar’s person, and they’ll be more eager to interact with them than others. You’ll know they’re bonding with you when they begin to “dance” whenever you get near the tank. I hesitate to call it wagging their tail, but that’s what it looks like.

Oscar can also be taught tricks. I’ve taught them to swim through hoops, jump out of the water to take food from my hands, and a few other simple tricks. Food-based rewards will show you just how quickly these fish can learn. 

It helps them with boredom quite a bit as well

They’re not like a cat or dog that needs constant attention, but you should always acknowledge and interact with your Oscar when you’re in the room. Boredom will lead to the fish simply laying on its side with pale coloration for extended periods.

Managing Aggression and Territorial Behavior

Oscar bites hurt, but they rarely cause actual injuries. Broken skin is about the worst you’ll suffer from, even if you get chomped by a full-grown fish.

And you’re probably going to get bitten a few times. Especially if you need to clean in “their” portion of the tank. They may or may not stop after a while, depending on the individual fish. 

My favorite Oscar never lost his defensive behavior over his rock pile even after years of being with me. I just made sure my hand was in a fist when I needed to do something in his side of the tank, he’d give up after trying to bite my knuckles two or three times and I was free to clean as long as I didn’t move his rocks.

While they’re not a serious risk to humans, you do have to worry about other fish. Oscars are tougher than their size indicates, and they can hammer it out with notoriously aggressive cichlids like Green Terrors and Jack Dempsey all day. 

You cannot keep Oscar with similarly sized fish that aren’t similarly aggressive or armored. An Oscar will kill them sooner or later.

Managing the fish’s aggression with other species is a balancing act. It becomes intuitive after a while, but cichlids are all highly individual fish. That can mean unpleasant surprises if you’re not careful.

In general, you should watch for lip-locking behavior. 

If it’s occurring frequently with another cichlid then there’s a serious territorial dispute and one of the fish needs to be removed from the tank. While an impressive show of muscle it can lead to fatal disputes. Cichlids, Oscar included, will kill to defend their territory even if there’s no chance of eating the loser.

One thing I learned early on will help: you should move all of the rocks and other decorations around when adding a new cichlid. This disrupts existing territorial lines and allows the fish to form their own borders. It’s no guarantee against things going south, but it helps ease the initial aggression when a new fish comes into play.

Live Feeding

Oscars get a lot of joy out of the hunt, and in my experience, their behavior gets a bit less aggressive with regular live feedings.

That said, live feeding is dangerous if you’re not careful. That Ruby Red Minnow can carry any number of diseases, and feeders are often kept in worse conditions than other fish.

If you’re going to feed live fish, you need a separate quarantine tank and they should be in there with no additions for at least two weeks before feeding.

Stick with Ruby Red Minnows if you’re planning on regularly feeding fish. Goldfish have a surprisingly high-fat content and can be unhealthy if your Oscar (or other big cichlids) eats too many of them.

Suitable Tankmates

The actual list of suitable tankmates for an Oscar are pretty small:

  • American Cichlids- And only American cichlids. Africans will end up fighting endlessly with American cichlids, but when only fish from the same region are introduced they’ll usually stop fighting after establishing initial territories.
  • Armored Catfish- The Common Pleco is the only tank cleaner I’ll use with Oscars. Find one that’s bigger than the Oscar for the best results, and make sure it has a cave to hide in. Any Pleco that can fit in their mouth is going to end up as lunch.
  • Amazon “Monsters”- Uncommon, large predators like Arowana and Arapaiama are usually fine co-existing with Oscar, but if there’s a problem it’s going to be more difficult to fix things than when everyone involved is a cichlid.

Oscar will eat anything that fits in their mouth. Invertebrates are right out for the most part, including crayfish and freshwater crabs, and shrimp are just an expensive feeder when added to a tank with an Oscar.

It’s a short list, and I recommend keeping them either alone with a Pleco or only with other cichlids.

Breeding Oscar

Breeding Oscar is actually a bit of a problem for most people.

There are two big factors in that:

  • Oscars need to be 2-3 years old before they’re sexually mature, some even older. It requires a lot of space to keep a breeding pair and a lot of time for them to reach an appropriate age.
  • There’s no visual sexual dimorphism in this species. A female and male Oscar will both look identical. Their sexual organs are the only difference and aren’t observable until mating has begun, especially by an amateur aquarist.

So, a newbie breeder’s options are limited. You can either purchase a known breeding pair from a dealer, or you can keep 6-7 Oscar in groups and hope they pair off. That’s going to require at least a 125-gallon tank and months to years of time.

The male and female will be quite aggressive with each other during the courtship ritual. You’ll need to provide both with adequate hiding places so they can get relief from the other fish when necessary.

Breeding is usually triggered by a mixed, high-protein diet and warmer temperatures. Raising the temperature to the low 80s is good enough. Mixed foods are easy to handle with a visit to the pet store. Small mealworms, crickets, and frozen food varieties will make for a sufficiently varied diet.

You’ll also need to provide them with an area to lay the eggs. The eggs are adhesive, and the Oscars will often clean off a large, flat rock to lay them. Instead of that, you can provide them with an overturned ceramic plate, which usually gives them a great spot to lay their eggs.

The fry can be removed to another tank, which should be cycled and have good filtration and aeration, to hatch if you’d like. The parents will protect the eggs vigorously, no other fish should be in the tank.

They’ll take a few days to hatch, and a few more days to become free-swimming. Once they’re swimming, you can feed them baby brine shrimp. Make sure to keep water quality high, the fry are more vulnerable to bad water conditions than the parents.

Most of all, breeding Oscars is an exercise in patience. Even a paired set of fish can take months to years to successfully breed. Once the eggs have been laid, however, Oscars are remarkably simple to take care of.

Making Friends With the Oscar

Oscar fish care is simple, it’s managing their behavior that becomes the real challenge. With that said, these intelligent, active fish are a fast favorite among aquarists for good reason. Try keeping one, they’re an interactive experience rather than simply a visual one.

Making friends with an Oscar is a rewarding experience for both of you, it’s just going to take a little bit of time to learn how to communicate.