Keeping Oscars: The Big, Beautiful, Bruising Brutes

Oscars; they’re big, brutish, beautiful, playful, inquisitive, aggressive, messy, intelligent, destructive, and personable. Is it possible so many words can describe a single fish? Anyone who’s ever kept one will say – almost unanimously – “Yes!”. And if you want to see what I mean, walk into any store with an adult oscar and see how it reacts to you.

Oscars are considered one of the most intelligent fish you can keep in your home, and I’ve certainly found this to be the case time and time again. Like most intelligent animals, they come with pronounced personalities that can border on human-like and there’s certainly no two that are the same. Some will certainly lunge at you, mouth agape, while others will follow you up and down the tank quietly and inquisitively observing you as you observe it. Some will push around the 2-foot-long armored tanks that are plecos, while others will sit quietly alongside diminutively sized pea puffer without a bother (although I would never recommend this.)

Many oscars, if kept by themselves, can become visibly depressed, bored, or frustrated if their owner doesn’t pay enough attention to them (which entirely depends on what their preferred level of attention is.) With that said, many report that oscars will demolish much larger tank mates, eat spiny catfish, and terrorize other oscars to death. Oscars kept in small tanks with few opportunities for enrichment like other fish, things to explore, plants to shred, or things to move, can also become bored, depressed, or frustrated.

Which brings up another point – they’re certainly opinionated fish! They have thoughts about just about everything you stick in the aquarium. If they don’t like where you place a heater, rock, filter output, plant – or any other thing for that matter – they’ll let you know by promptly moving it to a more suitable place or simply destroying it (this includes fish as well.) Many a’oscar have been killed by smashing heaters, breaking the glass by industriously rearranging rocks to their liking, or draining the aquarium of water by moving the filter output to outside of the tank – although there are surely more ways an oscar can bring on its demise. They can go on hunger strikes, display aggression towards strangers by lunging out of the tank (though rare,) and some can request your audience by bashing about the tank with wanton abandon only to stop once you acknowledge them.

They’re notoriously messy beasts too, often chewing, spewing, rechewing, respewing, and continuing until they’ve eaten about 25% of the food they initially took in with the remaining 75% spattered around the tank. (Or that’s my best estimate, anyway.) They’re also large – reaching up to 18” – although more likely reaching 16” or less, so a lot of food goes in and comes out. Somewhat ironically, they’re not tolerant of poor water quality and even with good practices can often develop hole-in-the-head (or HITH,) which is a blight nearly all oscars experience at some point in their life.

All these things make keeping an oscar more difficult than the average fish, and plenty of thought needs to go into the level of commitment you can reasonably handle for, say, the next 20 years? There’s a reason oscars are one of the most commonly rehomed fish on the market – they’re just too much for most people. But if you’re willing to put in the work, you’ll be rewarded with loads of personality, fun, frustration, and something that can only be described as friendship for years to come.

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Table of contents

Why does my oscar jump?

Many oscars have leapt to their demise and, unless you were around to witness what happened before he partook in the ultimate trust fall, all we can do is speculate. Oscars obviously come from large bodies of water where, if they spot food, they can leap out of the water to catch it and safely land back in water. The same is true for avoiding predation or same-species aggression, you didn’t think oscars were – literally – the biggest fish in the pond, did you? Similarly, if conditions are unfavorable in their current home, it would make sense to try to jump to another location, right? Or that’s currently our thinking on oscar logic. So, it’s important to keep the tank lid secured with clips or weight – like a very large rock or some weights.

Do oscars bite people?

Sure, they’re capable of doing so and statistics tell us if something is possible it will, eventually, happen. I haven’t heard many reports of this though. I’d assume this is for a few reasons, the first being if an oscar were to try to aggressively bite you, say you stuck your hand in while they had fry, most people would be smart enough to see the aggression for what it is and avoid the situation before it happened. Second, most people who hand feed oscars know how to place their hand in the water to avoid a finger in their mouth. Third, and probably most importantly, oscars don’t have jaws made for biting, they use suction to slurp up their prey. Their outer teeth that we see are small and sandpapery in nature, mostly for keeping grip on slippery scales. You’d likely be scuffed but unharmed. Their true chomping teeth are in their pharyngeal jaws (modified teeth located in their “throat”.)

What species of oscars are there?

A. ocellatus and A. crassipinnis are both available for sale under the common “oscar” moniker, but A. ocellatus are certainly more common. It’s been speculated they’ve been hybridized at some point in the line. Oscars are, however, not a well-researched lot and there’s speculation that other variants or species could be present that are currently misrepresented under those names. Fortunately, they both (or all) seem to have the same requirements. A. ocellatus tends to grow larger (up to 18”,) while A. crassinpinnis stays about half that size (9.5”).

Distribution & Natural Habitat

Oscars are found in slow-moving waterways, usually in forested areas, where they prefer silt-laden areas with marginal vegetation and root systems. They have a wide range of distribution in the wild and have been recorded in Colombia, Venezuela, Bolivia, Ecuador, Peru, Brazil, French Guiana, Paraguay, Uruguay, and Argentina. They have been collected from numerous river systems, including the Ucayali, Solimões, Amazonas, Negro, Madeira, Tapajós, Tocantins, Orinoco, Approuague, and Oyapock. Feral populations also exist in several countries, including Singapore and the USA.

In fact, oscars are an invasive species in the fragile and protected Florida everglades. No doubt these fish (or their ancestors) were dumped by people who could no longer house them, and when pet stores wouldn’t accept them likely felt they had no other option. Dumping any pet in the wild – fish or otherwise – is never good option. It potentially endangers hundreds of species and habitats and certainly can endanger the animal itself.

Oscars are successful in the Amazons because of their large size, massive brood sizes, parental skills, and adaptability to a wide range of water conditions. These attributes serve them well in places like the Everglades where natural predators are fewer.

Aquarium Care

Oscars aren’t challenging fish to keep – they’re just involving fish – which I suppose you could argue is a challenge to keep up with. Removing food and replacing water is certainly not a hard task, but oscars need a lot of clean water. 50% – 75% weekly water changes are ideal for these guys.

If your tank isn’t near a water source, I suggest you reconsider the location or invest in something like a python. 10% daily water changes after they’re done eating with a weekly 75% water change is a much better strategy. If you can, it would be worth considering creating an automated water change system for these guys with the ability to “flush” the system. If you keep your tank bare bottom and ensure your water circulation prevents the majority of food particles from ending up on the bottom of the tank, you may be able to get away with less maintenance with a sump and an AWC system, but you’ll still likely have to get your hands wet at least weekly for the next 20 years.

Oscars, like I said, can be destructive (they usually are.) Unless rocks are glued very well to the bottom of the tank and each other, they’re best avoided. Most oscars will accept smaller rocks with relatively few complaints but will often still attempt to move them so be sure they’re not big or sharp enough to easily chip or break the glass if tossed around. In general, rocks are best avoided unless they’re glued because they can often scrape the bottom of the tank even if they’re moved nicely – or worse – your oscar could injure themselves.

They like to dig in sand and gravel, often pushing it around or picking it up and moving it in giant mounds around the tank, so be sure to stir up any substrate whenever you clean the tank to avoid anerobic activity in areas where sand or gravel is deep. You can certainly flatten it back out every week, just know your efforts will be in vain.

Typically, oscars and plants don’t get along. If they don’t shred them, they’ll dig them up or opt to play with them, sometimes carrying them around the tank (not unlike a dog with a stick.) So, if you chose to go with plants, fast growing, floating, and hardy plants are the best option, but avoid investing in expensive plants or equipment as there’s no guarantees it’ll work.

Driftwood and root systems can work for oscars, although, again, if it’s light enough for them to move they will likely do so. Oscars do well with leaf litter that they can play with and shred up. Catappa and oak leaves, twigs, bark, and tough seed pods large enough that they can’t swallow work well. For seed pods, monkey pots, ebano pods, and bael tree pods should fit the bill – the last can double as a floating toy to push about as well since it’s notoriously hard to sink.

Filter intakes and outputs should be well-secured to prevent being moved, broken, or otherwise dangerously damaged in some way. Sponges over the intakes are out of the question, oscars will usually rip them off to play with or shred. Canister filters and sumps are the only two options oscar owners have to efficiently filter all the water, and most employ two canisters at that. You should aim for a turnover of four times per hour, although more is usually better so long as they’re not living in a whirlpool.

Heaters should also be safely secured and housed in a protective case (like PVC) if they’re going to be inside the tank – be sure that the wire is also protected. Most often, the least dangerous and most convenient option for oscars is a sump as everything can be housed in there and the intake and output won’t be played with. It’s generally advised to avoid using carbon in your filtration system with oscars as there’s speculation the long-term use of carbon can cause HITH.

Additionally, be sure to secure the tank with a large rock, heavy weight, or clips to prevent your oscar from jumping to her death.

Feeding Oscars

Oscars are omnivores that eat smaller fish, insects, crustaceans, and vegetation in the wild. Although they do seem to prefer meat the most, being more omnivorous only when meaty foods are scarce. A study done by Winemiller (1990) revealed that the most popular fish to be consumed by wild oscars were benthic catfish, so perhaps they’re best avoided with oscars.

Oscars are notoriously unpicky and known to wag and beg for food when they see you. Pellets are generally the best option. It’s been shown, by many studies, that the level of aggression increases when live foods are used in most large predatory fish, so they should be avoided if you can.

If you don’t want to avoid live food, crickets, mealworms, and redworms are the best options. It’s generally known that feeder fish offer a host of risks with no value for you or either fish involved, especially since oscars aren’t obligate piscivores, they’re best avoided as well.

Oscar Fish Diseases

These big guys are no strangers to water-quality related ailments. And it’s no surprise, really, giant messy beasts in a contained space? Well-seasoned filters and good water change practices are the best defense against most of these things.

Ich (White Spot Disease)

Fin Rot & Tail Rot

Hole In The Head (HITH) or Head & Lateral Line Erosion (HLLE)

Oscar Fish Tank Mates

This is tough due to the limited size of the average aquarium someone usually has available. For most people, the best options are wholly unrealistic, and may not even work. Keeping an oscar with tank mates requires additional large tanks are made available in the event the relationship suddenly goes sour.

However, supposing you have a monster tank, awesome filtration, a large budget for fish food, some skill, and an affinity for monster fish, you can maybe, kind of, possibly, depending on the fish involved (both personality and size), keep oscars with:

Freshwater Stingrays (several species)

Jack Dempsey (Rocio octofasciata)

Breeding Oscars

Breeding oscars is certainly an accomplishment that many keepers hope to achieve some day, and it’s a rare thing indeed to have oscars breeding in home aquaria – for reasons I’ll soon lay out. But I’ll ask you this; should we, as fish keepers, breed oscars at all?

I’ll admit, I’ve thought about it a time or two. It’d certainly be a marvel to watch two 18” long oscars parading 2,000 fry around a 300-gallon tank – or larger. No, those aren’t typos. In fact, reports of 5,000 eggs have been made. Imagine even 800 baby oscars. To feed, to clean up after, to fill your house with massive tanks to raise them in, to eventually find homes for them that will likely be unsuitable and force them to be rehomed – and rehoming is a best-case scenario for most oscars, let’s keep that in mind. Finding 800 new 75-gallon homes (or larger!). Every. Month. That’s some nightmare fuel right there.

Of course, you wouldn’t make money off them. If you managed to run at a minor net loss I’d be shocked. You ever fed baby oscars? They’re bottomless pits. Not to mention your water and electric bills. And the market’s flooded with farm-raised imports at dirt cheap prices. Surely there aren’t enough suitable tanks in the United States to house all the oscars coming from overseas – never mind the ones you’d be breeding.

And, to boot, most pet stores know they’ll eventually get back some of the oscars they sold, and they’ll need to try to resell those, so most won’t take them off your hands. Selling a big oscar is a hell of a lot harder than selling an adorable baby, I’ve seen them sit in a shop for months on end with babies flying out the door. Adorable baby versus something that needs to be transported home in a 5-gallon bucket? Easy choice for most people.

If you have an “in” with a wholesaler (usually through your own fish business or through a pet store) you might be able to unload 500 oscars every so often, but I doubt it’d be more than that. You’d likely need to buddy-up with multiple wholesalers and, unless you’re a store, there’s not much benefit in it for you as they only pay in credit. Usually the pet store owner will “cash out” some of their credit for you and take a fee off the top per fish since it’s their connection and time you’re using to unload way too many fish. You’ll likely end up with 50 cents per fish if you’re lucky, but 10 cents is more realistic. That’s provided the wholesaler even has room for your oscars since they’re imported in droves. Welcome to the hardest $50 you’ve ever earned!

The real hurdle here isn’t breeding oscars, it’s what the hell to do with them after you’ve bred them!

Not unlike convict or jewel cichlids, you’d be lucky to convince someone to take 5,000 oscars off your hands if you paid them to do it. Would it be awesome to see? Absolutely. Would it be a hell ride? For sure. Is it the right thing to do for the welfare of the animals? I’ll leave you to decide but I’m firmly planted in no.

For those reasons, I’ve decided not to include information on how to breed oscars. This isn’t a judgement against anyone who does or anyone who wants to breed them, but we all have to stand for something, am’mi right?

Types Of Oscars

Oscars come in a variety of colors, morphs, and patterns that might surprise you. While the number of variants isn’t as high as some other species, it’s still an impressive selection, nonetheless.

Further Reading & Resources

Seriously Fish – Astronotus ocellatus

Animal World – Oscar

Smithsonian Mag – It’s Official: Fish Feel Pain