Why get an oscar?

Oscars have the very well deserved nickname “Water Dogs” because of their big personalities and ability to recognize and interact with their owners (not unlike man’s best friend). If you have a large enough tank and are looking for a great fish to put in it, oscars are definitely worth considering. They are very entertaining fish and oscar owners never seem to run out of intersting stories to tell about their fish.


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What sized aquarium should I use?

Aquarium – Allot at least 50 gallons for each oscar. Oscars normally grow to 12″ – 14″ in length (not including their tail). These are large, messy, territorial fish. Using a tank any smaller than this and you are highly likely to run into aggression and water quality problems. Also, keep in mind that longer, wider tanks are better than taller ones. Bigger footprint = more territory. Oscars also grow very quickly. They generally average 1″ per month up until they are around 7″. After that they slow down to around 1″ per year. But because of that initial fast growth rate, it is highly recommended to start off with a large tank. Otherwise, you would have to be upgrading tanks every couple of months, which can become expensive and stressful.

A 10″ (not including tail) oscar in a 20 gallon hospital tank. This oscar is not fully grown yet,
so you can see why a small tank like this isn’t even close to being sufficient for an oscar!

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What kind of heater should I use?

Oscars are known to destroy glass heaters. The best way to prevent this from happening is to get either a stainless steel or titanium heater or at the very least a heater guard. The general rule for heater size is 3 – 5 watts/gallon. Like most tropical fish, 75-80ºF (24-27ºC) is a good temperature range and make sure that it’s stable.

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What kind of filter should I use?

Oscars are messy fish. With hang on the back (HOB) type filters you should aim for a turnover rate of at least 10x the tank volume per hour. For example, if you have a 55 gallon tank, you would want an HOB filter (or a combination of HOB filters) that does at least 550 gph (gallons per hour). Canister filters hold much more media than HOB filters, so they are more efficient. When using canisters, you should aim for 3x – 5x the tank volume (i.e. 165 – 275 gph for a 55 gallon tank). True wet/dry systems are just about as efficient, if not a little more efficient, than canisters so the same 3x – 5x rule applies. If you are using a combination of canister & HOB filters, you should double the gph that the canister does then add it and the gph of the HOB filter and aim for 10x.

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Does my oscar tank need a lid?

Oscars have been known to jump out of the water (especially when taught to jump for food) and they get large enough to easily be able to knock open an aquarium lid. To avoid finding your fish on the floor, it’s a good idea to either put heavy items on the lid or secure the lid with velcro. Also, don’t encourage your fish to jump for food.

Securing a tank lid using adhesive velcro. It may not look pretty, but it will keep your fish in the tank, rather than on the floor.

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What substrate should I use?

Both gravel and sand are perfectly fine substrates for oscars. They each have their good and bad points, so really it’s just a matter of personal preference. Either way, just make sure it is rinsed really well before adding it to the tank. Oscars do like to dig but there’s really no need to have more than about 1 1/2″ of substrate.

The nice thing about sand is that it’s more compact, so the waste mostly just sits on top. That makes it a little easier for the filter and a gravel vac to pick up (just hold the gravel vac about an inch or so above the surface of the sand). With gravel, however, there are lots of open spaces for waste & uneaten food to get trapped in. Even when gravel vacuuming, it’s difficult to get it all out.

Probably the biggest downside to sand is that it develops anaerobic pockets fairly easily. Those pockets can start to form hydrogen sulfide gas. If the pockets get disturbed and too much is released into the water, it could poison the fish. To avoid those pockets, you have to stir the sand occasionally (doing it with the weekly water changes is generally sufficient).

There is a danger of sand getting sucked up by the filter, which can ruin the impeller (finer sand is more of a problem than coarser sand). Generally, though, if the intake is at least 6″ – 8″ above the surface of the sand, it shouldn’t be a problem. If that doesn’t work, there’s also sponge prefilters that will help to keep the sand from getting sucked up. Most canisters have the impeller after the filter media, so if any sand does get sucked up, it usually doesn’t make it to the impeller.

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What decorations can be used?

Oscars are large fish and like to have open swimming areas, so a tank packed full or rocks, driftwood, plants, etc. wouldn’t be a really good idea. That said, there is nothing wrong with a few decorations. Just make sure there are no sharp edges that the fish could cut itself on. Some of the most common decorations in oscar tanks are large terracotta pots, driftwood, rocks and artificial plants that are aquarium safe. Pots should be large enough for the fish to get into and turn around in without getting stuck. Pots, driftwood, and rocks should also be heavy enough so that the fish can’t move them around easily or knock them up against the glass.

Sample of a tank decorated using a pot, driftwood, and artificial plants (in this case, the artificial plants are all attached to the driftwood and pot using plastic zip ties).

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Can plants be used?

As a general rule, oscars and live plants don’t mix. Most oscars do okay with live plants when they’re little, but when they start reaching maturity and start getting territorial, they tend to rip the plants to shreds (there are of course exceptions, but they are rare). So it’s best to have artificial plants. The oscar will still try to move them but it shouldn’t be able to tear them up.

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What sort of water does my oscar need?

In the wild, oscars live in water that is soft and slightly acidic. But like most fish, they can adapt fairly well to a wide range. So as long as your KH is somewhere between 50 and 300 and your pH is between 6 and 8, they should be fine. There are products out there that you can use to adjust those things, but changing them can cause more problems than leaving them alone. Stable and not quite perfect is much better than constantly fluctuating and trying to get it perfect.

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What diet does my oscar need?

Diet – The absolute best food for oscars is good quality pellets. They are specifically designed to meet all of the oscar’s nutritional needs. Some of the most commonly recommended ones are Hikari (Staple, Gold, and Biogold), HBH (Oscar Show & Oscar Grow), New Life Spectrum, and Omega One.

Treats – Even though pellets meet their nutritional needs, oscars appreciate a bit of variety in their diet. There are many treats that can be fed to oscars including crickets, earth worms, red worms, meal worms, krill/shrimp, snails, beefheart (but no other mammal or poultry meat), and some will even eat veggies like peas, spinach, and lettuce. Most pet stores will sell crickets, earth worms, meal worms, and red worms for fairly cheap. Although most people have a nice array of insects available in their backyards, giving them to fish can be risky because they could have come in contact with pesticides, which are poisonous to fish. Also, mammal and poultry meat contains a lot of unsaturated fat which fish cannot digest due to their low body temperature. The fat gets stored in the liver and can eventually kill the fish. Beefheart is an exception because it contains almost no fat.

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Should my oscar have feeder fish?

Generally, feeder fish are a bad idea. Most of the ones that can be purchased at the store are kept in really horrible conditions. They are very unhealthy and highly likely to introduce diseases into your tank. Even if they look healthy, there’s no guarantee that they actually are. The ONLY way it would possibly be okay to use store bought feeders is if you quarantined them for at least 2 weeks. To get around using store bought feeders, you could breed them yourself. However, you would have to keep them in just as good conditions as you would any other fish. You can’t overstock them, you have to feed them a good diet, and you have to keep their tank clean. Otherwise they would be no better than store bought feeders. Considering all of that, in most cases it isn’t practical to use feeders at all; especially considering all the other safer, cheaper alternatives. But if you did use them, they should only be a very occasional treat and NEVER the staple part of the diet.

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What should I do to get ready for my new oscar?

Cycling – Once you have your tank set up with all the equipment, it is very important that you cycle it. You can read more about the nitrogen cycle and how to cycle tanks HERE. It is highly recommended that you either use the fishless method for cycling or use Biospira which is a product that contains all the bacteria needed to cycle a tank almost instantly.

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What are the different types of oscars to pick from?

Once your tank is cycled, it’s time to pick out your new oscar(s). Although all oscars are the same species (Astronotus ocellatus), there are several varieties available. They have been selectively bred for color, pattern, and fin shape, but all their care and requirements are the same. These are the most commonly available colors & patterns:

  • Tiger – These have a green/black base color with an orange stripe pattern.
  • Red – These have a green/black base color with solid orange on their bodies.
  • Common/Wildtype – These have the same patters as found on wild oscars. They have a green/black base color with yellow/pale green stripes. They basically look like a tiger without the orange.
  • Albino – True albinos would be pure white with no other color. However, what most people refer to as albinos have a white/pale yellow/pale orange base color with darker orange markings (either tiger or red), but no other dark colors such as black or grey.
  • Lutino – These look like the albinos, but they will also have black or grey which generally will be on the edges of the fins.
  • Blueberry/Strawberry – These are albino/lutino oscars that have been dyed blue or red. Dying fish is a really horrible process. Most fish don’t even survive the process and the ones that do are generally more prone to illness, have shortened life spans, and lose their color after a few months anyway. Please do not buy dyed fish.

These are some of the less common varieties:

  • Veiltails/longfinned – These come in all the color varieties, but have longer fins
  • Sunshine – These look like albinos, but have yellow markings instead of orange
  • Golden – These look like reds but have yellow markings instead of orange.

When actually selecting an oscar, you should first make sure there are no sick/dead fish in the tank. The color/variety is really your own personal preference, just make sure to pick one that is nice & active.

Young lutino oscar
Red oscar

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How do I acclimate my new oscar to the tank?

Make sure to float the bag in your tank for at least 20 – 30 minutes to allow the temperature in the bag to slowly reach the temperature of the tank water. Also, during this time you need to slowly acclimate them to your water’s pH and hardness. This can be done by adding a little of your tank water to the bag every 5 minutes or so. It might be helpful to test the pH of the store’s water to see how far off it is from your own. If it is drastically different, then the acclimation process should be done a little more slowly. After the fish is acclimated, use a net to remove the fish from the bag and place it in the tank. Never dump the water from the bag into your tank.

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Why is my oscar sulking?

Oscars can be moody fish and don’t like changes in their environment. It’s not uncommon for oscars to sulk for the first few days. Leaving the lights off and trying to keep the traffic around the tank as minimal as possible will help the oscar feel more comfortable. Just make sure your water parameters (ammonia, nitrIte, and nitrAte) are all in check and watch out for any signs of disease.

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How can I tell if my oscar is a male or a female?

It is very difficult to determine the sex of oscars just by looking at them. Pretty much the only two ways to do it are to “vent” them and watch them breed. Venting is done by looking at the openings on the fish’s belly. The one closest to the head is the anus and the one closest to the tail is the vent (reproductive opening). In males, both openings should be roughly the same size (oo). In females, the vent will be larger (oO). That said, venting is somewhat controversial. Some people say it doesn’t work and others swear by it. But even the ones that say it works say it also takes some skill and experience to do it reliably. The only other way to determine sex is to witness a successful spawning. The first indicator of sex will be the breeding tubes. Males will have a pointed one (V) while females will have a more blunt, rounded one (U). Also,the female will obviously be the one laying the eggs. However, sometimes two females will go through the mating ritual so even though one lays eggs, it doesn’t necessarily mean the other is male. That’s why it has to be a successful spawning that results in fertilized eggs. Then, if there where only 2 oscars, you can assume the other one is male.

Male oscar vent (left – oo) & female oscar vent (right – oO).

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What about tankmates?

Although there’s actually a wide variety of fish that can be kept with oscars, whether they should be kept together will depend a lot on tank size. With other large cichlids (such as Jack Dempseys, Green Terrors, Convicts, Firemouths, Acaras, etc.) you have to keep in mind that the more large, aggressive fish you have, the more space you need to give each fish. A lot still depends on the individual temperament of the fish (some will not tolerate tankmates no matter how large the tank is), but even the most passive fish can turn aggressive if it’s really crowded.

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