Oscar Tank Size – Complete FAQs

There has been a lot of controversy over how big an Oscar fish’s tank should be. There is however no need to join the confused queue as this article will answer all Oscar fish tank related questions.

What is the proper Oscar fish tank size?

On the question of what tank size is best for an Oscar fish, the answer is simple. Aim to have at least 50 gallons in tank. Oscars can grow to as much as 20 inches so you need to get them a tank with good swimming space for their body.

Can Oscar fish live in a 10 gallon tank

No. Oscar fish are actually on the big size. They grow as big as 20 inches in the wild. It is also very important to note that they grow very fast. Like you can literally have a little fish right now and witness them grow into giant Cichlids in no time at all

If you put your Oscar fish in a ten-gallon tank, it would turn out to be a severe waste of your money and huge harm to your fish. Oscars are big fish. They will never be healthy in a tank that small.

Why 10 gallon tank won’t work!

When I emphasize the fact that ten gallons won’t work, I have very strong reasons for this. All of these reasons are backed by expert research. Irrespective of what you have been told by pet store attendants, Oscar fish are meant to grow big. They are ravenous fish who eat a lot. Their waste product is also reminiscent of their appetite. This means that they poop as much as they eat.

A small tank will need cleaning more often because of their giant waste product. But perhaps more importantly, your Oscar fish may develop a variety of health issues from being in a cramped space. Under no circumstances should you put your fish in a ten gallon tank. It is cruel and wrong.

How many Oscar fish can stay together?

Oscar fish are not social animals. They don’t need to live in groups and are completely self sufficient and independent of other fish. In fact, judging by how territorial they are, they may be best left alone.

Negating popular belief that animals get lonely when they’re alone, Oscar fish so not get lonely. In fact, they may actively detest having other fish around. Even if the fish is also an Oscar.

To answer the question of how many Oscar fish can be kept together, therefore, here is the simple answer; You can keep two Oscars together in a tank, maybe even five, but never three.


The answer is simple. Oscars, though not particularly social in their behavior, do have a tendency to pair off. Especially where there are females. If a male and female Oscar pair off, therefore, the third Oscar may be isolated and therefore face some challenges.

Some of these challenges include aggressive behavior from the paired-up Oscars who now not only view it as an outsider, but also as an invader. This situation may then result in the Cichlids attacking the single Oscar.

Will Oscars attack each other in the same tank?

Oscars are highly territorial fish. As a general rule, Oscars prefer their own company and are likely to attack fish that they consider as intruders. Oscar fish are not always territorial, but there is really no way to identify the potentially aggressive ones when they are just fries.

This is yet another reason why you have to get a tank that is sizeable and appropriate for the fish you intend to keep in it. The more space the Oscars have to move around in, the less the likelihood that they would fight each other or be super aggressive.

What size tank do I need for 2 Oscars?

Now if you need at least 50 gallons for one fully grown Oscar, how big should a tank for two Oscars be? The simple and straightforward answer to that is 100-150 gallons. In fact, I would suggest that you just get at least 125 gallons for 2 Oscars.

It is important to know that Oscars will soil their water at double the usual rate if there are two of them in the water. They will require double everything. Double the water, double the filter power, double the space, double the food, and thus will produce double the mess.

In a nutshell, the barest minimum tank size for 2 Oscars is 100 gallons. But just to be safe, aim for 125- 150 gallons.

How many Oscars can you put in a 55 gallon tank?

One. The minimum tank size for one Oscar fish is 59 gallons. 55 gallons is only a little bit more and will not automatically translate to more space or even enough space for one more Oscar. Please budget at least 50 gallons for each Oscar fish and multiply that by the number of Oscars you intend to keep.

Oscars are notoriously messy fish and require a lot more care and attention than most other fish species. These Cichlids produce a lot of waste so frequently. This makes water changes a given necessity.

This means that the smaller the tank that you house them in, the more frequently you will have to clean them and check the water.

How big a tank should I get for breeding?

Ideally, you shouldn’t have one tank for breeding. You should have two. The reason for this is that Oscars have the tendency to be infanticidal and this can cause you a lot of waste and stress. You’ll need to separate the fry from their parents as soon as possible after they’re hatched.

The tank that will contain the two-parent fish should be about 125 gallons in size. This will give them more than enough space to do their mating dance and also find a nice spot to lay their eggs. It may also help keep the fry safe for a while before you are able to evaluate them to their own tank.

Do Oscars grow to the size of the tank

Oscar fish are meant to grow big. They are biologically designed to grow as big as 20 inches and live up to 20 years. Captivity may shorten their possible growth length to about 18 inches and life span to about 17.

It is however very important to note that the notion of an Oscar only growing as big as the tank will let it is wrong. Oscars who are cramped up in the small tank will be unhealthy and may die in as little as two years instead of the 18 that they would have lived.

Oscars do not grow to fit their tank. They fall sick and die. That is the better, more accurate way to put it.

What happens to Oscars in small tanks?

The fish will try as much as it can and struggle to grow, but with the resistance of the tank, the short swimming and exercise space and the trapped feeling that comes with it, your Oscar slowly deteriorates and then die. This is not to be mistaken for an animal that grows to fit its tank.

If I keep my fry in a 10 gallon tank, how long before they need to move?

Oscars grow really fast, it is therefore super imperative that you know that you won’t have a lot of time at all. When you pick up your small Oscar fish, do not be shocked to see that they grow as fast as 1 inch per month.

Oscar fish babies are as small as any other tropical fish when they are young. They can be as small as 1 to 2 inches. Under the right circumstances and conditions. However, they can grow at a rate of 1 inch per month, and may reach their fully grown size in ten to eighteen months.
This means that you may not have a lot of time to prepare if you are not already prepared for them at the point of adoption.

It is best to get your tanks before you even buy them. Or at least, make sure that the new tank is ready shortly after the young fish is home for the first time.

Tank size issues to note in Oscars

The size of your tank can determine a lot of things in the life, health and even death of your fish. Here are the ways in which your tank size may affect your Oscar fish health and well being

Faster water pollution

The smaller your tank, the smaller the water and thus, the faster the water is polluted because Oscar fish actually make a lot of mess. You may need to change the water more often and even then, it may not be enough.


Because the water is getting messy faster, your water filter will need to be powerful and work overtime. This in itself isn’t particularly injurious but it may increase wear and rear on the filter and increase chances of malfunction.


As we have already established, Oscar fish are rather aggressive and territorial. If you keep two fish in a space that is too small for them, they are very likely to fight. This may cause injuries to one or both fish.

Whatever injuries they sustain may not heal fast enough because of the aforementioned likely bad water conditions.
Injuries left unhealed could fester and actually degenerate into a life-threatening situation for your fish.

Lack of exercise

The smaller the tank, the smaller the swimming space for your fish. This may mean that your fish may not get enough exercise. Oscar fish love to swim. They love water current and fast water. The last thing they need is a tank that isn’t even big enough space for them to goof around.

Lack of exercise can increase impaction and constipation. This can slow them down and make them lose appetite. It could even grow into a worse situation for them in terms of their health.

Water change

Oscars are very sensitive to sudden changes in water parameters. They are also susceptible to common tropical fish diseases such as Ich, Dropsy, Fin Rot and Tail Rot. Clean water is very essential to the physical and mental health of your Oscar fish. In fact, starting from a certain ammonia level, they will start to be distressed.

If your fish already have other diseases or infections, it will get worse because of the bad water. In fact, if your Oscar has even a tiny little wound from slapping against something, the bad water is sure to make it way worse.

What is the perfect water condition for Oscar tank?

The best temperature level for your Oscar Fish is between 75 and 80 degrees Fahrenheit (23 – 27 Celcius). They may show a particular preference for a pH balance that ranges between 6 and 8. The regular Oscar fish will be okay in a wide range of water hardness levels. They have however shown more promise in waters of around 12dH – 15dH.

One other recommendation that I would make is that you get the best water filtration system you can find. You should also invest in a good aquarium thermometer as this will help you keep track of the water such that it neither gets too hot or too cold. Your fish will definitely be stressed out if the temperature isn’t comfortable or if the ammonia levels spike too high. This may lead to loss of color, loss of appetite and may even cause sickness and death.

Can I just keep my Oscar in a tub?

No. You can’t just keep your Oscar fish in a tub. Oscar fish have very specific needs. These needs will be more difficult to fulfill in a tub. But perhaps most saliently, Oscar fish are jumpers. If the tub is uncovered, your Oscar fish will likely leap right out of it at some point.

This can be very dangerous to it. The fish could get injured and be sick for a long time, or if it is unlucky, it may die from the lack of water. It is therefore not a risk worth taking.