10 questions about keeping pet oscars

• Author: Richard James

1. How large will an oscar grow?

Oscars grow quickly! You bring home a 2” fish from your local fish store with his big puppy dog eyes. You love him and feed him and within just a few months he measures 10” or more. When kept in the correct environment, oscars can easily reach around 12”, and 14” is not unheard of. Eventual size is something that you must take into account before purchasing your oscar. They will need a tank which holds a minimum of 55 gallons, and 75 gallons is better.

It is not true that an oscar will only grow to the size of its tank. It is however true that a large oscar kept in a small tank will be a miserable experience for everyone involved.

2. Do oscars bite?

For a single oscar, we aim for a minimum of 75 gallons, followed by a further 25-50 gallons per additional fish. As oscars grow to around the 12” mark, they not only need ample space to physically swim in, but they also produce A LOT of waste. Oscars eat lots and poop lots. Not only that, but they are incredibly messy eaters. Oscars don’t just teeth in their jaws, they also have them in their throats. If you’ve ever watched an oscar eating fish pellets, you’ll have seen the cloud of ‘dust’ that comes out of their gills whilst they're eating. This uneaten food then builds up in the tank and breaks down, raising the ammonia levels. Oscars are also incredibly strong. They will happily rearrange the rocks and decorations you have lovingly placed around their aquarium. To reduce their ability to move rocks, you should use larger, heavier rocks. Large rocks in a small tank won’t allow the oscars enough swimming space.

3. What size tank for two oscars?

A forever tank for 2 oscars would need to be 100 gallons or more. Anything smaller won’t give the adult oscars enough space to swim around in and you will become a slave to water changes. A 100 gallon tank will probably measure in the region of 72½” x 18½” x 19 3/8″ (L x W x H). This is a good sized tank for your oscars. Even once you add in substrate and large rocks, there will still be plenty of space for your two oscars.

4. But my oscars are juveniles, what size tank do they need?

Clearly a 3” juvenile oscar will be fine in a smaller tank, but we still recommend starting off with a tank large enough for the adult fish. Oscars grow like weeds! they can easily put on 8 to 10 inches in a year. This often catches people off guard. They set up a 40 gallon for their two inch oscars, and have every intention of replacing the tank before the oscars reach maturity. The problem is, real life throws spanners in the works. one month the car needs fixing, the next the eating has packed up. Before you know it, the oscars are 12” long and the tank still hasn’t been replaced. Start off with their forever tank, and you know you’re sorted, no matter how quickly they grow.

5. What do you do if you have too many oscars in a tank?

If you find yourself with more oscars in a tank than you should (whatever the size of the tank), there are a few things you can do to improve the oscars situation.

• Re-home one or more oscars – This may seem like a drastic step, but if you can reduce the number of fish in the tank, those that are left will have more space. It can be tricky finding someone who is prepared to offer space for a large oscar. Unfortunately, there are many oscars in need of a new home. Ask around your local fish club and in your local fish store. Someone may know of a member or customer that has large tanks and is happy rehoming fish. The Ohio Fish Rescue are a great example of an organisation helping rehoming large fish.
• Add more filtration – Because oscars are so messy, the waste builds up quickly in the tank. Adding a second or even third filter can increase circulation and speed up the removal of particles in the water. Servicing those filters removes that waste from the system altogether.
• Change more water – No matter how many filters you add; you will still need to change water in your aquarium. Filters are great at converting the fish waste into relatively harmless nitrate, but that nitrate can build up to harmful levels. The best way to get the nitrates out is to drain off around 50% of the tank water each week and top it up with fresh water.

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