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My husband has a 20 gallon (yes I know its too small, we are trying our best to get them a bigger home ASAP!) aquarium with 2 Tiger Oscars. Rambo (he got this name because he is so aggresive) is about 4" long and Louie is around 3", this includes the tail. We haven't had them a month yet and I swear they have doubled in size, its amazing how fast they grow. When we first bought them they were the exact same size.

Rambo is ALWAYS chasing Louie around the tank. It seems like he never gets a break sometimes. He is constantly harrassed.

~Why is the behavior happening? Is Rambo just the more aggressive, dominant fish?
~Does it have something to do with the lack of space that they have? If so, should we sepearte them?
~Is it possible the we have a male and a female?


Also, Rambo gets more food than Louie does. Is this the reason for the difference in size?

I am just afraid that Rambo is going to harrass him to death!

Thanks for the help

space is probably one of the reasons for your oscars aggressive behavior. also sometimes it just depends on their personality. when i first got oscars i had 2 each about an inch in 10 gal they along fine until they started to grow. i ended up having to separate them and got a bigger tank.

I wish I could be of more help to ya, but you are under the gun - Oscars grow incredibly FAST for their first 10 months or so.
LOL, If ya listen real close ya can hear their skin & scales stretching.

Why is the behavior happening? Is Rambo just the more aggressive, dominant fish?

Quite probably.

Does it have something to do with the lack of space that they have? If so, should we sepearte them?

It's from not only the lack of space, but the fact that your pair are growing up. They'll be starting to feel their "Teen Angst" soon so it will only get worse.
You may need to separate them, but with only 20gallons of space, it's not gonna be anywhere near enough & it's gonna stress them anyway. Even if ya had another empty 20, it's still only gonna give you maybe a month reprive. You'll still have to get a 90 or bigger to stop the behaviour you're seeing.

Is it possible the we have a male and a female?

Possible, but without an experienced person to "vent" them, you may not know till one or both lays eggs.

Rambo gets more food than Louie does. Is this the reason for the difference in size?

Yes, this is the most likely reason for the size difference.
You can try hand feeding them to make sure Louie is getting his fare share of the food.

I am just afraid that Rambo is going to harrass him to death!

Unfortunately this is a very real possiblity.
I realize you are already aware of this and you say you are trying to accomplish it, but you really do need to get them into a bigger tank.
Again, I wish I could give ya better news, but until you have more room for them, it's only gonna get worse.