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

Its probably to do with a lack of space. Cichlids can and are aggressive to each other if theres not enough room to stake out a territory. Maybe having some pipes or caves where the smaller can hide might work but you deffinately need a larger tank. For two full grown oscars i think you are talking at least 125 gallons.
It sounds like the bigger one is a male and the other one could be either sex.

I am sure this is because of the small tank you have. Once you have a larger tank then this will lessen
http://www.solodvds.com/oscar-fish/oscar_fish.htm
check this link out for size of tank needed and any other info needed.
Then you can use the 20 gallon to buy smaller type of goldfish, not feeders, to feed your oscars. Feeders can carry disease that will kill or make your oscars ill.

We have rocks hiding spots for each oscar in the tank. They have their spots that they like to stay, usually! Louie is now at the top of the water in one corner of the tank. He's breathing and his fins are moving and not clamped. Most of the time he's laying tilted to the side, but if I walk over to the tank he will perk up. I have never seen him stay at the top of the tank like this before! Do you think he's sick?

Feeding fish to others is something we dont encourage on this forum. Cichlids have no need to be fed live food at all and can get all the nutritional needs through dried and frozen foods.
If goldfish were fed goldfish then it could be compared to a human eating nothing but big macs, hardly a great diet.

It sounds like he is really stressed with having to live with a bully, all you can do is move one of them out until you get another bigger tank or he may end up being killed or die from stress.
If it was my fish then I would either get a seperate tank set up or take the stressed one back to the store until i got the bigger tank but you would need to get another oscar that was bigger than the bully, and it may even turn out that the big oscar might not take any other oscar being with him.

some fish do eat live food, just like snakes eating live mice or gerbils.

Yes they do but theres only a few types of fish that will only take live food.
All cichlids can take prepared food and theres no excuse for people who feed their cichlids live prey.

What do you think about a divider in the tank until we can get to the store? We plan on going this afternoon to get a bigger tank. The only other thank I have is a 1 gallon betta tank, I don't think this would do at all!

EDIT-- My husband can get his hands on a 10 gallon like right now. Will this be OK for the smaller one until we can get a bigger tank?

Yes, but really you might have problems with the bullying in the bigger tank as well, but at least the little one should be able to hide as long as you have lots of hiding places.
Once you have the bigger bigger tank set up make sure the sicker one goes in first for a few days to build its confidence up and then try Rambo.

Any suggestions on making the transition easier for Louie, he is the one that we are going to move.
We don't have 2 heaters, what about water temp?
Extra Gravel?

Poor Louie!

Without another heater then its going to be hard as they really do need a tropical tank. Use water from a kettle to bring the water up to temp and place the tank somewhere really warm and hopefully that might be ok until you sort out his permanent home. Once its all set up move him in with half tank water and half kettle and dechlorinated water. Try to get a little bit of gravel on the bottom,just enough to cover the glass and a small filter as well if you have one, and a large cave for him to de stress in

We have a filter and an additional air pump, so this isn't a problem. My husband aslo has 2 submersible water pumps that he is going to rig up to pump water from one tank and then back to the other, that way the water will be heated. I just hope this plan works! We have well water, so we usually just fill from the sink with a hose and use heated water, so this should work for the filling part.
I have prime, proquatics bicteria starter, and salt. Any thoughts?

Thank you so much for answering me so quickly! I am typing and reading to my husband and he gets this straightened out. We are running around like CRAZY!

I really appreciate all this help, you are a lifesaver!

I wouldnt add any salt just now, is the filter already being used in the other tank or is it running for the first time after being out of action for a while? If so then pumping the water round from both tanks should be ok to give the filter enough bacteria though keep an eye on the ammonia and nitrites.
Hopefully your hubbys plan of transferring the water from tank to tank works.

We'll see. Sometimes I feel like I live in Monster Garage!