Is there a general rule of thumb for adding different size Oscars into a tank? Pet Smart told me that anything more than 2 inches in difference and the smaller ones can get bullied. The reason that I am asking is "if" I get this 300 gallon tank that I'm looking at, I would like to add my 4" O, my 2 2" O's and my 2 turquoise severums into the one big tank along with my 2 plecos. I know that it is better to introduce them all at the same time and there is less likely a chance of aggression and/or territorialism (is that even a word?).

you cant really tell until they are together, they will either like each other or not, you just have to try it out, you could ask the person you buy them off if it doesnt work out they will they take them back, im afriad its trail and error

From my experience, you really only find out how your Oscars are going to behave with other tank mates when you put them together. You certainly shouldn't be putting in very small fish because you're asking for trouble. There are not that many other fish out there that grow at the same rate as Oscars. So when you buy other fish to put in your tank, I would definitely get them as adults, or big enough so the Oscar will not be able to eat them. How big you may ask? Probably no less than 4 inches

That's what I'm concerned with about the severums. Not sure if they're going to grow at the same rate as the O's. Couple other sites I read said they will grow to about 5 inches in the first year. Hopefully the sevs don't wind up being food lol.

like the others have said, its hard to tell until you put them together.

I have a 5" Red Oscar that is dominant in the tank. I put my 3.5"Lutino Tiger Oscar with the Red Oscar about a month ago and the larger Red Oscar bullies it and treis to keep the smaller Lutino on one side of the tank. Then a few weeks ago I added a 2" Tiger Oscar and the larger Red Oscar doesn't bully much at all. The larger Red Oscar allows the much smaller Tiger Oscar swim around with him freely. For some reason they seem to like eachother while the Lutino is not allowed to swim around the tank freely by the Red Oscar.

So, it just depends. These fish are very intelligent and make their minds up for themselves.

i purchased my sev. when he was 4", my oscar 6", that was a couple months ago and since my oscar is now 8" and the severum is 6". so they grow at about that rate in my 75 gal. tank. hope this helps.

So, I moved my big O and my other pleco into my 125 temporarily so that I could drain my 55 and move my 90 into a different spot. The O's seem to get along ok. The Sevs have taken to hiding. Behind the heaters and the canister filter pipes. I have a feeling that I am going to have to move the big O back out here shortly. Kind of a bummer. The good news I found out though, when I fed the big O bloodworms, the lil O's went crazy for em. Had to throw another block in there. HAHA. I may consider moving the sev's into the 90 and keeping the 3 O's together in the 125. Just a thought.

So, I'm not having any luck. I put my big O in the 125 temporarily so I could move my 90 to a different wall in the dining room and he killed the albino O. Was only in there for a couple days. The sevs which I was more worried about cause they were a lot smaller managed to stay unharmed. Immediately did a water test and moved the big O back to the 90.

Sorry to hear of the loss of the Lutino. Oscars are just picky about who/what is in their territory. I have one of my O's in a 90 with a pink convict and a common Pleco. The O nips at the Plec and he rarely responds to it, sort of like "Go away kid, you're bothering me." Sometimes the Plec will give the O a shove. Both the O and the Plec are at least 12" and the Con is 4-4.5". The Convict likes to try to incite the other two to fight. Like a bunch of kids; fight and make up, fight and make up.