Question from my mother about her oscar and Jack.

Maybe. It depends if there is a large difference in sizes and the attitudes. Both can be difficult or laid-back. You'll never know until you try but be ready to separate them.
 
From my experience in the past, I had a Tiger Oscar with two Jack Dempsey s. The oscar was considerably bigger but they became a "family" some how and The Jacks followed around the Oscar as if they were it's babies or something. Eitherway be prepared for cohabitation or a brawl. :D good luck to your mom. Try mixing up the decor before adding the Jack
 
I've had good luck keeping the two species together but like excuz said a lot of it depends on the temperament of the fish and of course the size of the aquarium. What size is it anyways?
 
Actually, a 55 is too small for an Oscar even if it is the only fish in the tank. You need a minimum of 75 or a tank with a similar footprint. Oscars can get to 18" with the average running about 15-26". A 55 is only 12.5 wide which is too little for a full grown Oscar to turn around in.

Yes, I do have Oscars (5) and so far my largest is at 17" and still growing. The smallest tank I am using is a 75 and the largest is 125 with a 1200gph flow rate filtration that will support a 200 gallon or larger tank.
 
someone told her it's safe to put 2 oscars in a tank that size, so that's why she wanted to put her oscar and my baby jack together
 
Actually, a 55 is too small for an Oscar even if it is the only fish in the tank. You need a minimum of 75 or a tank with a similar footprint. Oscars can get to 18" with the average running about 15-26". A 55 is only 12.5 wide which is too little for a full grown Oscar to turn around in.

Yes, I do have Oscars (5) and so far my largest is at 17" and still growing. The smallest tank I am using is a 75 and the largest is 125 with a 1200gph flow rate filtration that will support a 200 gallon or larger tank.

I agree that based on size an oscar should really have a 75g. Some people still think differently though.
 
Actually, a 55 is too small for an Oscar even if it is the only fish in the tank. You need a minimum of 75 or a tank with a similar footprint. Oscars can get to 18" with the average running about 15-26". A 55 is only 12.5 wide which is too little for a full grown Oscar to turn around in.

Yes, I do have Oscars (5) and so far my largest is at 17" and still growing. The smallest tank I am using is a 75 and the largest is 125 with a 1200gph flow rate filtration that will support a 200 gallon or larger tank.

OOps! That was supposed to be 15-16". Sorry for the typo.
 
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