how big would four oscars get if they were put in a diy tank that is 10 feet long, 6 feet wide, and 4 feet tall. iam guesing they would get to two feet long. also there would be other fish would be catfish and an arowana.
I think they would do just fine if you buy them small and allow them to grow together.
getting 4 full grown oscars who have never seen eachother and putting them in the tank all at once could work... but I wouldnt introduce them one at a time because once one of them establishes territory your gonna have a fight on your hands.
i think the largest oscar in captivity is probably one of the oscars in that guy one MFK that has the 50,000g tank and i think his oscar is close to 18in but i dont know if it is still growing or not but i think your oscars could get to a similar size to that one