Average adult size for a full grown ranchu and oscar fish
Ranchus reach to about 6 to 8 inches but can get bigger if they are treated well and kept in larger tanks.Oscars actually will continue growing depending on their tank size. I have seen oscars that were over 12 inches long and almost just as high. These are both fish that need lots of room and tank care to be sure the water is clean enough for them (lots of waste).
My sisters Oscar was about 13-15 inches the ranch us get 6-8 and oscars need a BIG tank. My sisters was in a 150 gallon.