Feed him a mixture of floating pellets, I started out with the md size hikari gold pellets for my oscar, now he eats the large floating type. I also feed him frozen bloodworms, frozen brine shrimp, even frozen shrimp. Avoid feeder fish from the pet store, its cool to watch em get eaten, but they have no nutritional value and they can cause your O to get parasites. I lost 2 small baby O's to lfs feeders, they had a long white thread like parasite coming out of there rectums. The O will beg every time he sees you but avoid over feeding him. I give mine a day of fasting about very week. They def grow fast. btw what type do you have.? I have raised red, tiger and albino. My red is now 10 I had a footlong tiger. Gave him up for adoption to a larger tank. Also get a pleco to eat up the scraps and upgrade filtration because they are the messiest fish ever.
GL raising him