small pellets, floating is the best. oscars are pigs. they will eat even when full. i started with live brine when 1in, and went to pellets. you can control the over feeding with the pellets. put 3 in and wait till all gone. pellets expand when they get wet. i had mine for 10yrs it got 10in. 1in per yr,in a 55gal. he would eat 8-10 lg goldfish in 1 feeding. but as for live goldfish beware of infected feeder goldfish. one cannot tell till it is to late. my died from a bad batch of goldfish, and the lfs told me that is the chance you take when you feed live foods. when he gets bigger go with med pellets, then lg ones.