Really good answers everyone, I also think from experience that for a 75gallon that midas will be kept by himself (assuming your getting a male).
But for a 125gallon Ive kept my 12" male midas with 10" tiger oscar, 9" tiger oscar, 7" male midas (offspring), and bunch of raphael catfish and common pleco (free adopted from petco). Even that most fish will get a beatting here and there.