I think it varies between different fish. I've had numerous types of food that some fish would eat and others just wouldn't accept it. Then I'd use tilapia and everyone would love it. So for me it's tilapia, pellets that I have in a dog food bin that I just take a scoop and feed (massive, carnivore sinking, sinking cichlids, bottom feeder tablets, shrimp pellets), I also sometimes feed bloodworms and beef heart to my grow outs. I used to feed earthworms and they'd love it, but then they'd start to get a little bit aggressive and with some of the size differences I have in my tank the big boys may mistake a smaller poly for a worm itself.