Different foods for different fish

[Swaggy]

Ok so I have a medium sized flounder of which I can't get to eat anything other than fish to save my life. It eats silver slides and life fish. It won't even take on the brine shrimp. All the other fish eat the shrimp with no problem as well as the slides and live fish. My problem with the slides is that they don't really like them and tend to let the uneatend portions stay in the tank for a while (I feed them far less slides than I do anything else). So should I add brine shrimp and live fish in the tank at the same time so all my fish can be happy