I have a store near me called the aquarium warehouse that sells freshwater glass prawns that I'm trying to breed(not successfully yet) and i feed them to my turtles in a separate container. It's cool to watch them go on the hunt but it takes them a while cause the prawns are so damn quick, sometimes they jump out of the water about 10cms to try avoid their death.
I also have a lot of fish in with the turtles but they don't go after them, except for when I put food in the tank, then one of my turtles lets the fish knows who's boss, I have a comet that is really brave and takes food from in front of the turtle, he gets punished though and now has frayed tail. I don't think the turtle sees the comet as food yet (its too big) but is basically telling it to 'get away from my food!'
They also love blackworms and it gives them something to do for a few hours, getting them one by one out of the gravel.