Yes, you can. I feed my little RES turtles fish all the time, and they love them! I just put a few live fish in their tank, and within a few minutes, they're gone.
Just go to your local pet store, and ask them for feeder fish, They usually sell for around 10-20 cents, so you can buy about 9-10 for about a dollar. Make sure you ask them for small feeder fish, though, if the turtles are small.
Yea that's good for them just go to a local pet store
(Ex-Petco) and ask for the feeder fish there small gold fish used for feeding Pets like your RES Turtle,
each one costs any ware from a nickel to 11 cents.
Good Luck!!!!!!