Well, i have 2 red eared sliders and i had only put fish in there so that they can eat them. Turns out after a few weeks, if the turtles havent eaten them they all become "friends". But, if i put different fish in there they can tell the difference and try to eat those "new" fish.
If you are willing to take a chance and put fish in with your turtles, is a 50-50 chance. keep in mind that it doesnt matter what type of fish it is, the turtles just might snack on them.
Also, that little turtle, depending on what type, can grow from 6inches to even 2feet big. (my red eareds grow a max. of 11inches, and i have them with fish, etc. in a 55 galllon tank)
GooD LucK on what you decide!!!