I have an aquatic turtle like yours – mine is a red eared slider. though, and not a map turtle. Be prepared for your little guys to get BIG! My slider is about 10 years old and has a carapace about 8″ long; she lives in a 75 gallon tank, which is really a bit small for her. She’ll eat anything in sight – fish, shrimp, and a steady diet of fruits and veggies that I feed her. Your map turtles will eventually start trying to eat the fish in your tank, so separate them out if you desire to keep the fish at all.
They make great pets, though. I love my slider and have spent many happy hours watching her swim and chase fish in her tank. She’s tame enough to take mealworms from my hand without biting me, and she loves the occasional scratch on her chin!