Like many genera of turtle, Graptemys are omnivorous. This term means they eat both plant and animal matter.
Something to note about these aquatic turtles is that they only feed in water. They have greater mobility in the water and overall adapted to underwater environments to the extent that hunting food is far easier underwater than it is on land.
The type of food you give them will vary depending on which gender of map turtle you have. This is because the females are much larger than the males, and so their superior jaws can consume larger prey. The females can consume prey as large as clams and snails, whereas males have to be fed things like tiny crustaceans and aquatic insects.
Fish can be hard for them to catch, but they will sometime eat pieces off of dead fish. At pet stores, you can usually find items like frozen shrimp or meal worms, which can be thawed and then given to your map turtle. Do not feed your map turtles live meal worms. Live meal worms rich in nutrients but there is a small risk that the worms might harm your turtle.
A tip is to buy your frozen shrimp in the grocery store rather than the pet store. The shrimps are a lot cheaper in the grocery store and as long as you get brine free (unsalted) shrimps they will be suitable to use as food for your map turtles. I do this for my fish, turtles and other animals.
For plant matter, they enjoy dark leafy greens. Place the greens on their basking areas above the water, as well as have them floating in the water itself. If you have an outdoor enclosure, you can plant some aquatic plants and let them grow naturally. Research what kind of aquatic plants grow around the native area of your specific species of map turtle. There are other benefits to having aquatic plants in your map turtle’s outdoor enclosure, which will be covered later.
Typically, hatchling & young map turtles that are still growing will have a more carnivorous diet than their adult counterparts. This is because young turtles are still growing, and need the extra protein in their diet.