Ok, from what I know from dealing with numerous reptiles and amphibians in the past is that snakes, and monitors are relly the only ones who can process mice easily. Turtles, lizards, salamanders, ect. cannot process the fats in a rodent so easily, and will soon become obeise upon extended feeding of this food item or if it comprises most of their diet. Most inverts are ok, as they high in essential vitamins, minerals, proteins and "good" fats. Larval insects (bloodworms, waxworms, maggots, ect.) are high in starches, sugars, and "bad" fats, and therefore, can lead to obeisity if they comprise the animal's whole diet. Crickets,Fruit flies, Earthworms, and various other annelids are ok, if supplimented with calcium to prevent (in the turtle's case) shell corrosion, (all reptiles or amphibians) or metabolic bone disease. They provide a stable non fattening diet for the animal. Also, stay away from feeder goldfish, as they are as bad as pinkies and waxworms put together. They are high in saturated fats, starches, sugars, and not to mention all the diseases that they carry. If you are going to feed the turtle anything at all in the way of fish, Minnows or feeder guppies are the two ways to go. Being vertebrates, their body automatically produces certain amounts of calcium to preserve the skeletal structures of the body, so they are slightly better than most other feeder animals, but there are downsides. Some feeders, being kept in the horrid conditions they're most often found in, sometimes carry diseases, most of which are non transmissable, but there are some that are. But the risk seems very low if the food is quarantined in a smal tank for at least 2 weeks to see if any visible prblems arise, but other than that, they're ok. Hope that this helped!
