In my experience you can keep Kinosternidae (musk and mud turtles) species with fish without much trouble. There's always a risk that the turtle will get nippy, but these species are far more interested in carrion (non-living food) or invertebrates than fish. Trionychidae (soft-shell turtles) are a different story.
Kinosternids are also a better fit for a fish tank because they don't need a terrestrial basking area. Most of these species will readily perform heliothermy (if they need to warm up) by floating on the surface and exposing their shell to the heat source. You'll need a relatively calm tank... probably one run on vertical sponge filters or undergravel filters rather than external filters and that doesn't have aggressive fish... fish can also kill a turtle after all.