you guys are some of the most scared people of turtles I've ever seen. lol
I keep the snapper in my profile pic in with SA cichlids yes you do risk the fish getting scars and dying. however with that said soft shells don't have the jaw power to kill large fish like alligator and common snappers.but that said softys can still kill.
as far as taking fingers big common snappers and mid alligator snappers might be able to. large ones can do more but taking limbs is a bit of an over exaggeration. I have been bit by my snapper at 10 inches and a few big 18-19 inch softys and I still have all my fingers the worst that happens is a bit of pain a broken finger and some blood. we deal with it.
as far as your question
MrDuckBootz no I would not put that species of turtle in a 75 gallon. If you give everyone in the tank a place to get away from the turtle and other tank mates they should be fine. remember bigger is better I would give a turtle/fish t
ank 10 times the recommended tank size so if all the fish were 6 inches and the turtle was 3 inches i would recommend a 300 gallon tank the ratio should stay about the same for the rest of there lives.if everyone is feed and have there own space it should be fine but take it at your own risk.
also
NEVER FEED LIVE FISH!!!!
insects and pellets only
remember each animal is an individual and we can only look at the average for the species.