Although many might say it's a bad idea, I've had a lot of luck with keeping soft shell turtles together with similar sized or larger fish. The turtles ate feeders and small fish eagerly but left all tankmates their size or larger alone (even slow moving fish like catfish providing they were big). Went on vacation for almost a week, threw in a couple dozen feeders, came back and everyone was hungry but no injuries/fatalities. Would probably be better off with a male as they don't get as large as the females.