Nope, nature built them to eat raw fish. Just get good store bought fish. I have heard of certain types of fish are bad for them, don't remember which one. also heard salmon it to greasey and fouls your tank. I stick with tilapia and silver sides because a lot of people use them with good results.
fish are fish food.. and last i heard RTC's don't know how to cook. oily fish, like salmon and tuna can foul your water so feed that rarely if at all. all white meat fish, and small shell fish are what an RTC would normally eat in the wild. that would be a "normalish" diet.
Erm your thread title is hilarious.. no, they prefer fish grilled over an open fire with a side topping of coleslaw lol
Salt water and fresh water diseases generally don't cross over. That should be the least of your worries. I would gut the fish first. Thats were most of the parasites are.