They are not fish eaters, but are herbivore's..... they have a diet of plants. If you want to feed him/her, then I suggest you start with things like strawberries, and melons. They will also eat some leafy vegetables, but not iceberg lettuce.
Washing your hands after handling any animal is good advise, but the turtles and tortoises don't carry salmonella unless they were fed a diet of raw meat. This only happened when people kept the small green turtles that they bought in Woolworth's or pet shops prior to 1973. In 1973, the interstate transportation of the green turtle was banned by the Federal Government, and the only place that I know of where you can purchase them today is in the very Southern states, where it is warm all year long. It is still illegal to transport them across state lines.