Humans are not normally on a shark's diet. We are a foreign species to them, do not normally put out the "distress" signals (except for thrashing around on the surface) and, unless you are on a surf board, looking like a seal or a turtle in the surf, should be pretty safe. There are a number of noted exceptions to this, but for the most part this is true.
Tropical fish, up against a fence net, do not put out the "distress" vibrations that a "poked" fish will. Nor do they put any blood in the water. These are all things that attract and excite sharks.
