Does iactare mean something else besides "to throw?" Because it's not often that somebody throws very many fish.
I have a vague recollection that it is a sport in the Silly Olympics (place of action: The Bundes Absurd Pool). On the other hand, I may be confusing it with the Fish Slapping Dance. Which may have it's origins in Rome, since apparently the ancients Romans did hit fish. Very enlightening, this course. Perhaps all will be unveiled once I get my owl.