So far, mine has not. I've only had this for a few months though and I hang them in a mesh bag to dry. The fish are sealed and water doesn't get in them, which I like. However, the rod itself, water drains out of it when you take it out of the tub. So as for that, time will tell.
Water gets into fishing pole, but has 2 open areas on the ends where it drains out easily and drys well. Little toys do not get water in them. We've had this toy for about 6 months, gets weekly use at least, and I have not noticed any mold.