I made the stupid decision to bring my first ever legendary fish (crimsonfish) to the fair, and put it in the grange display. And, yeah, for the first time ever I forgot to reclaim my items... Didn't realise until the next ingame day. And I have no way of catching it again in the same save, right? :'(
Correct, Except for "The Legend" none of the other 4 fish will be able to caught again if you "loose" or misplace them, sorry :/
It may be possible via save editing to set it back as if you haven't caught it. The vast majority of single shot events can be reset in this fashion, but you'd need to dig around in the save and have the potential to bork your game.