someone may have mentioned this (you'll have to forgive me for not wanting to search through the 110 other pages) but i just found out, if a villager asks you to catch a fish and you offer them an extremely rare one, the game gives you an option to change your mind. (i assume this is also the case for bugs.)
i learned this because i forgot the barreleye was so rare because it wasn't in new leaf. but rowan was so happy, even though we're not close i'd feel so bad if i took it back...i spent the next half hour or so trying to find another one to no avail. it's really not a big deal, i have more than enough bells and i'd already donated the barreleye to the museum, but it does sting a little that i essentially lost 15k bells from my ignorance.