I would love if the game handled all items that have knowledge levels the same way it handles seeds: e.g. a "congratulations! You've discovered [tree]!" notification akin to the one you get for new seeds. I would like to know when it's time to go back to grandpa to get more saplings!* Same with the fish: having a "hooray! Your knowledge of this fish has increased!" notification would make fishing soooooo much more motivating for me. As it is, there's no real feedback of progress, which is a shame since there is a whole process mechanic there.
*As something of a sidenote, it took me until my third game to figure out that I could have been buying saplings at the plant nursery all along. So maybe that notification text could have an addition such as "you can now buy the saplings at the nursery" or something like that.