Did anyone knows what can you do with that ?

If you return to the idol where poisoned the whisker you can give the item to the npc of this area and he will give a divine grass.

anybody tried to give the whiskers to the daughter of the dude that wants you to feed the carp? Cause the description says it give somebody joy knowing their mission is completed (mission to kill the carp from the daughter) and then it says the desire granted (the old dudes desire). I wanted to try it but the daughter died after i opened the door to the sanctuary

You cant give the whiskers to the Carp Feeder's daughter. She will just repeat her dialogue of warning you and asking to free the Carp Feeder until you use the whiskers to do so.

After you give the father the great white whisker the daughter will move to him after resetting the area (there are two daughters one near the Mibu Manor and the other is the one from the middle of the lake)

giving it to the guy who feeds the fish will give you a divine grass, but reloading the area sends his daughter by his side, and he will be dead. if you hold x or square to loot, you get 4 fish scales, so be sure not to miss them

Once you get the whisker, the Pot Noble merchant in the Fountainhead palace will die (?). By going to the Hirata Estate where the other Pot Noble is, there will be a Talking Colored carp, where he will sell the items of both Pot Noble merchants. Loot the pot from the Hirata Estate one and you'll find a Lapis Lazuli. The other Pot Noble from the Fountainhead Palace contains nothing.

Pity they all die. 1st daughter will be with father and will pass once you talk to her. The other daughter will be by the Palace Grounds idol inside the room with the red robed nobles knifing them until you talk to her so she may pass as well.

And my dumbass thought the daughter meant freeing the father of his duties by killing him. Well, that will teach you not to be so cryptic next time lady! But why does the dead carp show up in the sunken valley?