you have to go see the Zora prince after you recieve a letter from one of the Zora's in their domain...the Zora prince located somewhere else(can't remember) will give you the bait and when you get it, go back to the domain and try to catch the stinking fish.
I think if you go to Karkariko Village and go to the graveyard then crawl through the hole at the back of the graveyard he is starding at his mothers headstone, speak to hime there and he gives you and earring to use as a fishing hook to catch the fish you need.