Where to get an offering fish for Jabu-Jabu in Ocarina of Time

You need to make an offering to Jabu-Jabu in Zelda: Ocarina of Time remake before you can rescue Princess Ruto. However, the game is rather vague about what constitutes an offering, though Jabu-Jabu's more devoted followers do give you a hint. Assuming you look in the right place, that is.