How do you open the big fish mouth in the legend of Zelda ocarina of time?

if you mean in wind temple, i had issues too...here's how. go back to the room where makar was stolen, and go all the way to the top with your hookshot. go through the door. have makar fly up to the different pillars(with the command melody of course), and plant the seeds in the dirt spot. be careful at the top for there is a floormaster. when you are done planting the seed at the top, fly makar down to a different pillar. then have link hookshot all the way up, and defeat the floormaster. then have makar fly up. bring makar into the door, and have him and you step on the switches. then fly down when the fan is not going. step on the switch down below the fan. then go through the door. hope that helped! :-D if not, you're a qumquat.