Stay still
We’re not sure what the correct course of action is when you come within biting distance of a barracuda. Indeed, barracuda are delicious, but we’re just as appetizing to them as they are to us. This makes the OP’s experience even more frightening, especially when their surroundings went from happy to silent and grim in the blink of an eye.
While taking in the beautiful underwater scenery, groups of fish immediately split. The OP was confused until they found the source of distress: three barracuda. Thankfully, he was quick-thinking enough to stay put and let the barracudas swim away undisturbed.