Pufferfish

Pufferfish is an "edible" brewing ingredient caught by fishing.

However, actually eating a pufferfish gives the player Hunger III for 15 seconds, (total loss ), Nausea II for 15 seconds, and Poison IV for a minute, forcing the player down to for 48 seconds (30 seconds on peaceful). This makes eating pufferfish incredibly dangerous and non-beneficial. However, pufferfish can be used to tame ocelots without the chance of getting it poisoned.

Brewing a pufferfish into an awkward potion gives a potion of Water Breathing, which allows players to breathe underwater. One pufferfish is enough to produce enough potions for a maximum of 24 minutes of Water Breathing. Using a pufferfish as a brewing ingredient is the only way (aside from rare drops from witches) to get a potion of Water Breathing in Survival mode.

Trivia

 * The consumption of pufferfish inflicting the player with nausea and poison is actually based on reality, as real pufferfish contain the extremely dangerous toxin Tetrodotoxin within their organs, especially their liver. Muscle tissue and blood only contain trace amounts. In East Asia, pufferfish are considered a delicacy known as fugu, even though only small parts of the fish are actually edible.
 * If this dish is prepared incorrectly, it can be lethal through respiratory paralysis.