Tetraodontidae

Puffer fish are amazing sea creatures that can puff up like a ball when they feel scared! But be very careful, because even though they look cute, they have a powerful poison inside their bodies that can make people very sick if eaten or touched. It's best to admire them from a distance.
The poison in a single puffer fish is strong enough to kill 30 adult humans, and there's no known antidote!
This one is poisonous, which means it hurts you if you touch it or eat it. It cannot chase you, so the rule is simple: look, do not touch.
Always ask a grown-up before you touch any animal or plant. If something bites or stings you, tell an adult right away.
Source: SeaWorld
Read more about the puffer fish at Wikipedia.