The Science Behind Pufferfish Puffing and Why They Do It

The pufferfish caught in a net in this fascinating YouTube clip gives a perfect demonstration of how they ‘puff’ their bodies up. One moment it looks like a regular fish, and the next it resembles a balloon floating on the surface of the sea. But how do these fish change their body shape so dramatically, and why do they do it? Read on to find out.

What Are Pufferfish?

There is no single species called a pufferfish. The term refers to a group of fish that can change their body shape into a sphere. They belong to the Tetraodontiformes order, and there are nearly 200 different species. Examples include the golden pufferfish, the striped toby, and the yellowfin pufferfish. You may also see them referred to as balloon fish, blowfish, globefish, or shellfish. They cannot move very fast as their fins are not large enough to propel them quickly through the water. This makes them vulnerable to attack by tiger sharks, octopuses, and sea snakes that prey on them. So, they need a clever form of defense to deter predators.

Inflation as a Defense Mechanism

When a pufferfish feels threatened, it inflates its body to around three or four times its normal size so that it looks like a balloon. They do this using a process called buccal pumping. They suck in water, which enters their highly elastic stomach. The stomach has collagen fibers arranged in parallel rows, allowing it to stretch and then return to its normal shape. If they are out of the water, they will suck in air instead. This, together with their specialized gill muscles and lack of ribs, allows them to achieve a spherical shape. You may have noticed that the pufferfish in this clip also has spines. When they are in a puffed-up state, the spines stick out from their skin, which makes them very hard for a predator to swallow.

The Downsides of Puffing Up

The process of puffing up is not something that the pufferfish wishes to do very often, as it has some disadvantages. When they are in this state, they use up five times more oxygen than in their deflated condition, and it depletes their energy. It also takes their metabolism between five and six hours to recover after inflating. As you can see in the clip, it is not easy for them to swim in this state. The pufferfish helplessly bobs around on the surface of the water, which explains why they quickly return to their normal state once the coast is clear.