Which fish inflates its body to deter predators?

The fish that inflates its body to deter predators is the pufferfish. When threatened, many pufferfish rapidly take in water, expanding their bodies into a much larger, harder-to-swallow shape.

This defense works because predators may be unable to fit the enlarged fish into their mouths. In many species, the skin and internal organs also contain tetrodotoxin, an extremely potent poison. The toxin is not what causes the inflation, and not every pufferfish species is equally toxic.

Pufferfish are often confused with porcupinefish, which can also inflate and may display prominent spines. Both belong to the broader order Tetraodontiformes, but pufferfish typically lack the long external spines associated with porcupinefish.

After the danger passes, the pufferfish releases the swallowed water and returns to its normal shape. It is a remarkable example of a defensive behavior that combines physical enlargement with chemical protection.