Question: Why is a puffer fish big and fat?

Lauren Laing answered on 11 Mar 2016:

Puffer fish are believed to be the second-most poisonous vertebrates in the world!!! They are not always big and fat, this is a form of defence. The puffer fish moves by using pectoral, dorsal, anal, and caudal fins. This makes it really manoeuvrable, but very slow, and therefore an easy predation target. Its defence mechanism is to fill its extremely elastic stomach with water (or air when outside the water) until it is much larger and almost spherical in shape. All puffers have pointed spines, so a hungry predator may suddenly find itself facing an unpalatable, pointy ball rather than a slow, tasty fish.