Puffer fish have a very unique defense mechanism. They are able to swallow water to inflate their bodies like balloons. Most fish will eat anything that will fit into their mouth, and avoid anything bigger than themselves. By puffing up like this, a puffer fish quickly jumps to a much bigger size, and becomes inedible to most fish.
A puffer fish spends most of its time deflated. In this state, it is much more streamlined and can swim unhindered in search of food. When it puffs up, it moves extremely slowly. I used to catch puffer fish by startling them into puffing up. This made them suddenly almost immobile. I could then easily pick the little ball up with my hands.
If I caught them in a net before they managed to puff up with water, they would fill up with air. This turned them into little living balloons. I would put them on the surface and they would float down the beach until they relaxed and deflated.
Puffer fish come in many colors, shapes, and sizes. Most can easily fit into the palm of your hand, but some grow as big as a person. Some species are decorated with beautiful colors as well.