The term "puffer fish" generally refers to pufferfish. Pufferfish has a cylindrical body with air sacs, and will inhale and expand when it encounters danger, and is generally 25-35 centimeters in length! Upper and lower jaws and teeth fused into 4 large dental plate, 1 dorsal fin, no ventral fin. No scales or small spines. Whole body oval, bluntly rounded anteriorly, tapering caudally. Snout short, rounded; mouth small, terminal, transverse. Upper and lower jaws each with 2 plate-like incisors, with distinct mesial slits.

Lips well-developed, with the ends of the lower lip curving upward on the outer side of the upper lip. The eyes are small, and the gill pores are small, a curved slit, located in front of the pectoral fins, and the body surface is densely covered with small spines. Dorsal fin very posterior to anal fin; no ventral fin; caudal fin flat-truncated at posterior end. The dorsum of the body is grayish-brown, the sides of the body are slightly yellowish-brown, and the ventral surface is white; the markings on the dorsum and sides of the body vary according to the species.

There are many species, most of which live in the sea, but can also be found in fresh water and at the confluence of sea and fresh water. They blow water and air through the water, causing sediment to fly up and then prey on creatures hiding in the sand. The teeth and jaws are tough and can crunch through extremely hard shells.

Expanded:

The notorious method used by black saddle pufferfish to avoid predators is to inflate their bodies with water, much like a person puffs out their cheeks to hold their breath. But unlike humans, who hold their faces blue -- and contrary to scientists' expectations -- the black saddle dolphin doesn't pause for breath, researchers report in a recent report published online in Biology Letters.

The scientists placed the fish in a clear plastic box where they could monitor its breathing. They poked the pufferfish with a tube that sucks up water, simulating a predator attack. As expected, the pufferfish responded by expanding as well as quickly sucking water into its enlarged stomach. And, contrary to previous beliefs, the respirometer showed that the pufferfish would continue to breathe in the process.

Scientists had suspected that the pufferfish might breathe through their skin rather than through their gills during the expansion process, but that suspicion also appears to have been wrong: Instead, the data and observations show that the pufferfish continue to breathe through their gills as usual. In fact, a comparison of respiration rates showed that the pufferfish's respiration increased nearly fivefold during the expansion.

Even if they didn't stop breathing, this defense strategy was extremely energy intensive for the pufferfish; after testing, it took most of them several hours to return to their resting respiration rate.

Baidu Encyclopedia - Pufferfish

People's Daily Online - Pufferfish Swell Without Forgetting to Breathe