Pufferfish

Pufferfish are typically small to medium in size, although a few species such as the Mbu pufferfish can reach lengths greater than 50 cm (20 in).

Tetraodontiformes, or pufferfish, are most significantly characterized by their four beak-like teeth – hence the name combining the Greek terms "tetra" for four and "odous" for tooth. Each of the top and bottom arches is fused together with a visible midsagittal demarcation, which are used to break apart and consume small crustaceans. The lack of ribs, a pelvis, and pelvic fins are also unique to pufferfish. The notably missing bone and fin features are due to the pufferfish's specialized defense mechanism, expanding by sucking in water through an oral cavity.

They are most diverse in the tropical zone, relatively uncommon in the temperate zone, and completely absent from cold waters.

Most pufferfish species live in marine or brackish waters, but several tropical genera, comprising about 35 species, spend their entire lifecycles in fresh water. These freshwater species are found in disjunct tropical regions of South America (Colomesus asellus and Colomesus tocantinensis), Africa (six Tetraodon species), and Southeast Asia (Auriglobus, Carinotetraodon, Dichotomyctere, Leiodon and Pao).

Many marine puffers have a pelagic, or open-ocean, life stage. Spawning occurs after males slowly push females to the water surface or join females already present. The eggs are spherical and buoyant. Hatching occurs after roughly four days. The fry are tiny, but under magnification have a shape usually reminiscent of a pufferfish. They have a functional mouth and eyes, and must eat within a few days. Brackish-water puffers may breed in bays in a manner similar to marine species, or may breed more similarly to the freshwater species, in cases where they have moved far enough upriver.