Puffer fish or globe fish (family Tetraodontidae) are a group of tropical- and warm-temperate-dwelling species that are almost exclusively marine in their habits. A few freshwater species occur in tropical Africa and Asia. Most are typically found in shallow waters, often on coral reefs, in beds of sea grass, and in estuaries, swimming and feeding during daylight. A few species are oceanic. Their closest relatives are the similar-looking porcupine fishes (Didontidae) and the very much larger sun fishes (Molidae). Most puffer fish are recognized by their short, stout, almost bloated appearance, their small fins, and their large eyes. These fish swim by side-to-side sculling movements of the dorsal and anal fins, while the pectoral fins assist with balance and direction.
In addition to their characteristic body shape, puffer fishes can be distinguished from most other species by the fact that their bodies are virtually covered with large numbers of spines of unequal length. These are frequently more dense on the lower parts of the body. Normally these spines, which are modified scales, lie flat against the body. When the fish is threatened, however, it inflates its body by a sudden intake of a large volume of water or air, erecting its spines in the process. In this inflated stance, few larger species would be tempted to attack it and risk almost certain injury. Although puffer fish are unable to swim effectively in this position, the strategy is a deliberate antipredator action; instead of swimming, the fish drifts with the ocean current. In addition to this impressive defensive tactic, most puffer fish also contain a wide range of body toxins, particularly in the liver, gonads, skin, and intestine. They are widely thought of as the most poisonous of all marine animals; the various toxins attack the nervous system of species that eat them and may kill the animal unless it has the ability to detoxify the lethal products. Most puffer fish are brightly colored—a system often employed in the animal kingdom to warn potential attackers that their flesh is at best unpalatable and at worst lethal.
Puffer fish feed on a wide range of items. Some prefer to feed almost exclusively on plankton, but many species also prey heavily on large invertebrates such as molluscs, crustaceans, echinoderms, crabs, and worms using their sharp, beak-like teeth and powerful jaws to crush and sift through the defensive body armor that these other animals use in an attempt to protect themselves from predators. The teeth of most species of puffer fish are joined to form two sharp-edged plates in each jaw.
When resting, puffer fish generally seek out a concealed part of a coral reef or similar abode and hide away in a crevice. Some bottom-dwelling species nestle into the substrate; by altering the main colors of the skin, many are able to effectively camouflage themselves from the watchful eye of predators.
Although puffer fishes have an impressive arsenal of defensive tactics, some species may be threatened as a result of over-fishing for resale to meet the demands of the tourist industry. On many coral reefs, puffer fish are caught and dried in their inflated position for sale to tourists. Also, despite their lethal concoction of body toxins, the flesh of puffer fish is widely sought after as a culinary delight in some countries, especially in Japan, where the dish is known as fugu. Needless to say, the preparation of this meal is a delicate process if one is to avoid lethal poisoning. Some restaurants have been known to retain specially trained staff to prepare such dishes.