Bonito is a name given to various species of medium-sized, predatory fish of the genus Sarda, in the mackerel family, including the common or Atlantic bonito (Sarda sarda) and the Pacific bonito. More generally, bonito can refer to any of various scombroid fishes related to but smaller than tuna.
In Japanese cuisine outside Japan, "bonito" usually refers to the skipjack tuna (Katsuwonus pelamis), which is known as katsuo in Japan. This fish is smoked and dried to make katsuobushi, an important ingredient in making dashi (Japanese fish stock), used extensively in Japanese cuisine.
Pacific and Atlantic bonito meat has a firm texture and a darkish color. The bonito has a moderate fat content. The meat of young or small bonito can be of lighter color, close to that of skipjack tuna, and is sometimes used as a cheaper substitute of skipjack, especially for canning purposes. Bonito may not be marketed as tuna in all countries, however. In Spain, tuna (Thunnus alalunga) is sometimes referred as Bonito del Norte.