Most of tuna aquaculture production still relies on the capture of juveniles caught in the wild, as this volume explains. Ranching, fattening, and farming all refer to this type of production, and these terms are frequently used interchangeably. Ranching and fattening, on the other hand, are distinct from farming in the real sense. The short-term activity of holding subadult or adult tuna mainly for the purpose of improving their condition and fat content, thereby increasing their market value, is more accurately described by the former two terms. However, substantial increases in biomass are frequently achieved as well. Australia, Mexico, and many producers in the Mediterranean use this method. The period of ranching or fattening varies from region to region, but typically only takes a few months. In the last ten years, the use of such fattening methods has increased dramatically to the point where, before being sold, a significant portion of all blue fin tuna captured in many areas of the globe are stocked into cages to increase their size and fat ratio. This practice may be considered a “value-added” process despite the inherent issues of the operation—they are fed sardines and similar forage fish that are ecologically critical—because the primary value of the tuna stored in the cages rises significantly in what can be considered a more powerful and ecologically resourceful manner than would exist in nature.
