The yellowtail is a shusseuo, or a “promoting fish”, which means that it has different names according to its size, and age.
These names are also given to make clear distinctions of its taste, and to easily recognize what kinds of food preparations are most optimal for it.
In 1970, yellowtail started to be farmed in the inland seas of Seto and continues to be done so, and has improved in quality throughout the years.
To make things confusing, these yellowtails were given the name hamachi, although the name was already used in the Osaka dialect to name the same, but younger yellowtail.
Nevertheless, the name was taken to name the new farm raised yellowtails. It is often confused that hamachi is a young and it still may be called so in the Osaka region, however, the Edomae sushi is a Tokyo cuisine, and they refer to hamachi as the farmed version of yellowtail.
Since the yellowtails are farmed inside fish nets immersed in the sea, they do not get much exercise as the natural buri, which swim thousands of miles in their average lifetime. As a result, they become very fat, the muscles become very soft, and the flesh has a lighter color.
When natural and farmed raised yellowtail are compared, there is a noticeable difference besides the color and texture of the flesh, and that is the quality of the fish oil. The natural yellowtail is also a very oily fish, but the oil is lighter, and sweeter than the farmed raised version. For this reason a citrus flavored soy sauce matches with the farm raised very well.