Here are two cuts of Hamachi, or Yellowtail.
The top cut is from the top/back loin of the yellowtail is much more lean than the lower cut, of which is from the stomach. Rule of thumb is that more fat means more flavour; thus more desirable and sometimes more expensive.
However, the current stomach cut that is pictured still has the stomach lining and the rib bones still in, so the meat that is consumed is not really exposed in it. Just too note, the stomach meat is much shinier and more oily.
Hamachi has a rather sweet and (from the stomach) somewhat buttery taste too it. Some of my customers have described it's texture as a 'melt-in-your-mouth' sensation.