Sushi [moved from Food Media & News board]
Only way to find out is to ask the sushi chef. If you go to a good sushi spot, they can tell you where all the fish came from. If you go to the typical run of the mill where they get their fish from some generic vendor, who knows where any of the fish comes from? Salmon from different places taste different. Different cuts from the same fish also taste different. Just like different cuts of beef taste different due to texture and fat content.