Eating sushi can be done witha reasonably clear conscience as long as you are getting the right stuff. There are lots of groups which give lists of sustainable food choices. It has been really hard for me to give up maguro/bluefin, but I have. In place, I eat a lot more salmon sushi, whish as someone earlier said, is sustainable. It can be eaten in a responsible way.
http://eng.msc.org/assets/docs/MSC_annual_report_05_06.pdf