I'm not the biggest fish eater (to my shame, but the wife doesn't like it) so I won't pretend to know much about it. The best thing for me to do is direct you to the Marine Stewardship Council Web site which should tell you all you need to know about edible fish and has some fish recipe ideas too!
I have included a listing for fresh fish below as it was on seeing this shop, strolling around Newlyn harbour whilst on holiday in Cornwall, in the summer of 2009 that gave me the inspiration for this site!