fake fish

I read occasionally of fish that is sold as another species than what it really is. About the only fish we bring home that isn't in a can is cod. Some of what we get is nice, big flaked and tasty--sometimes even with that mild, buttery flavor we love in cod. Sometimes, it is tough, stringy and strongly fishy, what the mother-in-law refers too as mattress stuffing. Oftentimes, we get both from the same store and in the same packaging. My question: How can you tell generally what you are getting? And how, specifically can you tell if what is being sold as codfish is indeed codfish? Thanks.

There is, unfortunately, nothing new about this practice. When I was a kid, back when there were wolves in Wales and snakes still in Ireland, all "sea scallops" were exactly the same size.  Turns out they weren't scallops at all, but, rather, the flesh of skates that had been punched out to resemble scallops. 

I found it ironic that the FDA list included a sub for the more expensive Orange Roughy, which, itself, had been something of a trash fish with an off-putting name (dogfish, maybe?) until Aussie marketing types renamed it and built it into a highly desirable species.