Live supermarket seafood
So, there is a little Asian market about two blocks away from me that sells live fish from the tanks (along with whole dead fish, filets, steaks, frozen seafood, etc too). The price is decent (some stuff is actually cheaper since they don't have to do the cleaning, butchering, etc). And, unlike a couple of other Asian markets I've been to, crystal clear water in the tanks. My concern is their feed. I don't know what the supermarket feeds them, and there is a huge language barrier. So, unless I either learn Chinese or get myself a Chinese girlfriend...my neighbor is really cute.....anyways...I have no way to know what they're fed.
The place is always busy, so none of the live seafood stays in the tanks very long. Some of it, like the crab, they get live from the wild (according to their poorly written English signs) and the rest I assume they get live from fisheries. How bad of a feed (GMO-soy and what not) do you think they're being given? With the large turnover, should I assume it won't be any more unhealthy than the already dead alternative (farmed catfish filet vs whole, live catfish; dead wild crab vs live, formerly wild crab)?
My own experience here is with a local asian fish store that also has many other asian products. At first I though it was wonderful although there's no english translation on anything. Later I asked the employees for translation, which was a very slow process. What I learned was that there were bad chemicals added to or fed to almost everything. I don't shop there anymore unless my hubby wants real sticky-rice.
Sadly, you need to expect the worse. It's likely it is all been fed the cheapest feed possible, which is generally soy based.
Go for leaner fishes in that case. The fat is where the good and bad lie. So when you have to choose a conventionally raised food, generally lean is always better. (Same goes for pork, chicken, beef etc.)