I love seafood, and wild caught salmon and sardines are staples of my diet. I would never consider eating farmed fish, but are farmed shellfish/molluscs/crustaceans/etc. as bad to eat as farmed fish? In particular, I like shrimp and scallops, and can get them raw and frozen with no preservatives for reasonable prices, but they are farmed. Does it matter if either of those are wild caught, or will farmed suffice?
OK, I'll preface this with "yes, I saw it on Dr. Oz" but it sounded like something worth looking into:
Tiger shrimp tend to be farmed, and the way their raised is very unsanitary. I don't know what affect that has on their nutritiousness if any, but the description of their farmed environment sounded pretty gross.
I can't speak for all farmed shellfish, but 12 or 13 years ago I worked on an oyster Farm in Australia for a while and the key to growing oysters was good tidal flow, as this was where the oysters got their food (being filter feeders). They were "farmed" in open sea water as a result of this, unlike freshwater fish which can be farmed in really nasty conditions in ponds, tanks, etc.
You can also Farm sea fish in pretty nasty conditions, using onshore pens, but shellfish won't grow if the water isn't good. It's more economical to farm them in open water with free feed than in controlled conditions where you have to feed them.
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I try to avoid farmed shrimp. They can be pretty nasty. Mark did some great posts on this topic a while ago. The verdict is that farmed shellfish (oysters, clams, scallops, mussels) are fine, but crustaceans (like shrimp) are generally better wild:
An Introduction to Fish Farming | Mark's Daily Apple <- Discusses shrimp farming
Healthy Farmed Fish and Seafood | Mark's Daily Apple <--Discusses healthy farmed seafood choices
Grocery Store Seafood: What to Eat and What to Avoid | Mark's Daily Apple
This is kind of a neat site for seafood information: Seafood Selector
"Right is right, even if no one is doing it; wrong is wrong, even if everyone is doing it." - St. Augustine