With these conditions being the way they are these farmers, similar to the feed lot owners on land, choose to heavily medicate their fish with antibiotics and hormones to keep them healthy in such an unhealthy environment. Over 80% of all antibiotic use in the U.S. goes to feeding livestock, and it's estimated that farmed salmon are fed more antibiotics per pound that any other livestock in North America. More here " This leads to questions as to why this is seen as appropriate in this industry of fish farming when is is some contested in other farming operations.
The major problem found in this study that there is not very much testing done to differentiate between fish farmed in a hormone free environment and those that are not. “Europe inspects 20 to 50 percent of imported seafood. Japan inspects about 20 percent; Canada, 2 to 18 percent; and the U.S., just 2 percent. More here.
If you are a concerned consumer and want to be knowledgeable about the conditions of the fish that your are consuming there is almost no way to isolate those raised with undesirable drugs from that though that were not. It would seem in the best interest of all consumers to at least have this information available to us. It is hard to say though that by simply switching to wild caught fish you can avoid all of the problems. This is a very good resource for finding explanations of the benefits to both farm-raised and wild-caught fish and it includes some useful information here.