Something fishy

Seems to be a lot of confusion about the whole, how much fish should/can I eat to be healthy, environmentally friendly, etc. In class yesterday, there was a brief argument concerning levels of mercury and other toxins in wild fish versus farmed fish. As well as I could figure, in the rather short time I've researched the issue, I've seen lots of accusations and some responses that seem valid to me. Perhaps a dialog mode would be most effective.

Ron: Farmed fish are better for the environment because with them we aren't depleting the wild stock.
Hermoine: Well, Ron, although we aren't eating the wild fish directly, the feed for the farmed fish comes from wild fish. So we end up with depleted stocks of those fish anyway. Some very progressive farms grow feed internally, but this is rare because it is expensive.
Ron: Hmm. Well, I've heard O-mega 3's are great for the heart, but I'm worried about mercury level in wild fish. In large quantities it can cause neurological disorders. Bloody 'ell I have enough trouble as it is. So maybe farmed fish can mitigate that risk...
Hermoine: Well, as I stated previously, the farmed fish are eating wild fish, so they'll have mercury in them too. But there is some debate over the levels of mercury that are dangerous. Some sources emphasize that "it has mercury, BEWARE." However, what really matters is whether there is enough in them to significantly adversely affect health. The FDA suggests limited intake for children and women of child-bearing age, but for others three is probably no reason to change eating habits due to concern over mercury. The EPA on the other hand has released an updated limit that is much much lower than the FDA's. According to the EPA's limit, some might consider reducing intake. In other words, there is no undisputed amount at the moment.
Ron: Okay, so I don't need to be too worried, right? Well, if it all comes down to cost, then I'm going for the farm raised fish. They're cheaper.
Hermoine: Well, Ron, do what you'd like, but let me mention two more caveats. First, other chemicals such as PCBs have been found in farm raised fish. Also wild fish caught closer to shore or in inland lakes have higher levels of potentially harmful chemicals. On top of that, some fisherman blame escaped farm fish for spreading disease among wild fish, which are not vaccinated, given antibiotics and so forth.
Ron: All this has gotten me rather afraid of fish. Am I killing myself and the environment?
Hermoine: I agree that there is a lot of spin out there, so it is hard to get a straight answer. Realize that many of these issues are similar to issues with other domestically produced meats. In my opinion, just limit fish to about 2 serving a week and perhaps less for high mercury fish like tuna, swordfish, and shark and you should be fine. Besides we have Madam Pomfrey if we do get ill.