It would seem to me, with my poor logic skills, that a 'farm' bred animal, of any kind, would be exposed to any chemicals in its environment practically from birth to death. A 'wild' animal of the same type, would more likely spend its live in a more varied environment and usually a less polluted one, since it lives in a 'wild' area, one not occupied by man and his chemicals.
That would seem to explain the probability that 'farm' bred fish would have higher concentrations of whatever chemicals are in the water around them than 'wild' fish, especially if those fish normally have a large range of movement as do Salmon.
That second study confuses me even with its title. What is a "non-finned" fish?
I suspect that "fish" is being used in a generic way to encompass almost anything living in water? I suppose eels are included in that study, I just don't normally think of them as "fish." And that's probably due to my sheltered and somewhat land locked upbringing!
I guess I need to "get out more!" Or at least visit Google/Wikipedia more!