Many environmentalists have an anti-meat, anti-production bias. If these researchers are anything like the activists posing as scientists who constantly attach the grain, cattle, and pork industries, I wouldn't worry about the integrity of farmed fish available for purchase in your area.
In my area of agriculture (Seed Corn and Seed Soybean), every few years some grant-chasing activist with a job at some University or Institute will come out with a report saying that "Hybrid X" is the worst thing under the Sun, and will lead us all into a 1,000 year reign of darkness, blah blah blah. Then two years later, another scientist will publish an article saying something along the lines of: "The article about the dangers of 'Hybrid X' may have been greatly exaggerated. Our testing could not replicate our colleagues findings at all".
This article was designed to scare you away from a certain food choice. You have to ask yourself, why are people trying to scare you away from this food type, and who benefits because of it?