The fatty acids DHA and EPA - docosahexaenoic acid and eicosapentaenoic acid - found in farm-raised salmon and rainbow trout have steadily declined by more than 50 percent over the past ten years, according to the consumer magazine Kuluttaja.
Kuluttaja cited research at Stirling University in the UK, which examined fatty acids in farm-raised salmon in Scotland. However, the fatty acid levels have dropped even more dramatically in Norwegian farmed salmon, according to the publication.
The reason behind the decline, the researchers say, is due to what the fish are fed. Previously farmed fish were commonly raised on a diet of fish meal-based feed but due to overfishing, farmed fish generally eat a vegetarian - soy or fava bean-based - diet.
Overfishing caused the market price of fish meal and fish oil to increase, the magazine writes.
Not all bad news
However, from an environmental perspective - less overfishing in open waters - the change is a positive one. When salmon eat a vegetarian diet, the magazine writes, they also eat fewer pollutants like PCBs and dioxins - resulting in less pollutants ending up on the dinner table.
The use of vegetarian feed by fish farmers has also helped to keep down market prices of their fish.
By far, the most popular fish in Finland is farmed Norwegian salmon and among domestic fish, rainbow trout is number one, according to Kuluttaja.
Eating farm-raised fish is not unhealthy, despite the decrease in omega-3 fatty acids, a researcher at the Natural Resources Institute Finland told the magazine.
Also, despite the decrease in fatty acid content, farmed fish remains the easiest way for people to get enough EPA and DHA in their diets.
According to Finnish nutritional guidelines, people should eat various types of fish two to three times every week.