Our days of eating wild-caught fish are numbered with dwindling global fish supplies caused by overfishing. The fish that is available to us is increasingly contaminated with mercury and with other persistent organic pollutants (POPs) like Bisphenol A caused by the huge amount of plastic that has ended up in our oceans.
All fresh and smoked salmon available in Australia is farmed. Farmed salmon is an attractive alternative and may well bridge the gap we need to boost our omega-3 content. Here are some pros and cons of eating farmed salmon.
Omega 3 content
Farmed salmon traditionally contained higher levels of omega 3 than wild salmon, even though wild salmon has a more favourable omega 3 fatty acid profile. This is likely due to the overall fat content being up to three times as high in farmed salmon. In recent years however studies have found that the omega-3 levels in farmed salmon are dropping. This Australian study for example found that since 2002 omega-3 levels have dropped 30 – 50% in farmed salmon.
This is a result of the change in their diet – farmed salmon used to be fed on pellets made from small fish like anchovies and sardines, however, a reduction in the supply of these fish has led to other feeds being produced. These newer generation feeds can contain, soy, barley, algae, trimmings from seafood processing, insects and leftovers from processing almonds and pistachio nuts. There is also a genetically modified yeast that produces omega 3 that some salmon farms are using to bolster omega 3 levels.
This UK study found that farmed salmon that were fed on more vegetable oils were indeed lower in omega 3 than those fed on fish oil-rich pellets. It also found that the omega-3 concentrations in the fat of wild-caught salmon were higher. Even given this, the nutritional content of omega 3 per 100g was higher for farmed salmon due to the higher fat content of the fish.
Heavy metals and contaminants
Because fish can bio-accumulate toxins through the food chain it’s important to look at levels of mercury, dioxins, PCB’s and pesticides. Toxins levels correlate mostly with the feed given to the fish but also the environment they are grown in. This Norwegian study found that over a 13-year period from 1999 to 2011 contaminant levels of mercury, arsenic, dioxins, PCB’s and DDT had reduced, however, pesticide levels remained steady.
In this British study, they found that there were higher heavy metal concentrations in feed than there were in the farmed salmon. Mercury showed a slight degree of bio-magnification – meaning that it could be transferred from feed to salmon. Other heavy metals like lead and cadmium did not transfer across and became less available through the fish. The study found that overall mercury levels in farmed salmon were well below safety guidelines.
In this human study participants ate 380g of farmed salmon a week for 30 weeks and then tested for mercury and POP levels. No increases were found in these toxic compounds as a result of consuming farmed salmon.
The verdict?
Based on the research it would seem that farmed salmon is still a great candidate to fill our omega-3 requirements. Even with the decline in omega 3 levels brought about by the increase in the vegetable matter in their feed, farmed salmon is still one of the best sources of omega 3 by weight.
Because of the decline in our fish stocks, we’ll need to watch this space as new fish feeds are being trialled constantly and they will determine the quality of the end product. With the increase in man-made toxins and POPs studies will need to be conducted regularly to ensure that farmed salmon remains safe to eat.
