What you see: Black spots on your salmon.
What it is: Likely dark pigments (“melanin spots”) the salmon produced in response to a virus or other disturbance.
Eat or toss: Melanin spots aren’t dangerous to eat, but cut around them if they bother you. And never eat salmon that smells off or is slimy.
Dark melanin spots on salmon are OK to eat
If you see black spots in your lox or salmon filet, you’re likely seeing evidence of a cell-level battle in the salmon’s past. The fish, detecting a virus or some other threat, sent in immune cells which produced a black antioxidant as the salmon healed.
The antioxidant is a type of melanin (and, yep, from the same family of pigments that darkens human skin and helps protect us from the sun’s harmful rays). Melanin also gives caviar and other foods their color.
When it comes to salmon, Norwegian food research institute Nofima reports that no harmful compounds have been detected in darks spots known as “melanized tissues.”
So, while they’re safe to eat, uninvited spots on your salmon still look bad. Seafood processors typically cut out darkened areas because they turn off consumers. But some mildly spotted cuts can still make it to your lox bagel or oven-baked filet.
And, unfortunately, you can’t cook yourself out of this one. Heat won’t make the discoloration go away. Though, I’ve found I noticed it less when salmon is cooked. And, of course, seasonings and sauces will make small melanin spots virtually impossible to detect.
A virus often triggers black spot production as salmon heals
Many cases of black-spotted salmon are attributed to an immune response to a specific fish virus. But by the time you buy your salmon filet, you’re probably just seeing evidence of the healing process in the melanin left behind. That could be pinprick-sized dots or dark areas a couple centimeters across.
In a 2015 article published by the Norwegian University of Life Sciences, these pesky spots were estimated to affect as many as 20 percent of fish at some farms and cost the Norwegian farmed salmon industry an estimated hundred million Euros per year.
The condition also affects farmed salmon in other parts of the world, and, while it’s been a particular problem in farmed fish, it also shows up in wild salmon. Researchers have found that a high-protein, low-fat diet can help reduce the formation of dark spots. And, as of January 2020, Nofima reported that large melanin spots were becoming less prevalent.
Spots can also contain blood or scar tissue
In some instances, scar tissue and blood can also cause or contribute to the discoloration. While unappetizing, these also would not render the food unsafe as long as it was properly cooked.
However, blood spots can reduce the salmon’s shelf life, causing it to lose nutrients and soften faster than it would have otherwise, Weizhi Wang reported in her 2016 master’s thesis at the Norwegian University of Life Sciences. In her research on pigmented spots on salmon, she also noted that it was unknown whether melanin deposits would affect the shelf life of salmon.
Are you definitely seeing melanin spots?
I shared the sashimi and lox images in this post with Turid Mørkøre, a senior scientist with Nofima. She said that while it was difficult to say for certain without lab analysis, they looked like melanin spots.
So, we’re sure that melanin spots are safe to eat, but what if you aren’t sure you’re seeing melanin spots?
First off, melanin spots are relatively common and therefore the most likely explanation. Though many affected cuts are culled, it’s relatively easy for salmon with small dots to make it to consumers. Brian Himelbloom, emeritus professor of seafood microbiology at the University of Alaska Fairbanks Seafood Marine Science Center, said he was not aware of any circumstances in which black dots on otherwise healthy salmon indicated a food safety risk.
Whether or not you see black spots, if your salmon has an off odor, is slimy or appears to be deteriorating, those are all signs that there could be increased microbiological activity and you shouldn’t eat the fish.
- Turid Mørkøre. Nofima, Senior scientist. Norwegian University of Life Sciences, Professor. Emails exchanged in Feburary 2020.
- Frequently Asked Questions: Dark Spots in salmon fillets. Nofima. Updated Jan. 2020.
- Melanin Deposition in Salmon Fillets. Nofima (as part of the FHF project, the Norwegian Seafood Research Fund.)
- Health Challenges: Dark spots. Biomar.
- The effect of dietary antioxidants on hyperpigmented fillet spots of Atlantic salmon (Salmo salar L.) Weizhi Wang. Master’s Thesis 2016. Department of Animal and Aquacultural Sciences.
- PRV ‘probably linked to black spots’ in salmon. Fish Farming Expert. 8/27/2018.
- Riddle of Dark Spots on Salmon Solved. Norwegian University of Life Sciences. Mette Risbråthe. Updated May 23, 2017.
- Nutritional effects on dark fillet spots of Atlantic salmon (Salmo salar L.). Poster. Turid Mørkøre, Yuqiong Meng*, Thomas Larsson, Kjell-Arne Rørvik, Katerina Kousoulaki, Gerd M. Berge, Bente Ruyter. Nofima, The Norwegian Institute of Food, Fisheries and Aquaculture, *Ocean University, Qingdao, People’s Republic of China.
Special thanks to reader ZE of Washington State for submitting images of his sashimi for this post!