It's hard to tell with this photo, I guess it looks like sea cucumber spot.

The sea cucumber belongs to the family of roundfin fishes. It is a carnivorous fish with a short, thick body and is found in the icebergs on both sides of the Arctic and North Atlantic. Living in the seabed 200 meters deep, 0 degrees seawater, without any pollution, the natural environment to maintain the original ecological. The sea cucumber spot is purely natural and wild, and is a rare deep-sea cold-water fish species. The fish meat is snow-white in color, sweet and fat, smooth and tender in taste, the fish bone is soft and high in calcium, the fish skin is soft and hard, just like a sea cucumber. Sea cucumber spots are rich in unsaturated fatty acid "OMEGA-3" which can lower cholesterol, help prevent cancer, ulcerative colitis and arthritis, and is the main raw material of deep-sea fish oil. Now this product has become one of the most popular varieties of imported high-quality seafood.