Yesterday my grandmother ate fresh tuna at a friend's party. She swears it was fresh and bought at a local fish-shop. The problem is, that we live in Gdańsk, by the south-eastern side of the Baltic sea and I have never heard of tuna in the Baltic. I told her that the fish couldn't have been local and therefore couldn't have been fresh but frozen and thawed. But the thought still bothers me, maybe tuna fish can reach the Baltic?
I did search a bit and found that tuna may be sometimes found in the Northern sea, so maybe it actually can travel so far east as to reach the Baltic? But the water in the Batlic is hardly saltwater (6-8‰), so would it be able to survive?