I really like sushi, but I've noticed that at one of the places I buy it from (a small but reasonably well known chain), a lot of the salmon seems to have red lines in it lately. I got a refund the first time I found a couple of small ones, but the second time the manager told me that it was probably just seasoning or something else that had touched the salmon. They seem to bleed if squashed with a chopstick but he was having none of it!

This is a picture of a set that I didn't buy, but seemed like a pretty good example. I've tried Googling but can't work out what it is. Does anyone have any ideas? I haven't eaten salmon from there since as the thought of these things grosses me out...

http://tinypic.com/m/jie5wz/4

Could it be the blood line?

That would make sense - I kept searching for 'fish veins' but didn't seem to get much! The first time I went back (I was concerned they may be worms or something after seeing a food show about cod) the person said they might not have prepared the salmon properly and left too much on. When I mentioned that to the manager the second time he told me that the fish blood is all drained and that it definitely wasn't blood. I've been eating sushi regularly for several years and I've never had a problem with salmon anywhere else, so I wonder if it's intentional to save a bit of money - I've looked in several packets when deciding what to get and they're probably visible in about half of them... funnily enough they only started appearing when a new sushi restaurant opened nearby!

As far as I'm aware, the blood line isn't harmful, it's removed to make the fish appear more aesthetically pleasing, although I imagine it might taste a little bitter.

Yeah I think you're right after I've done some more Googling - appreciate you taking the time to respond as it's put my mind at rest! The manager's attitude sucked though so whilst I'll still eat there occasionally, I won't feel like a traitor when eating elsewhere