
It's Salmon, the reason I prefer the Lamb is that sheep tend to be out at pasture so basically free range, and salmon is likely to be farmed, with all that goes with that, though they say they use wild (and chickens and ducks intensively reared).
None of my friends have had issues, but would they know?
If I had any worries over the the mercury though I'd use one of the other sensitive range, Lamb duck or chicken with potatoe.