This has happened several times when I've cooked frozen salmon or other fish portions. Most recently I wrapped salmon in foil & cooked it on a grill -- covered most of the time. Then tonight I roasted a portion atop a bed of thinly sliced baby Yukon gold potatoes. Both times I had seasoned the salmon with good quality olive oil & s&p (added fresh herbs later). Both times it came out cooked through, more than I like, actually, with a frothy white scum on top. Quite unappetizing.
The salmon is "Atlantic farm-raised" from Chile (from Wegmans). Don't remember what the other fish was but it was a thick white fish, also from Wegmans. Any info on what might be causing this would be much appreciated -- TIA.