WWF use their logo as a seal of approval where quality standards...

WWF use their logo as a seal of approval where quality standards have to be met. Tassal has certification with the 'gold standard' in aquaculture (ASC).

Fish swimming with their mouth open as an isolated fact is no indication of an issue as that is part of how their respiratory system operated. Mouth opens, water flows through gills. However, the evidence to your point you didn't raise is that the oxygen levels have been depleted/volatile, which would cause obvious issues.

I think the worst case scenario in all of this is that Tassal have overstocked some locations. They should decrease the density and burden on some waterways and use more open sea pens. However, such a move would be at the expense of the bottom line and profits, at least in the short term.

IMO...