Farmed salmon, aka [salmon], are kept under artificial lighting to mimic summer year-round, bypassing the "mating season" in which salmon naturally lose weight (not useful in [salmon] farming)
Accelerated growth induces growth abnormality and deformations, stress, and become susceptible to parasites such as sea lice (which thrive in the crowded conditions they are kept in)
To get rid of sea lice, [salmon] are sometimes splashed in boiling water to detach the parasites. Accidental boilings are "not uncommon".
[Salmon] don't/can't get fed krill (why?), and so they are naturally grey and have to be fed food dye pellets for their flesh to become pink as consumers expect them to be (The SalmoFan™, Pantone for salmon)
To prepare [salmon] for the market, they get starved for up to a week to clear their digestive tracts of excrement. Cannibalism can result.