I'm going to ask a biologist at the hatchery. I think it is a mark to indicate something. I saw Squaxin natives scanning fish heads with a wand (yes, scanning with a wand) and I saw those yellow dots on quite a few fish.
The dots are pretty obvious and I wouldn't confuse them with that naturally occurring yellow they get from something, (Nitrogen?) right around the gillplates (Onchorhyncus-Tsawytcha fungus?).

White Kings are well known. I'd agree thast they taste 'different'. The meat and flavor seem softer to me, from the couple I've eaten.
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Yup, taught 'em myself!