Hey Millertime,
I realize this is my first post and I am new to this site but I have done some extensivbe research on this topic in the past. In july 2005 after catching a spring in Neah Bay with the same yellow dot, I also became very curious as to what it actually was. I was told a "fishy" story by the fish counter/checker there on the docks. She said it was was put there by the state with a yellow permanent marker after it had been netted by Willapa Bay on the Washington Coast so the state could track what hatchery it eneded up at. There were three major things wrong with this story. First, these fish don't travel North, second, this was a wild fish, third and most important, have you ever tried to mark a live, wet fish with a marker? Wanting the real story, I took the fish down to Olympia, Washington where the head office is the state fisheries and that's where the states leading biologist works. I set up a meeting with him and showed him the fish. After getting a very good laugh at the story I was told, he told me what the yellow dot was. It's called a chromatafore, I believe that is the spelling. A chromatafore is also known as a birth mark. If you look closely at a spring, you can notice the gold tones in its skin color. We get birhtmarks from the meltonin in our skin which is what gives us are skin color and it is what moves to the surface to give us our tans. In springs, they just happen to be gold. I hope this helps.
that's a good one 'spring time'[
