I think its from the crabs that are in the Delta. Looks at Calico and Spotted Bay bass. They eat a lot of crabs and lobsters. Lots of yellow on those fish. I think the crustaceans have some sort of iodine type stuff in them that leaches into their skin. I could be wrong though. If you look at Etoufe (Sp?) sauce for crawfish it is yellow. That is all that fluid that is in the head of a crawfish used to make the sauce. Just a thought...