I dont know if different species cross bread. The only fish I know of that cross bread are white and red springs. This is why the Vedder gets "marble springs."
Hey, ED, whoever told you that story was pulling your leg. Marbled chinook are not the result of red and white springs' 'interbreeding'.
The phenomenon of different coloration has to do with the absorption of carotenoid pigments.
I recently asked a fishery biologist about these fish and he told me that marbled springs are in reality your usual chinook salmon that have a recessive genetic feature, something about having
limited ability to absorb carotenoids, specifically
astaxanthin, which is found in shrimp, krill and many other salmon food sources. The result is a fish with some red flesh (usually closer to the backbone) and some white flesh (usually towards the edges).
Red-fleshed springs process this carotenoid pigment without any problem, and as a result, their flesh is nicely coloured throughout.
White-fleshed springs, OTOH, can't absorb astaxanthin
at all - resulting in the white flesh. White chinook are actually quite rare out of BC. AFAIK, only the Harrison run (transplanted to the Vedder) has a
predominantly white population.
Curiously, white-fleshed chinook are VERY much in demand in the US because they are rare - they constitute only about 1 percent of the total chinook population. It seems that some high end restaurants in the US are willing to pay premium prices for white-fleshed chinook, or as they call them "ivory kings".
This "marbling' of salmon flesh is mostly found in chinook salmon, but it has been observed in other species, particularly chum, albeit on a much lower scale. I have yet to undig a picture of a chum I caught in the Squamish a couple years ago. One fillet was almost white, the other was as red as that of a coho.
Anyway, to make a long story short, marbled-fleshed springs are marbled because of a genetic predisposition, not because they had one red and one white parent.
Cheers,
Milo
edited to add: red, white, or marbled - they are the same species!