When the species are related closely enough and the habitat they occupy has considerable overlap, the sterile hydrid vigor theory you speak of may NOT hold true.

I believe there are naturally-spawning rainbow-cutthroat hybrids in some of the most famous SW tailwater trout fisheries.
_________________________
"Let every angler who loves to fish think what it would mean to him to find the fish were gone." (Zane Grey)

"If you don't kill them, they will spawn." (Carcassman)


The Keen Eye MD
Long Live the Kings!