This situation recently arose and I'm curious about what our members would do. SH
? If I unknowingly bought it I would keep it, then sell it or give it to an expert breeder.
/www.calacademy.org/ ) and make sure they put my name and picture on the exhibit once it goes up 
That's exactly what I would doKeep/buy it and make sure it ended up with a breeder. As others have said, its chances in the lfs is likely to be less than if I pulled out all stops for it.
Whether I notified the authorities would depend on why the species in question is endangered.

. The are on the IUCN red list , they are endangered from over harvesting. For some reason though you can easily get these fish from Petco for $12. I have 3 and i'm hoping to try to breed them as soon are i find a female, which so far has been very difficult