I agree with Tom, that multi million year evolutionary split between the old and new world might be a bit too much to allow for recognition as cousins.
Jewels have been introduced to Cuatro Cienegas in Mexico and as far as I know, have not interbred with Herichthys minkleyi. In fact, it seems the introduction has had a negative impact on the ecosystem, and those people that care(such as the Desert Fishes Council), are trying to rid the area of the alien invaders.