How to combat Asian carp? Get an alligator gar

's a toothy giant that can grow longer than a horse and heavier than a refrigerator, a fearsome-looking prehistoric fish that plied U.S. waters from the Gulf of Mexico to Illinois until it disappeared from many states half a century ago. Persecuted by anglers and deprived of places to spawn, the alligator gar — with a head that resembles an alligator and two rows of needle-like teeth — survived mainly in Southern states in the tributaries of the Mississippi River and Gulf of Mexico after being declared extinct in several states farther north. To many, it was a freak, a "trash fish" that threatened sport fish, something to be exterminated.  But the once-reviled predator is now being seen as a valuable fish in its own right, and as a potential weapon against a more threatening intruder: the invasive Asian carp, which have swum almost unchecked toward the Great Lakes, with little more than an electric barrier to keep them at bay.  Efforts are underway to reintroduce the alligator gar to the northern part of its former range.